BENDIX MC-12 MODULATOR CONTROLLER ASSY User manual

1
®
SD-13-4762
Bendix®MC-12™Modulator Controller Assembly
FIGURE 1 - MC-12™MODULATOR CONTROLLER ASSY. wheel end send wheel speed information to the EC-12™
controller through the 14 pin connector. The sensors are
actuallyAC.generators.They house magnets,whichcreate
amagneticfield.Whenthefieldisinterruptedbyanirregular
surface, such as a tone ring,AC. voltage is produced. The
frequencyofvoltageincreasesordecreasesaswheelspeed
increasesor decreases.
Duringnormal,nonantilockoperation,theM-12™modulator's
inlet solenoid is open, and the exhaust solenoid is closed.
Inthiscondition,theM-12™modulator functionsasaregular
R-12™relay valve. It receives a control signal from the foot
valve, which passes through the open inlet solenoid and
causes the brakes to apply in proportion to the amount of
controlpressure.
If wheel lock up is impending, the EC-12™controller
commands the solenoids to modulate brake chamber
pressure on the axle(s) in which the system is installed.
The MC-12™modulator/controller receives its power from
the vehicle's stop light circuit (pin 4 on the standard seven
pinconnector—red).ThepowerenterstheEC-12™controller
at pin A and (optionally) pin B from the auxiliary terminal
(bluewire) of thetrailer’s7pin connector.
DESCRIPTION
The Bendix®MC-12™modulator trailer antilock system is
designedtoimprovevehiclestabilitybyreducingwheellock
upduringaggressivebraking.LikeBendix'stractorantilock,
thetrailersystemcanprovidesingleor tandem axle control.
The main component is nipple mounted to a reservoir, so
the system requires no special trailer modifications.
The trailerantilocksystemconsists ofthe following: MC-12™
modulator/controller, WS-20™wheel speed sensors,
electricalconnectors and wiring.The MC-12™modulator is
the main component. It houses the EC-12™electronic
controllerandtheM-12™modulator,whichcontainssolenoids
andastandardrelayvalve.
TheEC-12™controller houses theelectronicsthat regulate
thetrailerantilocksystemandalsoincorporatesa diagnostic
displaywindow and a14 pin connector.
TheEC-12™controllermountsto the M-12™modulatorwith
fourbolts, and itis internallyconnected to thesolenoids by
afourpinconnector.Thesolenoidsaretheinterfacebetween
the EC-12™controller electronic signals and the
pneumaticallyoperatedmodulator.Sensorsmountedatthe
DIAGNOSTIC
DISPLAY DIAGNOSTIC
DISPLAY
DELIVERY
PORTS
(2 VERTICAL
2
HORIZONTAL)
CONTROL
PORT
14 PIN
CONNECTOR
EC-12™
CONTROLLER
M-12™
MODULATOR
DELIVERY
PORTS
(4VERTICAL)

2
FIGURE 2 - MC-12™MODULATOR TRAILER SYSTEM WIRING SCHEMATIC
Seven Conductor Antilock Wire Gauge
Pin (Wire Connector Wire Single/
Connector No.) Letter Color Lamp and Signal Circuits Dolly Double Triple
1 1 C White Ground Return To Towing Vehicle 12 10 8
2 2 - Black Clearance, Side Marker and Identification Lamps 12 12 12
3 3 - Yellow Left Hand Turn Signal and Hazard Signal Lamps 12 12 12
4 4 - Red Stop Lamps 10 10 10
5 5 - Green Right Hand Turn Signal and Hazard Signal Lamps 12 12 12
6 6 - Brown Tail, Clearance, Side Marker and License Plate Lamps 12 12 12
7 7 B* Blue Auxiliary, Dome, Etc. or constant Antilock power 12 12 12
4 9 A Red Antilock Power From Stop Lamp 10 10 10
- 8 D Yellow Trailer Mounted Status Light 14/16 14/16 14/16
- 10/11 N/P - Wheel Speed Sensor 16/18 16/18 16/18
- 12/13 M/L - Wheel Speed Sensor 16/18 16/18 16/18
* Antilock Connector Pin B is an option and is used to provide constant power to the MC-12™modulator during trailer operation.
Trailer
Mounted
Status
Indicator
Marker Marker
Marker Marker
Clearance
Clearance
Wheel
Speed
Sensor
Marker
Marker
Rear7 Pin
Connector
Plug(See
Note)
Wheel
Speed
Sensor
CI/Directional
CI/Directional
Stop & Tail
Stop & Tail
LicensePlate
Note:
The rear 7 pin connector plug is for Dolly operations for Doubles & Triples
To Pin “G” on
MC-12™Modulator
Connector
ToPower Sideof
TractorIgnition
TractorElectrical
Relay
TractorDashMounted
TrailerAntilockStatus
Lamp
The relay illustrated to the right is used when
a tractor, dash mounted status lamp for the
trailer antilock system is desired. Like the
trailer mounted status lamp, this is an option
and is not required.

3
System ground (pin 1 on the seven pin connector—white)
enters the MC-12™modulator at pin C.
Eachwheel speed sensorsendsthe MC-12™modulator its
AC. signal through a pair of wires. The MC-12™modulator
pins for the sensors are L-M and N-P.
TheMC-12™modulatorcansenda+12vfailuresignaltothe
optionaltrailermountedstatuslightthroughpinD.Thestatus
lightindicates the conditionofthe trailer antilock system.In
addition,theMC-12™modulatorcansendagroundingsignal
throughitspinJ to anoptionaltractor, dash mountedstatus
lamp. Duringstartup,whenthetrailerbrakesareactuated,
trailer antilock immediately runs a self check. The status
lightflashesonceandthengoesoff.Shouldaproblemoccur,
the antilock system disengages and returns to normal
R-12™relayvalveoperation.
Ifthe status lightcomeson and remainsonwhen the trailer
brakes are actuated, a system problem has occurred. The
EC-12™controller contains a diagnostic window, which
FIGURE 3 - SPEED SENSOR VOLTAGE CYCLE OUTPUT
PEAK TO PEAK
PEAK TO PEAK
HIGHSPEED
LOWSPEED
directs the driver to the problem area.Aseries of LEDs on
theEC-12™controller indicate thestatusof power, EC-12™
controller,wheelspeedsensors,M-12™modulatorsolenoids,
orvoltagelevel.
OPERATION
APPLYING: Normal Service Application
When a normal service brake application is made, and the
EC-12™controllerdoesnotsense impending wheel lock up,
controlairpressurefromthebrakevalveentersthemodulator
control port. The air passes through the supply solenoid
and acts on the modulator's piston. The piston closes the
modulatorexhaustandopenstheinlet,deliveringsupply air
outthe delivery ports.
FIGURE 4 - APPLYING: NORMAL SERVICE APPLICATION
DELIVERY
PISTON
EXHAUST
SUPPLY
EXHAUST
SOLENOID
CONTROL
DOUBLE
CHECK
TRAILER
CONTROL
BRAKE
VALVE
SUPPLY
SOLENOID
SERVICE
BRAKE
CHAMBER

4
BALANCED POSITION: Normal Service Application
The modulator reaches a balanced position when control
pressureacting upon thetopside of thepistonapproaches
that of the air acting upon the underside of the piston. The
piston moves upward and closes the inlet valve, while the
exhaustremains closed. Thisprevents the modulatorfrom
deliveringorexhaustingair.
EXHAUSTING: Normal Service Application
Whenthebrakevalveisreleased,controlpressureexhausts
through the supply solenoid and the check valve in the
solenoidhousingandouttheexhaustportofthebrakevalve.
Asthepistonmovesupward,themodulator'sexhaustopens,
allowingair from thepiston's underside toexhaust through
themodulator exhaust port.
ANTILOCK MODE: Solenoids Activated
If a service brake application is made and the EC-12™
controllersenseswheellockup,itwillcommandthe antilock
system to alter the service brake application.
When activated, shuttles within the solenoids alter the
applicationand exhaust ofcontrolair pressure. Thesupply
solenoidcloses,preventingcontrollinepressurefromentering
the modulator. Then the exhaust solenoid opens, allowing
control pressure to exhaust from the top side of the piston
through the exhaust port of the solenoid assembly. This
activity occurs in a pulsating manner, simulating "pumping
of the brakes."
PREVENTIVE MAINTENANCE
1. Every 3 months; 25,000 miles; or 900 operating hours
performSERVICECHECKS.
2. Everytwelvemonths; 100,000 miles;or3600operating
hours, disassemble the relay valve portion of the M-12
Modulatorandclean parts with mineralspirits.DONOT
DISASSEMBLETHE SOLENOIDASSEMBLY. Replace
allrubber parts and anypartsworn or damaged.Check
forproperoperationbeforeplacingvehiclein service.
FIGURE 5 - BALANCED POSITION: NORMAL SERVICE APPLICATION
TRAILER
CONTROL
DOUBLE
CHECK
BRAKE
VALVE
CONTROL
PISTON
DELIVERY
EXHAUST
SUPPLY
EXHAUST
SOLENOID
SUPPLY
SOLENOID
SERVICE BRAKE
CHAMBER

5
FIGURE 6 - EXHAUSTING: NORMAL SERVICE APPLICATION
FIGURE 7 - ANTILOCK MODE: SOLENOIDS ACTIVATED
EXHAUST
SUPPLY
EXHAUST
SOLENOID
CONTROL
DOUBLE
CHECK
TRAILER
CONTROL
BRAKE
VALVE
DELIVERY
PISTON
SUPPLY
SOLENOID
SERVICE BRAKE
CHAMBER
DELIVERY
PISTON
EXHAUST
SUPPLY
EXHAUST
SOLENOID
CONTROL
DOUBLE
CHECK
BRAKE
VALVE
SUPPLY
SOLENOID
SERVICE BRAKE
CHAMBER
TRAILER
CONTROL

6
SERVICE CHECKS
Ensure that all wiring and connectors are secure and free
from visible damage. Although the MC-12™modulator
assembly contains self check diagnostics, the LED (Light
EmittingDiode) display shouldbe inspected toensure that
theLEDs are functional.With the trailerbrakes actuated, a
magnet(800gauss;capableofpickingup 3 ounces) held to
theLEDresetareashouldcausealloftheLEDstoilluminate.
If one or more of the LEDs DO NOT ILLUMINATE and the
optional status light indicates proper system function, the
nonilluminatedLED(s)shouldbenotedforfuturereference.
Although the diagnostic capabilities will be limited, the
system will continue to function as designed.
TheMC-12™modulator assembly monitorsthe electronics
ofthesystemuponinitialtrailerbrake application. However,
thevehicleshouldberoadtested periodicallytoverifyproper
solenoid function. The solenoids can be tested by making
an aggressive trailer stop from a speed of 20 m.p.h. When
an antilock stop is made, solenoid pulsation creates an
audibleburst ofair, whichcan beheard from the outsideof
thetrailer.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all
times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
enginebeinoperation,EXTREMECAUTIONshould
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Useonlythe proper tools and observe
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air
systems,makecertaintodrain the air pressurefrom
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS®
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommendedprocedures,deactivatetheelectrical
system in a manner that safely removes all
electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certainallcomponentsandsystemsarerestoredto
their proper operating condition.
FIGURE 8 - ELECTRICAL CONNECTOR
A
B
C
D
E
F
G
H
J
K
L
M
N
P
SENSOR 1
SNS 1
SENSOR 2
SNS 2
SENSOR 1
SNS 1
SENSOR 2
SNS 2
OPTIONAL
TRACTOR
MOUNTED
STATUS
LIGHT
OPTIONAL
CONSTANT
POWER
(TRACTOR
IGNITION)
GROUND
STOPLIGHT
SWITCH
POWER
OPTIONAL
TRAILER
MOUNTED
STATUS
LIGHT

7
REMOVAL OF THE MC-12™MODULATOR
ASSEMBLY
1. Remove and identify all air lines connected to the unit.
2. Disconnect the 14 pin connector from the unit by
looseningitsscrewandpullingtheconnectorawayfrom
its socket.
3. Remove and save the mounting hardware connecting
theMC-12™modulatorto the vehicle.
4. Prior to disassembly, remove as much contamination
as possible from the exterior of the assembly. Be sure
to keep the contamination away from the open ports.
INSTALLATION OF THE MC-12™
MODULATOR ASSEMBLY
1. ReplacetheMC-12™modulatorassemblyonthevehicle
usingthe hardware savedduringremoval. Connect the
airlinestotheproperports,asidentifiedduringremoval.
Connect the 14 pin connector into the controller and
tightenthe screw.
DISASSEMBLY
The following disassembly and assembly procedure is
presented for reference purposes and presupposes that a
majorrebuildoftheantilockvalveisbeingundertaken.Several
replacementpartsandmaintenancekitsareavailablewhich
do not require full disassembly. The instructions provided
with these parts and kits should be followed in lieu of the
instructionspresentedhere.
CAUTION:TheMC-12™modulator may belightlyclamped
inabenchviseduringdisassembly.However,overclamping
willresult in damage,leakage, and/or malfunction.If a vise
is to be used, position the MC-12™modulator so the jaws
bearontheflatarea of the supply portanditsopposingside
of the body.
1. Remove the EC-12™controller (1) from the M-12™
modulator by removing the controller's four mounting
bolts.
2. Lift the controller off the M-12™modulator and detach
the wire harness from the base of the controller by
depressing the lock tab on the side of the connector
andpullingtheconnectorfromitssocketinthecontroller.
Removethegasket(7)fromtheEC-12™controllerbody.
NOTE:If replacement ofthe controlleronly is required,
proceed to Step 8 of assembly.
3. Removesealingring(4)fromtheprotrusiononthebottom
of the solenoid assembly.
4. Using a pair of snap ring pliers, remove retaining ring
(14). Remove the exhaust assembly (13). Remove
o-ring (12) and o-ring (11) from the l.D. and O.D.,
respectively, of the exhaust assembly.
5. Removespring(10).Removetheinlet/exhaustassembly
(8). Remove the spring seat (9) from the inlet/exhaust
assembly.
6. Using your thumb, press the piston stem and push the
piston (6) out the opposite end of the body. Remove
o-ring(5) from thepiston.
7. Discard all items that have replacement parts in the
maintenancekit.
CLEANING & INSPECTION
1. Usingmineralspiritsoranequivalentsolvent, clean and
thoroughlydryallpartstobereused.Donotallowmineral
spirits to come into contact with the ECU connector or
solenoids.
2. Inspect the interior and exterior of all parts that will be
reusedforseverecorrosion,pittingandcracks.Superficial
corrosionand/orpittingontheexteriorportionofthebody
is acceptable.
3. Inspectthe bores fordeepscuffing or gouges.
4. Inspect the pipe threads in the body. Make certain they
areclean and freeofthread sealant.
FIGURE 9 - EXPLODED VIEW
1
7
2
4
5
6
3
8
910
11 12
13 14

8
5. Inspectallair line fittingsandplugs for corrosion.Clean
allold threadsealant from thepipe threads.
Anycomponentexhibitingaconditiondescribedininspection
steps 2 to 5 should be discarded and replaced before
proceeding.
ASSEMBLY—REFER TO FIG. 9
1. Using a lubricant (Bendix Pc. No. 291126) lightly coat
allo-rings and theboresof the valvebody.
2. Installspringseat (9) ontotheinlet/exhaust valve (8)so
thatit covers therubber seatof the inlet/exhaustvalve.
Place the inlet/exhaust valve, large diameter first, into
theM-12™modulator'sbottom bore.
3. Installspring(10)overthebarreloftheinlet/exhaustvalve
(8)sothatone end ofthespringrestson the spring seat
(9).
4. Installtheo-rings(11812)intotherespectivegroovesof
the O.D. and l.D. of the exhaust assembly (13). Place
thelarge diameter ofthe exhaust assemblyagainstthe
spring (10) and compress the spring until the exhaust
assemblyenterstheboreofthebodyandthe o-ring (11)
seals against the wall of the bore.
5. Depress the exhaust assembly into the bore until it
exposes the groove for the snap ring (14). Install snap
ring (14) into its groove. Make sure it is fully seated.
6. Install o-ring (5) into its groove in the piston (6). Install
piston (6) into the M-12™modulator body. The piston
stem fits into the small hole in the center of the body.
7. Installo-ring(4)onto the protrusiononthebottomof the
M-12™modulatorsolenoidassembly.Installthesolenoid
assembly(2)ontothevalvebody.Thesolenoidassembly
will fit on the M-12™modulator body in any of four
orientations,90degreesapart.However,if clearance is
a problem, make sure the control port is not directly
above the valve's supply port, which will be nipple
mounted to a reservoir. Secure the solenoid assembly
to the valve body with the four 1/2" bolts. Torque the
bolts to 120 150 in. Ibs.
8. Install gasket (7) onto the EC-12™controller. Install the
EC-12™controller (1) as shown in Figure 9 by plugging
theelectricalconnectorfromthesolenoid assembly into
the socket in the bottom of the controller. Press in until
lock tab engages. Ensure engagement by pulling the
connectorlightly.Place the controlleronto the solenoid
assembly and secure with the four 1/2" bolts and lock
washers. Torque to 30 60 in. Ibs.
OPERATIONAL AND LEAKAGE TEST
1. Chockwheels.Fullychargeairbrakesystemandadjust
brakes.
2. Make several trailer brake applications and check for
promptapplication and releaseateach wheel.
3. Check for inlet valve o-ring leakage. With the trailer
service brakes released, coat the exhaust port and the
areaaround the retainingring with asoap solution.A1"
bubble in 3 seconds is permitted.
4. Checkforexhaustvalveleakage.Withthetrailerservice
brakes fully applied, coat the exhaust port with a soap
solution. A 1" bubble in 3 seconds is permitted. Coat
theoutside of themodulator body tocheck forsealring
leakage.No leakage ispermitted.
5. If leakage is excessive around the supply and exhaust
solenoids, replace the M-12™modulator. If excessive
leakage is detected where the solenoid assembly and
M-12™modulator body meet, replace the M-12™
modulator.Ifexcessiveleakageisdetectedattheexhaust
port,beforereplacing the M-12™modulatorperformthe
followingtest:
Place the vehicle in park by exhausting the air pressure
from the emergency side of the spring brake. Perform the
leakage check around the exhaust. If the air continues to
leakout the exhaustreplacethe M-12™modulator. If aleak
existsbetweentheemergencyandservicesidesofthespring
brake,theleakageattheexhaustwillceasewhenairpressure
is exhausted from the emergency side of the spring brake.
The air pressure will pass from the emergency side to the
servicesideofthechamber, out the service inlet and out the
M-12™modulatorexhaust.
ELECTRICAL TEST
If the status light remains on after the trailer brakes have
beenactuated,inspecttheEC-12™controllerforilluminated
LEDs. Each LED represents a specific area.
VOLT LED (red) High/Low Voltage
MOD LED (red) M-12™Modulator Failure
SNS1 LED (red) Wheel Sensor Failure
SNS2 LED (red) Wheel Sensor Failure
CONT LED (red) EC-12™Controller Failure
PWR LED (green) EC-12™Controller Power
RED LEDs INDICATE FAILURE
When the EC-12™controller senses a failure, the red LED
correspondingtothe failure modewillilluminate.Afailureis
stored in memory until the problem is repaired and the
EC-12™controller is reset. NOTE: Only the voltage LED
resets itself after the condition no longer exists.

9
TROUBLESHOOTING INFORMATION
PREPARATION FOR TESTING
Alltrailerantilock testing should beperformedwitha tractor
connectedto thetrailer.
1. Connect the tractor to the trailer and build up the air
system, on both the tractor and trailer, to governor cut
outpressure.
2. Parkthecombinationonalevelsurface.Applythetractor
parkingbrakesthenreleasethetrailerparkingbrakes
only andturn off theengine.
NOTE:Sometractorsmaynothavetheabilitytorelease
thetrailerbrakeswhilethetractorparkingbrakesremain
applied. Inthisevent,chock all wheels,buildthetractor
and trailer system to governor cut out and turn off the
enginewithout applying theparkingbrakes.
TROUBLESHOOTING
GENERAL
While the EC-12™controller diagnostic display locates a
specificproblemarea,itisstillnecessarytoconfirmwhether
the problem resides in the component itself or the wiring.
Basically the troubleshooting procedure that follows is
devoted to narrowing the problem to either the wiring or a
specific antilock component. It should be noted that ALL
TROUBLESHOOTING BEGINS BY OBSERVING THE
ANTILOCK STATUS LAMP ON THE TRAILER WHILE
PERFORMINGTHE"INITIALSTART-UPPROCEDURE"and
followingthe directions containedinthe procedure.
Besuretorecorda failurebeforeresettingthesystem.Reset
byholding amagnet (capable ofpicking up 3ounces) over
theresetlocationonthediagnosticwindow.IftheLED(s)do
not clear during a reset, check all wiring and hardware per
the troubleshooting chart (BWS 1082). During a reset, all
LEDs will illuminate until the magnet is removed.
IMPORTANT - TROUBLESHOOTING TIPS
1. Record all findings and the action taken during the
troubleshooting process. The record sheet should be
filedinthetrailermaintenancefolderforfuturereference
andcomparison.
2. No voltage or resistance tests are performed into the
EC-12™controller. All voltage and resistance tests are
performed by beginning at the wire harness half of the
connectorand movingAWAYfromthe EC-12™control-
ler toward an antilock system component (modulator,
wheelspeed sensor, etc.)
NOTHING ON
GO TO
SECTION IV
GO TO
SECTION IV
NOT ON
GO
TO SECTION IV
ONE OR BOTH ON
GO TO SECTION VIA
ON
GO TO
SECTION V
DIAGNOSTIC DISPLAY
QUICK REFERENCE
ThisindexispresentedforthebenefitofpersonnelexperiencedintroubleshootingBendix®MC-12™trailer antilock
system. Itprovides aquick referenceto specificsections thatprovide testing procedures and values.

10
STARTHERE
STATUS LAMP DOES NOT BLINK, COMES
ONAND REMAINSILLUMINATED
YES
NO
STATUS LAMP COMES ON, BLINKS AND
GOES OUT.
THE SYSTEM IS FUNCTIONING NORMALLY.
MAKE NOTES OF THE PARTS REPLACED OR
REPAIRED AND STEPS TAKEN .
AMBER STATUS LAMP
BLINKS ONCE, THEN GOES OUT
SYSTEM - OK
WITHTRAILERCONNECTEDTO
TRACTOR,TURNIGNITIONON,APPLY
TRAILERSERVICEBRAKESAND
OBSERVESTATUSLAMPMOUNTED
ONTRAILER.
NO
DIDSTATUSLAMPILLUMINATE?
GO TO SECTION I “STATUS
LAMPTESTING”
ARE STOP LAMPS
ILLUMINATED
YES
TEST FOR POWER TO THE
TRAILER AT 7 PIN CONNECTOR
NO
YES
GO TO SECTION II
“INSPECTIONFOR
ILLUMINATEDLEDS”.
Troubleshooting
INITIAL START-UP PROCEDURE
TYPICAL
LOCATIONS
FOR AMBER
STATUS LAMP
TYPICAL 7 PIN TRAILER
ELECTRICALCONNECTOR
7 PIN TRAILER CONNECTOR
CONSTANT POWER (IGNITION)
STOPLIGHTPOWER
GROUND

11
Troubleshooting
SECTION I
TRAILER STATUS LAMP TESTING
REPEATTHE “INITIAL
START-UPPROCEDURE”.
STARTHERE
USING A JUMPER WIRE CONNECT PIN A TO D THEN B
TO D. WITH THE CONNECTION IN PLACE NOTE THE
CONDITION OF TRAILER STATUS LAMP.
TRAILERSTATUS LAMPON?
NO
YES REPLACEEC-12™
CONTROLLERAND RETEST.
CHECK THE FOLLOWING IN THE ORDER PRESENTED AND
AFTER REPLACING OR TESTING EACH COMPONENT,
TEST THE STATUS LAMP OPERATION:
1. CHANGE TRAILER STATUS LAMP BULB
2. CHECK TRAILER STATUS LAMP WIRING-GROUND
3. CHECK CONTINUITY OF WARNING WIRE BETWEEN PIN
D ON THE 14 PIN CONNECTOR AND THE TRAILER STATUS
LAMPSOCKET
EC-12™CONTROLLER
WIREHARNESSCONNECTOR
WITHTRACTORIGNITIONOFF,DISCONNECT
14PINWIREHARNESSCONNECTORFROM
EC-12™CONTROLLERTHENTURNTRACTOR
IGNITIONONANDMAKEANDHOLDA BRAKE
APPLICATION.
A B C D E FG H J K L M N P
POWER A & B
TRAILERSTATUS
LAMP D

12
Troubleshooting
SECTION II
INSPECTION FOR ILLUMINATED LED's
YES YES
GOTO SECTIONIV
“TESTINGFORPOWER
TOTHEEC-12™
CONTROLLER”.
NO
NO
STARTHERE
IS GREEN, PWR, LED ILLUMINATED?
REPLACETHEEC-12™
CONTROLLER
ARE ANY RED
LED's
ILLUMINATED?
NO
ARE ANY RED LED's ILLUMINATED?
YES
NO
YES
GOTOSECTIONIV
“TESTINGFORPOWER
TOTHEEC-12™
CONTROLLER”.
NOTE AND RECORD
THE CONDITION OF
ALL RED LEDS
GO TO SECTION III “INSPECTION
FOR ILLUMINATED LEDS ”.
RED LEDs
ANYILLUMINATED?
CHECKING
"PWR" LED
WITHTRACTORIGNITIONONANDBRAKESHELD
APPLIED,INSPECT EC-12™CONTROLLERFOR
PRESENCEOF ILLUMINATEDLEDSANDRECORD.
GO TO SECTION I “TRAILER STATUS
LAMPTESTING”.
ON?
CHECKING
"VOLT" LED
ON?
IS RED “VOLT”LED ON

13
Troubleshooting
SECTION III
INSPECTION FOR ILLUMINATED LEDS
NOTE RED“CONT”LEDIN
EC-12™CONTROLLER
DIAGNOSTICSWINDOW.
STARTHERE
NO
ON?
INSPECTING "CONT"
LED
NO
IS EITHER OR BOTH RED
"SNS1" OR "SNS2" LED
ILLUMINATED?
IS RED "MOD" LED
ILLUMINATED?
YES
NO TESTING "MOD"
LED
IFANYOTHERREDLEDs
AREILLUMINATED,
REPLACETHEEC-12™
CONTROLLERANDREPEAT
THE“INITIALSTART-UP
PROCEDURE”
GO TO SECTION V
“TESTINGTHE
MODULATOR”
YES NOTE THE ILLUMINATED LEDS
AND GO TO SECTION VI "TESTING
THE WHEEL SPEED SENSOR"
ON?
ISTHIS LEDILLUMINATED? YES
ON?
TESTING "SNS1 or
SNS2"LEDs
REPLACETHEEC-12™
CONTROLLER.

14
Troubleshooting
SECTION IV
TESTING FOR POWER TO THE EC-12™CONTROLLER
TURNIGNITIONOFF, DISCONNECT14PIN
WIREHARNESSCONNECTORFROMEC-12™
CONTROLLER
STARTHERE
VOLTAGE SAME AS BATTERY
VOLTAGE? MUST BE
BETWEEN 8 AND 17 VOLTS.
RECONNECT CONNECTORTOEC-12™
CONTROLLER. CHECKTHEVEHICLE
WIRINGFORCONTINUITY. REFERTOTHE
VEHICLESERVICEMANUALANDCHECK
THEBATTERYVOLTAGE. REPAIROR
REPLACEASNECESSARYANDREPEAT
THE"INITIALSTART-UPPROCEDURE"
YES
NO
MAGNETHERE
PERFORMAMAGNETICRESETBY
PASSINGAMAGNETOVERTHE
"RESET"INEC-12™CONTROLLER
DIAGNOSTICWINDOWTHEN
REMOVEMAGNET
TURNIGNITIONOFF,(DONOTAPPLYBRAKES)
RECONNECTWIREHARNESSTOEC-12™CONTROLLER.
TURNIGNITIONON&APPLY&HOLDBRAKESON.
IS THE RED, "VOLT" LED
STILLILLUMINATED?
TURN IGNITION ON, MAKE & HOLD A BRAKE
APPLICATION AND, MEASURE VOLTAGE
BETWEEN POWER AND GROUND PINS ON
WIRE HARNESS CONNECTOR
A to C
B to C
RESETTING
EC-12™
CONTROLLER
CHECKING "VOLT"
LED
ON?
ON ?
REPLACEEC-12™
CONTROLLER
REPEATTHE
“INITIALSTART-UP
PROCEDURE”.
YES
NO
A B C D E FG H J K L M N P
POWER A & B GROUND C
EC-12™CONTROLLER
WIREHARNESSCONNECTOR

15
Troubleshooting
SECTION V
TESTING THE MODULATOR
SAME RED LED's
ILLUMINATED?
NO
YES
YES
ARE ANY RED LED's
ILLUMINATED?
INSPECTCONNECTORANDRECONNECT TO
EC-12™CONTROLLER.TURN IGNITIONON&
APPLY& HOLDBRAKESON. PASS
MAGNETOVER"RESET"ONEC-12™
CONTROLLER. REMOVEMAGNETAND
NOTE REACTIONOF REDLEDS.
ARERESISTANCE
VALUESCORRECT?
YES
REPEAT “INITIALSTART-UPPROCEDURE”.
IFTESTINGHASRETURNED
TOTHISSTEP TWICE-REPLACETHE
EC-12™CONTROLLER.
REPLACEEC-12™
CONTROLLER
NO
GO TO SECTION III
“INSPECTIONFOR
ILLUMINATEDLEDS”
ANDRETEST.
IFFAILUREPERSISTS,
REPLACETHEEC-12™
CONTROLLER.
WHITE BLACK
WHITE BLACK
M-12™MODULATOR
4PINCONNECTOR
STARTHERE
MAGNETHERE
RESETTING
EC-12™CONTROLLER
REPLACE
M-12™MODULATOR
NO
TURNIGNITIONOFFANDDONOTAPPLYBRAKES.
SEPARATEEC-12™CONTROLLERFROMTHEM-12™
MODULATOR.DISCONNECT4PINCONNECTOR
BETWEENM-12™MODULATOR&EC-12™
CONTROLLERANDTESTRESISTANCEONTHE
MODULATORCONNECTOR
BLACK to BLACK READ9 to 12OHMS
WHITEtoWHITE READ 9to 12OHMS

16
Troubleshooting
SECTION VI PART A
TESTING THE WHEEL SPEED SENSOR
STARTHERE
REPEAT THE "INITIAL START-UP
PROCEDURE
ARE ANY RED LEDs
ILLUMINATED?
GO TO SECTION III - "INSPECTION
FORILLUMINATED LEDs"
NO
YES
GOTOSECTIONVIPARTB
ANDBEGINTESTING
ANY RED LED's ON?
NO
TURNIGNITIONON&APPLY&HOLD
BRAKESON.PASSMAGNETOVER
"RESET"ONEC-12™CONTROLLER.
REMOVEMAGNETANDOBSERVE
THELEDs.
RECONNECTEC-12™CONTROLLERCONNECTOR,TURN
IGNITIONON &APPLY&HOLDBRAKESON.PASS
MAGNETOVER"RESET"ONEC-12™CONTROLLER.
REMOVEMAGNETANDOBSERVELEDs
YES
A B C D E F G H J K L M N P
M -SNS 2
L-SNS 2 N-SNS 1
P-SNS 1
TESTING SPEED SENSOR RESISTANCE
MAGNETHERE
RESETTING
EC-12™CONTROLLER
MAGNETHERE
RESETTINGEC-12™
CONTROLLER
EC-12™CONTROLLERWIRE
HARNESSCONNECTOR
TURNIGNITIONOFF,DONOTAPPLYBRAKESANDCHECKFOLLOWING:
A. REMOVECONNECTORFROMEC-12™CONTROLLERANDMEASURE
RESISTANCEBETWEENSPEEDSENSORM&LANDN&P. RESISTANCE
FORBENDIX®WS-20™SPEEDSENSORSHOULDBEBETWEEN1500-2500
OHMS. REFERTOVEHICLEMAINTENANCEMANUALIFOTHERTHANTHE
WS-20™SPEEDSENSORISINUSE. IFRESISTANCE NOTCORRECT,
DISCONNECTCONNECTORATSPEEDSENSOR. INSPECTCONNECTOR,
THENCHECKRESISTANCEBETWEENPINSON SENSOR. IFRESISTANCEIS
NOTCORRECT(BETWEEN1500-2500OHMSFORTHEBENDIX®WS-20™
SPEEDSENSOR),REPLACESENSOR,OTHERWISEPROCEEDTOSTEPB.
B. CHECK “GAP”BETWEENSPEEDSENSORANDEXCITERORTONERING.
(GAPFORBENDIX®WS-20™SPEEDSENSOR,SPEEDSENDERISBETWEEN0
-.015INCHES) IFSENSORGAPMUSTBEADJUSTED,CHECKFORLOOSE
ORWORNWHEELBEARINGSBEFORERE-GAPPINGSENSOR. REFERTO
VEHICLEMAINTENANCEMANUALFORWORNBEARINGS.
C. IFSENSORGAPISCORRECTCHECKWHEELBEARINGFORFREEPLAYTO
VERIFYITCOMPLIESTOMANUFACTURER’SRECOMMENDATIONS.
D. MAKECERTAINEXCITERORTONERINGISINPLACEANDINSPECT
CONDITION. CHECKFORMISSINGORDAMAGEDTEETHANDTHATITRUNS
TRUEANDPERPENDICULARTOSENSORFACE.
E. CHECKWIRINGHARNESSANDCONNECTORSTHATRUNTOSENSOR.
F. CHECKFORDRAGGINGBRAKES(OVERADJUSTED,TRAPPEDAIRIN
ACTUATOR,OUTOFROUNDDRUMS,FAULTYRETURNSPRINGS,PARKING
BRAKESYSTEMFAULTS,ETC.)ANDCORRECTANDRETEST.

17
Troubleshooting
SECTION VI PART B
TESTING THE WHEEL SPEED SENSOR
REPEATTHE“INITIAL
START-UPPROCEDURE”.
REPLACETHEEC-12™
CONTROLLER
YES
AREANY LED'sILLUMINATED?
YES
ARE SAME RED LEDS ILLUMINATED ?
YES
CORRECT RESISTANCE?
NO
DISCONNECT CONNECTORATSPEEDSENSOR.INSPECT
THECONNECTOR,THENCHECKTHERESISTANCEBETWEEN
TWOPINSONSENSOR. RESISTANCEBETWEEN1500-2500
OHMSFORTHEBENDIX®WS-20™SPEEDSENSOR
YES
REPLACE THE SENSOR
NO
NO
GOTOSECTIONIII"INSPECTION
FORILLUMINATEDLED's"
NO
START HERE FROM
SECTION VI PART A GO TO SECTION III "INSPEC-
TION FOR ILLUMINATED LED's"
SAMELED'sILLUMINATED? NO
YES
RECONNECTCONNECTORATSPEED
SENSORANDEC-12™CONTROLLER.
PASSMAGNETOVER"RESET"ONEC-12™
CONTROLLER. REMOVEMAGNETAND
OBSERVELEDs
IGNITIONOFFSERVICEBRAKESNOTAPPLIED. REMOVE14
PINCONNECTORFROMEC-12™CONTROLLER. MEASURE
RESISTANCEBETWEENSPEEDSENSORPINSM&LANDN&PON
CONNECTOR.RESISTANCEFORBENDIX®WS-20™SPEED
SENSORISBETWEEN1500-2500OHMS. REFERTOVEHICLE
MANUALFORTHERESISTANCEVALUESIFOTHERTHAN
WS-20™SPEEDSENSORISINUSE.
REPAIRORREPLACESPEED
SENSORWIRINGHARNESS
ANDREPEATTHE“INITIAL
START-UPPROCEDURE”.
A B C D E FG H J K L M N P
M -SNS 2
L-SNS 2 N-SNS 1
P-SNS 1
TESTING SPEED SENSOR RESISTANCE
MAGNETHERE
RESETTING
EC-12™CONTROLLER
EC-12™CONTROLLERWIRE
HARNESSCONNECTOR

18
NOTES & REFERENCES
MC-12™
MODULATOR
CONTROLLER
ASSY.
TRAILER SERVICE AIR LINE
SPEED
SENSOR
EXCITER
RING
SPRING
BRAKE
VOLTLED (red) High/Low Voltage
MOD LED (red) M-12™Modulator Failure
SNS1 LED (red) Wheel Sensor Failure
SNS2 LED (red) Wheel Sensor Failure
CONT LED (red) EC-12™Controller Failure
PWR LED (green) EC-12™Controller Power
TRAILER
MOUNTED
STATUS LAMP
POWER FROM
STOPLIGHTS
GROUND
7PIN TRAILER ELECTRICAL
CONNECTOR
CONSTANT POWER FROM
TRACTOR IGNITION
(OPTIONAL CONNECTION)
GROUND
A
B
C
D
E
F
G
H
J
K
L
M
N
P
SENSOR 1
SNS 1
SENSOR 2
SNS 2
SENSOR 1
SNS 1
SENSOR 2
SNS 2
OPTIONAL
TRACTOR
MOUNTED STATUS
LIGHT
OPTIONAL
CONSTANT POWER
(TRACTOR IGNITION)
OPTIONAL
TRAILER
MOUNTED
STATUS LIGHT
STOPLIGHT SWITCH
POWER
14PINEC-12™CONTROLLER
CONNECTOR EC-12™CONTROLLER DIAGNOSTICWINDOW

19
NOTES & REFERENCES

BW1667 © 2004 Bendix Commercial Vehicle Systems LLC All rights reserved. 4/2004 Printed in U.S.A.