Borg Warner Delco Remy 28MT Reference guide

Diagnostic
Procedures
Manual
For Starters
and Alternators

Table of Contents
I ) Introduction and Description
1–1. Introduction 1
1–7. Description 1
1–12. Electrical Fundamentals 2
II ) Diagnosis Charts
2–1. Overcharge Symptoms 8
2–2. Undercharge Symptoms 9
2–3. Milled Pinion Symptoms 10
III ) Testing
3–1. Testing Freedom Batteries 11
3–4. Testing Conventional Batteries 11
3–5. Test Procedure 12
3–7. Battery Cable Test with Single-Battery Location 12
3–10. Battery Cable Test with Dual-Battery Locations 14
3–13. Starter Solenoid Circuit Test 14
3–18. Magnetic Switch Circuit Test 16
3–21. Starter Replacement Determination 17
3–26. Alternator Wiring Test 18
3–29. Alternator Replacement Determination 19
3–33. Completion of All Tests 20
IV ) Summary
V ) Appendix
5–1. Smart IMS or SIMS Diagnostic Steps 22
5-2. Overcrank Protection (OCP) Circuit Check 23
5-3. Multi-Battery Charging with Series and Parallel Chargers 23
5-4. Group Charging on Current-Limiting or Series Chargers 24
5-5. Group Charging on Voltage-Limiting or Parallel Chargers 24
5-6. Heavy Duty Diagnostics Procedures Data 25
Section Page

delcoremy.com Page 1
1-1. INTRODUCTION
1-2. PURPOSE. This manual provides diagnostic procedures that
can be used for troubleshooting a heavy duty electrical system,
including the starting and charging systems. Some procedures
also may be used for preventative maintenance checks. These
procedures are applicable to systems using heavy duty starters
such as: Delco Remy 28MT™, 29MTTM, 31MT™, 35MTTM, 37MTTM,
38MTTM, 39MTTM, 41MTTM, 42MTTM, 50MTTM or a similar starter with
adequate battery power for the engine/starter application used.
1-3. DEFINITION OF DIAGNOSIS. Diagnosis is the three-part
process that begins when a problem is perceived and ends when
the equipment is confirmed as serviceable. Three questions must
be answered to assure completion:
1. What are the symptoms? This is what has been observed
(seen, heard, felt or smelled), indicating a problem.
2. What caused the symptoms? Diagnostic procedures are used
to identify the root cause of the problem.
3. How do we fix it? Usually this involves the adjustment, repair
or replacement of some part or parts.
1-4. This manual defines the procedures to determine the cause of
the symptoms. Actual adjustment, repair and replacement procedures
are provided in unit-specific service bulletins and manuals.
1-5. For educational purposes, study of this entire manual is
recommended. For diagnostic purposes, the flow charts in Section
II will reference appropriate procedures for specific symptoms.
1-6. EQUIPMENT REQUIRED. To perform the tests specified in
this manual, the following equipment is required:
1. A variable carbon pile load tester with more than 500 amps
capacity with ammeter (and voltmeter).
2. A separate DC voltmeter, digital preferred, capable of reading
0.01 volt increments.
3. An inductive (clamp-on) ammeter for safe and accurate
current measurements.
4. A hand held or bench top type tester.
1-7. DESCRIPTION
1-8. SYSTEM. The heavy duty electrical system is comprised
of the starting and charging systems. These systems are, in
turn, comprised of batteries, the starter, the alternator, and the
interconnecting wiring and electrical and mechanical switches.
For maximum operating eciency, all parts of the system must be
functioning properly.
SECTION 1
Introduction and Description
FIGURE 1-1. Heavy Duty Electrical System
1. Battery
2. Starter
3. Alternator
4. Magnetic Switch
5. Push Button Switch
6. Key Switch

Page 2
1-9. BATTERIES. Batteries are perishable devices that wear out
at some point in time. With use, they deteriorate and eventually
become incapable of performing their important job. In addition,
new batteries may become discharged for various reasons.
Neither worn out nor discharged batteries can supply the power
necessary for cranking. Thus, the battery check becomes the
starting point for diagnosing electrical system problems.
1-10. SUBCIRCUITS. Because of vibration, corrosion, temperature
changes or damage, the performance of wiring, connections and
secondary components as well as the function of the starter and
alternator can deteriorate. This, in turn, can cause malfunctions
within the starting and charging systems. For the purpose of
testing, wiring and components are divided into four circuits that
must be tested. These are:
1. Cranking Circuit. This consists of the large cables that carry
the high starter current. Excessive loss here causes slow cranking
speeds, especially in cold weather. Inability to start from slow
cranking can lead to starter damage if the starter is cranked over
30 seconds. Deeply discharged or worn-out batteries also can
cause the same problem.
2. Solenoid Circuit. This consists of the wiring from the battery,
through a push button or magnetic switch, to the S terminal of
the starter solenoid, and back to the battery. Excessive loss here
can cause the solenoid to shift in and out (chatter), resulting in a
no-start condition. This can cause a damaged contact disc and
terminals of the starter solenoid. Deeply discharged batteries also
can cause this problem.
3. Magnetic Switch Circuit or IMS (when the magnetic switch is
used). This consists of the wiring from the battery, through a key
switch and/or start button, to the coil of the magnetic switch, and
back to the battery. Excessive loss here can cause a “no start”
complaint.
4. Charging Circuit. This consists of the wiring between the
alternator and the battery and back to the alternator. Excessive
loss here can cause the batteries to not charge properly. As noted
above, discharged batteries will cause other problems.
1-11. SEQUENCE OF PROCEDURES. It is important that these
procedures be followed in the exact sequence specified. Batteries,
wiring and connections should be checked and corrected to
the specifications given. If cranking problems still occur, then
connecting cables should be checked before replacing the starter
with a known good unit. Similarly, in the charging circuit, the
batteries, wiring and connections should be thoroughly checked
and corrected to the specifications given. Only then should the
alternator be checked and replaced if necessary.
1-12. ELECTRICAL FUNDAMENTALS
1-13. TERMS AND DEFINITIONS. The following are electrical terms
and definitions used in this manual:
1. Voltage. Voltage is the electrical pressure or force that causes
current or electrons to flow through a conductor. The voltage
also can be described as the dierence in electrical pressure
between two points in a circuit. This electrical force or pressure is
measured in volts.
2. Current. Electrical current is the flow or movement of electrons
in a conductor. This movement can be compared to the flow of
water through a pipe. Without pressure (voltage), the current
will not flow. Electrical flow is measured in amperes, most often
abbreviated as amps.
3. Resistance. Resistance is the opposition to current flow. For
a given electrical pressure (voltage), resistance decreases current
flow. This can be detected by voltage loss or drops in the electrical
circuit. Electrical resistance is measured in ohms.
4. Magnetic Field. When electrical current flows through a
conductor, a magnetic field is produced around the conductor.
By measuring the strength of this magnetic field, it is possible
to determine the amount of the current flow or amperage. This
principle is the basis for the function of the clamp-on or induction
type ammeter.
1-14. MEASURING VOLTAGE WITH THE VOLTMETER. The
voltmeter is used to measure electrical pressure or voltage. The
unit of measure is the volt. Voltmeters are always connected
across (in parallel with) a part of the electrical circuit (See Figures
1-6 and 1-7). The voltmeter measures the dierence in electrical
potential or pressure between the points where the voltmeter is
attached.
1-15. VOLTMETER SELECTION. Voltmeters for the purposes
described in this manual are DC instruments with a range as
follows:
1. Low scale: 0-3 volts
2. 12-volt vehicles: 0-16volts
3. 24-volt vehicles: 0-32volts
MAGNETIC FIELD
CURRENT DP-1005

delcoremy.com Page 3
NOTE
The use of digital voltmeters is highly recommended for the
following reasons:
• Digital voltmeters are generally more accurate than analog
(needle movement) instruments.
• Digital readings need no interpretation; everyone sees the
same number.
• Digital instruments are generally auto ranging; they
automatically select the proper range for the value of the
reading.
• Reversing polarity with a digital instrument will simply result
in a negative reading (minus sign) whereas with an analog
voltmeter, reversing polarity could damage the meter.
• If analog meters are not read directly facing the meter,
inaccuracies may result.
1-16. VOLTMETER USE. Figures 1-6 through 1-8 illustrate the
proper use of the voltmeter and the types of readings that can be
expected.
1. Figure 1-1 shows the voltmeter being used with no current flow
or with the starter not operating.
FIGURE 1-1. Voltmeter Readings with
No Current Flow
FIGURE 1-2. Voltmeter Readings with
Current Flow
NOTE
When the voltmeter is connected parallel to a cable (meter
leads and cable ends start and end at the same point), the meter
will measure the voltage potential at both ends of the cable.
Without current flowing, the values always will be the same and
the voltmeter will read zero.
2. Figure 1-2 shows the voltmeter being used with current flow
(starter pulling 500 amps).
NOTE
The V1 reading (See Figure 1-2) means that with 500 amps
flowing through the positive cable, there is a 1.0 volt drop in
that cable. There must be current flow in order to produce a
voltage drop. The V2 reading (See Figure 1-2) of 0.3 volt means
that with 500 amps flowing through the negative cable, there is
a 0.3 volt drop in the negative cable.
3. Figure 1-3 illustrates the digital voltmeter reading in a DC
system with both correct and incorrect polarity. Whenever the
minus sign is displayed, the meter leads must be reversed to
obtain the correct polarity.
0 V DP-1006
0 V
O V
V4
12.5V
0 V
V3
0 V
12.5 V
12.5V
V2
12.5 V
V1
0 V
0 V
12.5 V
12.5 V
DP-1007
0.3 V
0.3 V
V2
8.5 V
V1
1.0 V
7.5 V
8.5 V
V2
7.2 V
0.3 V
V1
0 V
8.5 V
7.5 V

Page 4
DIGITAL VOLTMETER
CONNECTED CORRECTLY
IN RELATIONSHIP TO
POLARITY
DIGITAL VOLTMETER
CONNECTED INCORRECTLY
IN RELATIONSHIP TO
POLARITY (VALUE CORRECT
BUT MINUS SIGN WILL SHOW
TO ALERT OPERATOR THAT
LEADS ARE REVERSED)
DP-1008
12.5
V1
-12.5
V1
FIGURE 1-3. Correct and Incorrect
Polarity Readings
1-17. MEASURING CURRENT FLOW WITH THE AMMETER. The
ammeter is used to measure current flow. The unit of measure
is the ampere or amp. Unless the induction pickup (clamp-on)
ammeter is used, the circuit must be opened and the ammeter
connected in series in order to take measurements.
1-18. AMMETER SELECTION. With but a few exceptions (See
Figure 1-10), it is desirable to make ammeter readings without
opening up the circuit and thus disturbing a circuit defect and
preventing it from being discovered. Therefore, the use of a
clamp-on induction-type ammeter is recommended for most of
the measurements described in this manual. This type is easy to
use, cannot be damaged by misconnection, and will not damage
the vehicle wiring. A clamp-on ammeter operates by measuring
the magnetic flux produced by current flow through a conductor
and translating that into amperes, which are displayed on the
meter readout.
1-19. AMMETER USE. Figures 1-4 through 1-6 illustrate the use of
various types of ammeters.
1. Figure 1-4 illustrates the use of an in-line digital ammeter.
Note that the circuit must be disconnected in order to use this
type of meter. The type of unit shown is an internal shunt and
generally used for loads of 10 amps or less. Care must be taken
to not measure current greater than the meter rating. This type
of ammeter is not recommended for most of the measurements
described in this manual. However, if this is the only type
available, be sure to follow the meter manufacturer’s instructions
for connection and use.
FIGURE 1-4. In-Line Digital Ammeter
2. Figure 1-5 shows an in-line digital ammeter used to measure an
unknown current draw. An example of this might be the result of a
parasitic load. On the 10 amp scale, the current would be too low
to be measurable. However, with the meter on the 300 mA scale,
the current draw in milliamps can be read.
FIGURE 1-5. In-Line Ammeter
3. Figure 1-6 shows a clamp-on ammeter, the most common type
of current measurement described in this manual. Zero out the
meter before using and make sure the jaws are completely closed
during use. Place the meter jaws around the cable, with the arrow
points in the direction of current flow, to measure all the current.
10A
10 AMPS OR LESS LOAD DP-1009
UNKNOWN
CURRENT
DRAW
DP-1010

delcoremy.com Page 5
CLAMP-ON
TYPE AMMETER
DP-1011
FIGURE 1-6. Clamp-On Type Ammeter
1-20. MEASURING RESISTANCE WITH THE OHMMETER. The
ohmmeter is used to measure electrical resistance. The unit of
measure is the ohm. The ohmmeter is connected across the unit
or portion of the circuit for which the resistance is to be measured.
The ohmmeter has its own power source, usually a small battery,
which causes current to flow through the circuit to be measured.
Since the meter power source (battery) voltage is known, the
current is inversely proportional to the resistance of the circuit.
The meter automatically computes and reads out the resistance:
E (voltage) divided by I (current) equals R (resistance).
1-21. OHMMETER SELECTION. As with voltmeters and ammeters,
both analog (needle) and digital ohmmeters are available. Digital
ohmmeters are preferred for the same reasons as the others.
Additionally, most digital ohmmeters have a diode scale which can
be used to test diodes and transistors.
1-22. OHMMETER USE. Figures 1-7 through 1-9 illustrate some
typical uses of the ohmmeter.
CAUTION
Typical heavy duty electrical system voltage (12 or 24-volts)
could produce a current flow through the ohmmeter that could
damage the meter. Never connect an ohmmeter to a circuit that
is under voltage. Always disconnect the battery ground cable
before using the ohmmeter.
1-23. As shown in Figures 1-7 and 1-8, the ohmmeter also is
useful as a continuity meter. An infinite ohmmeter reading (See
Figure 1-7) indicates an open circuit (no continuity). A very low
(approaching zero) reading (See Figure 1-8) indicates continuity.
Figure 1-9 illustrates some digital ohmmeter applications.
FIGURE 1-7. Analog Ohmmeter Showing
Open Circuit
NOTE
Most digital meters have a diode scale ( ) which must be
used to check diodes or transistors rather than the ohm scale.
1-24. APPLYING AN ELECTRICAL LOAD WITH A CARBON PILE.
(See Figure 1-10) The carbon pile is a variable resistor designed
to carry high current. A carbon pile, along with a voltmeter and
ammeter, is normally an integral part of a modern battery tester.
In addition to load testing batteries, carbon piles are used to test
starter and alternator circuits.
FIGURE 1-8. Analog Ohmmeter Showing
Continuity
TOUCHING
GROUND
OHMMETER
OPEN
OHMETER
DP-1012
TRUCK
FRAME
DP-1013

Page 6
EXAMPLES
DP-1014
.4502.3
0.00
COIL DIODE
DIGITALDIGITAL
OL
FIGURE 1-9. Digital Ohmmeter
CAUTION
On 24-volt systems, use only a carbon pile specifically designed
for 24-volt use. A 12-volt carbon pile could be damaged if used
in a 24-volt circuit.
1-25. THE BASIC HEAVY-DUTY ELECTRICAL SYSTEM. Today’s
basic heavy duty electrical system (See Figure 1-1) consists
of batteries (usually three or four, but up to eight connected),
a starter, an alternator, a magnetic switch, an ignition switch,
a push-button switch, and the required wiring. The batteries
provide the high current required by the starter. The magnetic
switch controls the battery current to the starter solenoid. The
ignition and push-button switches activate the magnetic switch,
which in turn energizes the starter. If all functions work properly,
the engine will crank.
1-26. The mechanical energy of the running engine provides the
power for the alternator. The alternator creates the electrical
energy needed to recharge the batteries and power the vehicle’s
electrical accessories and loads.
DP-1015
FIGURE 1-10. Carbon Pile
1-27. How well the electrical system components are matched
will determine in a large part how eectively and eciently the
system will operate. Another important factor in system design is
that system wiring must be adequate to carry the current required
by each circuit.
1-28. HEAVY DUTY SYSTEM BATTERIES. The battery, or batteries,
in the heavy duty electrical system are devices for storing energy.
They convert chemical energy into the electrical energy needed
to operate the starter. With the engine running, the alternator
supplies electrical energy to the batteries, which they convert into
chemical energy and store for later use.

delcoremy.com Page 7
There are three types of lead acid batteries used in commercial
vehicle applications today: the maintenance-free flooded
electrolyte battery, the AGM battery, and the Thin Plate Pure Lead
(TPPL) AGM battery. Unlike maintenance-free, flooded, lead acid
batteries that have liquid electrolyte, an AGM battery contains
a glass mat separator made of fiberglass that is placed between
each plate to absorb the electrolyte.
Fleets should prevent batteries from becoming deeply
discharged—dropping to less than 10 volts due to extended
storage with vehicle support loads. Also, trying to start trucks
with a low state of charge or weak capacity batteries can cause
high amperages and low voltages. This can overheat the starter
motor and damage battery cables.
A voltmeter on the battery terminals will indicate the battery’s
State of Charge (SOC).
State of Charge Flooded
Battery
AGM
Battery
TPPL AGM
Battery
100% 12.70+ 12.80+ 12.84+
75% 12.40 12.60 12.50
50% 12.20 12.30 12.20
25% 12.00 12.00 11.90
0% 11.80 11.80 11.50

Page 8
PRELIMINARY DIAGNOSIS FLOW CHART
2-1. OVERCHARGE SYMPTOMS
• High voltmeter readings
• Battery smells bad
• Battery spews acid or smells
• Bright or burned out lights
INTERNAL VOLTMETER
REPLACE ALTERNATOR
RUN ENGINE APPROX 2000RPM
CHECK VOLTS AT ALTERNATOR
EXTERNAL REGULATOR
USE REG. SVC. BULLETIN
TO ISOLATE DEFECT
VERIFY COMPLAINT
REPAIR VOLTMETER
RETEST WITH COOL,
CHARGED BATTERIES
REPLACE DEFECTIVE
BATTERY
COMPLETE
CHECK DASH
VOLTMETER
CHECK BATTERY
TEMPERATURE
TEST BATTERIES
(PAGE 3-1)
COMPLETE
119˚F OR
LESS
120˚F OR MORE
DEFECTIVE
LESS
THAN 15.5 V
DEFECTIVE
OK
OK
MORE
THAN 15.5 V
SECTION II
Diagnosis Flow Charts

delcoremy.com Page 9
PRELIMINARY DIAGNOSIS FLOW CHART
2-2. UNDERCHARGE SYMPTOMS
• Slow or no cranking
• Low voltmeter reading
• Dim lights/slow turn signal flashers
START VEHICLE
CHECK ALTERNATOR
VOLTAGE & OUTPUT
(PAGE 19)
TIGHTEN BELT TO
MANUFACTURER
TENSION SPECS
CHECK STARTER
SOLENOID CIRCUIT
(PAGE 14)
REPAIR WIRING
CIRCUIT - VERIFY
REPAIR
CHECK DRIVE BELT
VERIFY COMPLAINT
TEST BATTERIES
(PAGE 11)
CHECK CRANKING
CIRCUIT
(PAGE 12)
REPAIR AND VERIFY
REPAIR
SEE STARTER
REPLACEMENT
DETERMINATION
(PAGE 17)
CHECK PULLEYS FOR
LOCKED BEARINGS
REPAIR DEFECTIVE
COMPONENT
REPLACE BELT
CHARGE BATTERIES
CRANK ENGINE
CHECK ALTERNATOR
VOLTAGE & OUTPUT
(PAGE 19)
SLOW
OK
OK
OK
LOCKED
DEFECTIVE
OK
OK
OK
DEFECTIVE
OK
OK BUT
DISCHARGED
MISSING
LOOSE

Page 10
PRELIMINARY DIAGNOSIS FLOW CHART
2-3. MILLED PINION SYMPTOMS
• Starter spins / no-crank
• Click / no-crank (may be intermittent)
VERIFY COMPLAINT
VISUALLY CHECK
RING GEAR
CHECK STARTER PER
APPROPRIATE
SERVICE BULLETIN
REINSTALL STARTER AND
PERFORM CIRCUIT CHECKS
(SEE PAGE 3-4)
REMOVE STARTER –
VISUALLY CHECK PINION CHECK AND REPAIR SOLENOID CIRCUIT
REPAIR VERIFIED
REPAIR OR REPLACE
STARTER
(DO NOT INSTALL)
REPLACE RING GEAR
AND CHECK FLANGE
TO FLYWHEEL DIM
REPLACE STARTER
AND VERIFY REPAIR
CONNECT VOLTMETER
FROM SOLENOID “S”
TERMINAL TO GROUND –
ENGAGE START SWITCH
DEFECTIVE
OK
MILLED TEETH
OK
OK
OK
SYMPTOMS CONTINUE
MILLED PINION
MORE THAN 6.0 V NO VOLTS

delcoremy.com Page 11
3-1. TESTING FLOODED LEAD ACID
MAINTENANCE FREE BATTERIES WITH
A HYDROMETER EYE
CAUTION
When handling batteries, wear face or eye protection and
provide good ventilation. Have a water supply available, and
keep away from fire, flame or sparks.
3-2. TEST PROCEDURE.
Disconnect
NOTE
If battery has threaded terminals, use terminal adapters or verify
you are testing on the lead pads not the threaded terminals.
Testing using the studs can create a false bad battery reading.
NOTE
If you are using an hand held electronic tester, then follow the
instructions provide with the tester.
Inspect
1. Each battery visually for damage.
2. Battery hydrometer eye.
• If battery has no hydrometer eye, proceed to step 3.
• Eye shows green, proceed to step 3.
• Eye shows dark, recharge battery, then proceed to step 3.
• Eye shows yellow, replace battery.
3. Apply 300 amp load to battery for 15 seconds and turn o
load. Wait one minute.
4. If battery has no hydrometer eye, measure terminal voltage:
Test
a. If 12.4 volts or more, continue test.
b. If less than 12.4 volts, recharge battery, and repeat steps
3 and 4.
Test
5. All batteries passing previous inspection or test as follows:
a. Apply test load of 1\2 CCA rating at 0˚F in amps.
b. After 15 seconds with load on, measure and record battery
terminal voltage.
c. Turn load o.
d. Estimate battery temperature and check recorded voltage
against following table.
Temp. F 70 50 30 15 0
Min. Volts 9.6 9.4 9.1 8.8 8.5
e. If recorded voltage does not meet or exceed that in table,
replace battery. Otherwise, battery is okay.
3-3. TEST COMPLETION.
Clean
1. Cable ends and battery terminals with wire brush.
Tighten
1. Battery hold-downs to specifications.
NOTE
Leave battery cables disconnected and proceed with wiring
tests.
ST1201 ADAPTER
PRIMARY BATTERY
CONNECTION AREA
STUD TERMINAL
DP-1019
FIGURE 3-1. Testing Batteries
3-4. TESTING BATTERIES
CAUTION
When handling batteries, wear face or eye protection and
provide good ventilation. Have a water supply available, and
keep away from fire, flame or sparks.
SECTION III
Diagnostic Testing

Page 12
3-5. TEST PROCEDURE
Disconnect
NOTE
If battery has threaded terminals, use terminal adapters or verify
you are testing on the lead pads not the threaded terminals.
Testing using the studs can create a false bad battery reading.
NOTE
If you are using an hand held electronic tester, then follow the
instructions provide with the tester.
Inspect
1. Each battery visually for damage.
2. Electrolyte level.
• If fluid is above top of plates in all cells, proceed to step 3.
• If fluid is not above top of all plates, add water as required
and charge battery for 15 minutes at 15-25 amps to mix
electrolyte. Then proceed to step 3.
3. Electrolyte specific gravity with hydrometer at 80˚ F. Readings
for all cells should not be less than 1.230. The dierence between
high and low reading should not exceed 0.050.
• If battery meets above requirements, proceed to next test.
• If readings show a dierence of more than 0.050, replace
the battery.
• If readings show less than 0.050 dierence but one or
more cells read less than 1.230, recharge the battery.
Remove
1. All battery caps.
Test
2. Apply 300 amp load to battery for 15 seconds and turn o
load.
3. If blue haze is seen in any cell, replace battery. Otherwise,
proceed with next test.
Test
1. All batteries passing previous inspections or tests as follows:
a. Measure and record electrolyte temperature and replace
vent caps.
b. Apply test load of 1\2 CCA rating at 0˚F in amps.
c. After 15 seconds with load on, measure and record battery
terminal voltage.
d. Turn load o.
e. Check recorded voltage against following table for
electrolyte temperature.
Temp. F 70 60 50 40 30 20 10 0
Min. Volts 9.6 9.5 9.4 9.3 9.1 8.9 8.7 8.5
f. If recorded voltage does not meet or exceed that in table,
replace battery. Otherwise, battery is okay.
3-6. TEST COMPLETION.
Clean
1. Cable ends and battery terminals with wire brush.
Tighten
1. Battery hold-downs to specifications.
NOTE
Leave battery cables disconnected and proceed with wiring
tests.
FIGURE 3-2. Testing Batteries
3-7. BATTERY CABLE TEST WITH
SINGLE BATTERY LOCATION
(SEE FIGURE 3-3)
CAUTION
If the vehicle has a combination 12/24-volt system using a series-
parallel switch or a T/R alternator, do not use this procedure.
Contact BorgWarner Technical Support at 800-372-0222 or email
[e-mail] for information on such systems.

delcoremy.com Page 13
Slow or sluggish cranking may be caused by high resistance in the
battery cables or connections, especially in cold weather. After all
batteries test well and the terminals are clean, check the battery
cables. This involves placing an adjustable carbon pile load on the
batteries at the starter and then measuring the voltage drop in
each cable. The voltage drop in the positive cable plus the voltage
drop in the negative cable equals the total drop or the dierence
between the battery voltage and the starter voltage.
3-8. TEST PROCEDURE.
NOTE
For a 24-volt system, use a 24-volt carbon pile. As an
alternative, connect only one 12-volt battery to the system
(disconnect all other batteries). Test at 12-volts but use the
amperage specified for a 24-volt system. Immediately upon
completion of tests, reconnect batteries in the approved manner
for a 24-volt system.
Connect
CAUTION
Starter solenoid BAT terminal is at battery voltage when
batteries are connected.
1. Positive carbon pile lead to starter solenoid BAT terminal.
2. Negative carbon pile lead to starter ground terminal.
3. Battery cables (see NOTICE above) if not already connected.
NOTE
At starter, make voltmeter connection to terminal—not to
carbon pile clamp.
4. Low scale digital voltmeter from starter solenoid BAT terminal
to battery positive.
Test
1. Turn on carbon pile and adjust load to 500 amps (250 amps
for 24-volt system).
2. Read and record positive cable voltage drop (V4), then turn o
carbon pile.
Connect
NOTE
At starter, make voltmeter connection to terminal—not to
carbon pile clamp.
1. Low scale digital voltmeter from starter ground terminal to
battery negative.
Test
1. Turn on carbon pile and adjust load to 500 amps (250 amps
for 24-volt system).
2. Read and record negative cable voltage drop, (V5) then turn
o carbon pile.
3. Add positive cable loss (V4) and negative cable loss (V5) to
get total cable loss (V3). This loss (V3) shall not exceed:
• 12-volt system with 37MT, 40MT, 41MT or 42MT starter — 0.500
volt maximum voltage loss
• 12-volt system with 50MT starter — 0.400 volt maximum loss
• 24-volt system with 37MT, 40MT, 41MT, 42 MT, or 50 MT starter
— 1.000 volt
4. Replace cables or repair circuits with excessive voltage drop.
3-9. TEST COMPLETION. If temporary 12-volt test connections
were made for 24-volt systems, reconnect batteries to vehicle
specifications for 24-volt operation before starting vehicle.
However, if the tests following are to be performed, keep the
temporary 12-volt hook-up.
FIGURE 3-3. Battery Cable Test –
Typical 12-Volt System

Page 14
3-10. BATTERY CABLE TEST WITH
DUAL-BATTERY LOCATIONS
(SEE FIGURE 3-4)
This test applies if the vehicle has more than one battery location
and the batteries are connected to the starter by separate cables.
Essentially, this is the same as the previous test with a single
battery location (paragraphs 3-7 through 3-9) except as follows:
3-11. TEST PROCEDURE (See Figure 3-4).
NOTE
If the system usually operates on 24-volts, connect one battery
at each location to the starting motor, making a temporary 12-
volt system.
1. Disconnect batteries from first set.
2. Test second set cables as described in paragraph 3-8 except
apply 250 amp load at starter (125 amp for 24-volt system).
3. Use same voltage drop or loss limits as specified in paragraph
3-8.
4. Reconnect first set of batteries and disconnect second set.
5. Repeat steps 2 and 3 for first set of cables.
6. Replace cables or repair circuits with excessive voltage drop.
3-12. TEST COMPLETION. If temporary 12-volt test connections
were made for 24-volt system, reconnect batteries to vehicle
specifications for 24-volt operation before starting vehicle.
However, if the tests following are to be performed, keep the
temporary 12-volt hook-up. CARBON PILE
POSITIVE
VOLTAGE
LOSS
NEGATIVE
VOLTAGE
LOSS
FIRST SET
SECOND SET
FIGURE 3-4. Battery Cable Test -
Typical Dual Box 12-Volt System
3-13. STARTER SOLENOID CIRCUIT
TEST
The starter shifting in and out, or not pulling in, is often caused by
high resistance in the starter solenoid circuit. When the solenoid
circuit has excessive voltage loss, the starter pinion may not
engage the flywheel. If it does engage, it may drop out too soon
when battery voltage lowers. The solenoid circuit usually consists
of a magnetic switch with leads to and from the starter solenoid.
Some vehicles use only a push-button switch to control the starter
solenoid and this same test applies.

delcoremy.com Page 15
NOTE
For starters with an integral magnetic switch, use the test
procedures specific to those starters.
NOTE
When testing 24-volt systems, use the same temporary 12-volt
connection as for the Battery Cable Test, paragraph 3-7.
3-14. SOLENOID CIRCUIT VOLTAGE LOSS TEST (See Figure 3-5).
Disconnect
1. Lead to S terminal on starter solenoid.
Connect
1. Carbon pile to switch wire lead and to starter ground terminal
(a small clamp or jumper wire may be helpful).
2. Positive lead of digital voltmeter set on low scale to solenoid
BAT terminal.
3. Negative lead of voltmeter to switch wire lead to which
carbon pile is connected. Meter will show battery voltage.
NOTE
In the following step, if the magnetic switch does not close on a
12-volt vehicle, perform Magnetic Switch Circuit Test, paragraph
3-18, then return to this point in the Starter Solenoid Circuit
Test.
NOTE
In the following step on a 24-volt vehicle, if the temporary
12-volt system will not close the magnetic switch, bypass it
with a heavy jumper connected between the two large studs
on the magnetic switch. Electrically this does the same thing
as pushing the button and closing the switch. With no button
to release, the jumper must be disconnected after each voltage
reading.
Test
1. Have assistant push starter button with key on. Listen for
sound of magnetic switch closing. Voltmeter reading should be
zero.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if 24-
volt system).
3. Read and record voltage (V6) onvoltmeter.
4. Voltage loss shall not exceed:
12-volt system - 1.0 volt
24-volt system - 2.0 volt
5. If circuit voltage loss is less than maximum, solenoid circuit
is okay, turn o and disconnect carbon pile and proceed to
Magnetic Switch Circuit Test, paragraph 3-18. If voltage loss
exceeds maximum, loss is excessive. This may be caused by
loose terminals, corrosion, too small a wire, switch located too far
from starter, or worn out magnetic switch. Perform Wiring Test,
paragraph 3-15, and Magnetic Switch Contactor Test, paragraph
3-16, to isolate the problem.
VOLTAGE (6)
CARBON PILE
FIGURE 3-5. Starter Solenoid
Circuit Test
3-15. WIRING TEST (See Figure 3-6). With carbon pile connected
as instructed in previous Starter Solenoid Circuit Test, proceed as
follows:
Connect
1. Plus lead of digital voltmeter set on low scale to solenoid BAT
terminal.
2. Minus lead of voltmeter to a large terminal on magnetic
switch. If voltage shows, reconnect lead to other large terminal on
magnetic switch.
NOTE
In the following step, on a 24-volt vehicle, if the temporary
12-volt system will not close the magnetic switch, bypass it
with a heavy jumper connected between the two large studs
on the magnetic switch. Electrically this does the same thing
as pushing the button and closing the switch. With no button
to release, the jumper must be disconnected after each voltage
reading.

Page 16
Test
1. Push starter button with key on.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V9) onvoltmeter.
Connect
1. Positive lead of digital voltmeter set on low scale to switch
wire lead to which carbon pile is connected.
2. Negative lead of voltmeter to other large terminal on
magnetic switch.
Test
1. Push starter button with key on.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V10) on voltmeter.
4. Add voltage loss (V10) to voltage loss (V9), previously
recorded, to get total wire voltage loss.
5. Total wire voltage loss shall not exceed:
12-volt system - 0.8 volt
24-volt system - 1.8 volt
6. Replace and repair wiring and connections if voltage loss is
excessive.
NOTE
Perform the following test only if the magnetic switch closed in
preceding tests.
3-16. MAGNETIC SWITCH CONTACTOR TEST (See Figure 3-6).
With carbon pile connected as instructed in previous Starter
Solenoid Circuit Test, proceed as follows:
Connect
1. Digital voltmeter set on low scale across large terminals of
magnetic switch. Battery voltage will show immediately.
Test
1. Push starter button with key on. Voltage will read zero.
2. Turn on and adjust carbon pile to 100 amp load (60 amp if
24-volt system).
3. Read and record voltage (V11) across magnetic switch on
voltmeter, then release starter button.
4. Magnetic switch contactor voltage loss (V11) shall not exceed
0.2 volts for 12- or 24-volt system.
5. Replace magnetic switch if contactor voltage loss is excessive.
DP-1024
CARBON PILE
SECOND WIRE LOSS (10)
CONTACTOR
LOSS (11)
FIRST
WIRE
LOSS (9)
FIGURE 3-6. Solenoid Circuit Wiring
and Contactor Test
3-17. TEST COMPLETION. Turn carbon pile o. Remove
carbon pile and voltmeter from circuit. Leave solenoid S wire
disconnected and temporarily taped for insulation at the terminal.
3-18. MAGNETIC SWITCH CIRCUIT TEST
This test must be performed using full voltage of the system. If
a 24-volt system was temporarily connected to a 12-volt system
for a previous test, proceed to the Alternator Wiring Test,
paragraph 3-26. Then, return to this test after the batteries have
been reconnected to the 24-volt system. Note that the lead to
the S terminal on the starter solenoid remains disconnected from
previous tests (See Figure 3-7).

delcoremy.com Page 17
3-19. TEST PROCEDURE.
NOTE
Magnetic switch that does not close or drops out too soon
can be caused by high resistance or open circuit in the control
circuit.
NOTE
Leave the S lead disconnected to prevent engine from cranking
during these tests.
Connect
1. Digital voltmeter set on battery voltage scale to two small
terminals on magnetic switch. If magnetic switch has only one
small terminal, use switch bracket for other connection.
Test
1. With key on, push start button. Listen for click that signifies
magnetic switch closing. Note and record voltmeter reading V(13).
2. If magnetic switch closed (click detected or voltage at both
large switch terminals) and voltage V(13) is within 1.0 volt (2.0
volts for 24-volt system) of battery voltage V(12), this circuit is
okay.
3. If magnetic switch does not close and voltage V(13) is within
1.0 volt (2.0 volt for 24-volt system) of battery voltage V(12),
replace magnetic switch and retest.
4. If voltage V(13) is more than 1.0 volt (2.0 volt for 24-volt
system) below battery voltage, move the voltmeter lead on the
magnetic switch ground to frame or motor ground terminal. With
key on, push start button and read voltage V(14). If voltage V(14)
is within 1.0 volt (2.0 volts for 24-volt system) of battery voltage,
repair magnetic switch ground lead or connections. If not, replace
voltmeter ground lead at magnetic switch ground terminal.
5. Repeat step 4, moving voltmeter plus lead to the following
locations and measuring the specified voltages with the key on
and the push-button depressed.
If any voltage is not within 1.0 volt (2.0 volts for 24-volt system) of
battery voltage, repair or replace the wire or component specified
and retest:
V(15)-wire between push-button and magnetic switch
V(16) push-button
V(17) wire between push-button and key switch
V(18) key switch
V(19) wire between key switch and solenoid BAT terminal
3-20. TEST COMPLETION. Remove voltmeter from vehicle. If
all tests have been completed satisfactorily, reconnect lead to S
terminal on starter solenoid so that engine can be started.
PUSH
BUTTON
MAGNETIC
SWITCH
VOLTAGE (13)
V(15)
V(16)
IGNITION
BATTERY
CABLE
VOLTAGE (12)
V(19)
V(14)
V(17) V(18)
DP-1025
FIGURE 3-7. Magnetic Switch
Circuit Test
3-21. STARTER REPLACEMENT
DETERMINATION
Up to this point, the batteries and starter wiring have been
checked. The following additional checks should be made before
considering starter replacement, and finally, the criteria for starter
replacement, if necessary.
3-22. COLD WEATHER CRANKING. Starter circuits with a
magnetic switch also can fail to hold during cold weather starting
and low voltage, even though the switches and circuits tested
okay at higher temperatures. This condition will sound as though
the starter is failing to stay engaged with the engine. It is caused
by the cold weather low voltage of the system releasing the
electrical connection of the magnetic switch. To test for this
condition, proceed as follows:
Test
CAUTION
Large terminal studs on magnetic switch are at battery voltage.
Engine should crank when jumper is connected.
1. With key switch on, press start button and have assistant
clamp heavy battery jumper cable between two large studs on
magnetic switch. Engine should crank.
2. Immediately remove jumper to stop engine cranking.
3. If engine starts with jumper in place, replace magnetic switch.

Page 18
4. If vehicle now starts properly, make sure starter mounting bolts
are tight and proceed to Alternator Wiring Test.
3-23. AVAILABLE CRANKING VOLTAGE. If batteries, switches and
wiring have been checked and starter still cranks slowly, check for
available voltage at the starter while cranking. Proceed as follows:
Test
1. Have assistant press push-button with key switch on while
measuring voltage across solenoid BAT terminal and starter
ground terminal.
2. If voltage is 9.0 volts (18 volts for 24-volt system) or less while
cranking, check battery interconnecting cables as specified in
next step.
3. Measure voltage across each battery while cranking. Touch
voltmeter leads to terminals of every battery. If dierence
between any two battery readings in same box is more than 0.5
volt, or if any cable or connection feels warm to the touch, check
or replace interconnecting cable(s) as required.
3-24. RING GEAR AND PINION CHECK. One final check before
replacing the starter is to inspect the pinion and ring gear.
Inspect
1. Pinion and ring gear visually while assistant bars engine over.
Be sure to check entire ring gear.
2. If pinion is damaged, replace starter. If ring gear is damaged,
replace ring gear and note that there is a likelihood the pinion also
may be damaged.
3-25. STARTER REPLACEMENT. After making all tests specified,
if the vehicle does not crank properly, the problem is with the
starter or engine. Replace the starter and re-check to see if engine
cranks properly. If not, then look for a mechanical problem with
the engine.
3-26. ALTERNATOR WIRING TEST
This procedure is the first step in checking out the charging
system: output of the alternator, batteries and accessory loads
with a minimum of voltage loss. Any loss slows the rate of charge
to the batteries and could cause the batteries to be partially
discharged. Discharged batteries can result in starter damage.
Low output voltage can cause improper performance of other
vehicle electrical components.
3-27. TEST PROCEDURE (See Figure 3-8). Instead of using the
alternator output, this test uses the same current but draws it
from the batteries. Using a carbon pile load, current flows in
reverse through the circuit with the engine o. Proceed as follows:
NOTE
24-volt systems must be connected to a temporary 12-volt
configuration as described for Battery Cable Test, paragraph
3-8.
NOTE
Before proceeding with this test, make sure that the batteries
have been tested and that the terminal has been cleaned and
tightened.
CAUTION
Alternator output terminal is at battery voltage. Engine must be
o for this test.
Connect
1. Carbon pile to alternator output terminal and to ground.
NOTE
Jumper wires may be used to extend voltmeter leads if
necessary.
2. Digital voltmeter set on low scale from alternator output
terminal to positive battery terminal.
Test
1. Turn on and adjust carbon pile to alternator-rated amperage
output.
2. Read voltmeter and record voltage (V24), which is positive
circuit voltage loss. Immediately turn o carbon pile.
Connect
1. Digital voltmeter set on low scale from alternator ground to
negative battery terminal.
Test
1. Turn on and adjust carbon pile to alternator rated amperage
output.
2. Read voltmeter and record voltage (V25), which is negative
circuit voltage loss. Immediately turn o carbon pile.
3. Add positive circuit loss (V24) and negative circuit loss (V25)
to get total system loss (V23). This loss (V23) shall not exceed:
• 12-volt system - 0.500 volt maximum voltage loss
• 24-volt system - 1.000 volt maximum voltage loss
4. Replace cables or repair circuits with excessive voltage loss.