Ametek 387 User manual

Model 387
Instrument System
Service Manual
Document Number 072-40245
Rev. B

Every effort has been made to keep the information in this document current and ac-
curate as of the date of publication or revision. However, no guarantee is given or
implied that the document is error-free or that it is accurate with regard to any speci-
fication. AMETEK Dixson reserves the right to modify product designs and specifica-
tions without notice.
Free telephone assistance is available between 7 a.m. and 5:30 p.m. MST, Monday
through Thursday, or between 7:00 a.m. and 12:00 p.m. Fridays.
AMETEK Dixson Product Support Department
287 27 Road. Grand Junction, CO 81503
FAX: [phone]
Phone: [phone]
Toll-Free: [phone]
Revision Table
Revision Date Description
01/27/99 Initial release.
A 05/14/99 Changed all occurrences of “2100” to “387”, and of “self test” to
“initialization”; Fig. 5-22, corrected pin designations on J3 illus-
tration.
B 9/28/99 Added Chapter 6, “Using the Handheld Diagnostic Tool"; re-
moved all references to PTM/VTM replacement and to the ABS
system; improved Pyrometer troubleshooting instructions; up-
dated Warning Messages tables to reflect current configuration;
various other updates and changes resulting from Engineering
Dept. review.
ii 072-40245 B

Model 387 Instrument System Service Manual
072-40245 B iii
Table of Contents
1 Introduction 1-1
1.1 Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . 1-1
1.2 How To Use This Manual . . . . . . . . . . . . . . . . . . . . . . 1-1
1.3 System Components . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.4 What Makes the Model 387 Instrument System Different . . . . . . . . . . . . 1-2
2 Operation 2-1
2.1 Activating the Instrumentation . . . . . . . . . . . . . . . . . . . . 2-1
2.2 Select/Reset Switch . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3 Speedometer with Integral Message Center . . . . . . . . . . . . . . . . 2-1
2.4 Using the Speedometer Message Center . . . . . . . . . . . . . . . . . 2-2
2.4.1 Clock Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.4.2 Trip Odometer Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2.4.3 Clock Alarm Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2.5 Warning Alarms . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2.5.1 Red Warning LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2.5.2 Vehicle Safety Warning Messages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.5.3 System Fault Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
3 Functional Description 3-1
3.1 The Interface Module . . . . . . . . . . . . . . . . . . . . . . . 3-2
3.1.1 Pressure and Vacuum Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
3.1.2 Transducer Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
3.1.2.1 Pressure Transducer Module..................................................................................3-3
3.1.2.2 Vacuum Transducer Module (VTM)........................................................................3-4
3.1.3 Vacuum/Pressure and Pressure/Vacuum Transducer Modules . . . . . . . . . . . . . . . 3-4
3.2 J1708 Data Bus . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
3.3 Electronic Control Units . . . . . . . . . . . . . . . . . . . . . . 3-5
3.4 Speedometer with Integrated Message Center . . . . . . . . . . . . . . . 3-5
3.4.1 Select and Reset Switches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.4.2 Power Take-Off (PTO) Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.4.3 Two-Speed Axle Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.5 Diagnostic Capabilities . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.5.1 Power-On Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.5.2 Diagnostic Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3.6 Private Data Bus . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3.6.1 Five-Wire Cable Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3.6.2 Two-Inch Gauges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3.6.3 J1708 Data Bus and Private-Bus-Driven Gauges. . . . . . . . . . . . . . . . . . . . . . 3-8

iv 072-40245 B
3.6.4 Tachometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
3.6.4.1 Ammeter....................................................................................................................3-9
3.6.4.2 Voltmeter .................................................................................................................3-10
3.6.4.3 Pyrometer................................................................................................................3-11
3.6.4.4 Transmission and Axle Temperature Gauges ...........................................................3-12
3.6.4.5 Fuel Level.................................................................................................................3-13
3.7 Backlighting . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
4 Service Procedures 4-1
4.1 Some Important Dos and Donts . . . . . . . . . . . . . . . . . . . . 4-1
4.2 Replacing the Speedometer and Tachometer . . . . . . . . . . . . . . . . . 4-1
4.3 Servicing the Two-Inch Gauges . . . . . . . . . . . . . . . . . . . . . 4-2
4.3.1 Removal and Reinstallation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.3.2 Disassembling a Two-Inch Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
4.3.3 Reassembling a Two-Inch Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
4.4 Reprogramming a Two-Inch Gauge . . . . . . . . . . . . . . . . . . . . 4-5
4.5 Servicing the Interface Module . . . . . . . . . . . . . . . . . . . . . 4-5
4.5.1 Removing the Interface Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
4.5.2 Reinstalling the Interface Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
4.5.3 Reprogramming the Interface Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
4.6 Spare Parts Listing . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
5 Troubleshooting Procedures 5-1
5.1 Required Test Equipment . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.2 Troubleshooting Procedure Start Point . . . . . . . . . . . . . . . . . . . 5-2
5.2.1 The Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
5.3 Troubleshooting Procedures for Two-Inch Gauges . . . . . . . . . . . . . . . 5-4
5.3.1 Two-Inch Gauge Fails Initialization, No Pointer Movement, LED Never Lights. . . . . . . . . 5-5
5.3.2 Two-Inch Gauge Passes Initialization but LED Flashes . . . . . . . . . . . . . . . . . . . . 5-6
5.3.2.1 Air and Fuel Pressure Gauges....................................................................................5-7
5.3.2.2 Temperature Gauges..................................................................................................5-9
5.3.2.3 J1708 Data Bus Gauges ..........................................................................................5-11
5.3.2.4 Vacuum Gauges.......................................................................................................5-11
5.3.2.5 Voltmeter Gauge ......................................................................................................5-13
5.3.2.6 Ammeter Gauge.......................................................................................................5-14
5.3.2.7 Fuel Level Gauge......................................................................................................5-16
5.3.2.8 Pyrometer................................................................................................................5-17
5.4 Troubleshooting Procedures for the SMC. . . . . . . . . . . . . . . . . . 5-19
5.4.1 SMC Pointer Never Moves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20
5.4.2 Speedometer and Odometers Inaccurate . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21
5.4.3 Speedometer Accurate, Odometer Inaccurate . . . . . . . . . . . . . . . . . . . . . . . 5-21
5.4.4 Odometer Advances When PTO Engaged . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22
5.4.5 Speedometer Does Not Change Speed When Two-Speed Axle Engaged . . . . . . . . . . 5-23
5.4.6 Engine Hours Do Not Advance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

Model 387 Instrument System Service Manual
072-40245 B v
5.5 One or More Gauge Pointers Sweep . . . . . . . . . . . . . . . . . . 5-25
5.5.1 A J1708 Data Bus Gauge Pointer Sweeps . . . . . . . . . . . . . . . . . . . . . . . . 5-26
5.5.2 A Non-J1708 Data Bus Gauge Pointer Sweeps. . . . . . . . . . . . . . . . . . . . . . 5-26
5.5.3 Several (But Not All) Gauge Pointers Sweep . . . . . . . . . . . . . . . . . . . . . . . 5-27
5.5.4 SMC Pointer and All J1708 Data Bus Gauge Pointers Sweep . . . . . . . . . . . . . . 5-27
5.5.5 All J1708 Data Bus Gauge Pointers (Except the SMC Pointer) Sweep . . . . . . . . . . 5-29
5.5.6 All Gauge Pointers Except the SMC Pointer Sweep. . . . . . . . . . . . . . . . . . . . 5-30
5.5.7 Only the SMC Pointer Sweeps, and No Messages Appear . . . . . . . . . . . . . . . . 5-32
5.5.8 SMC Pointer Sweeps, and a NO DATA Message Appears . . . . . . . . . . . . . . . . 5-32
5.6 Warning Messages . . . . . . . . . . . . . . . . . . . . . . . 5-33
5.7 Backlighting Problems . . . . . . . . . . . . . . . . . . . . . . 5-34
5.7.1 Two-Inch Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-34
5.7.1.1 One Gauge Has No Backlighting...........................................................................5-34
5.7.1.2 More Than One Gauge Has No Backlighting.........................................................5-34
5.7.1.3 All Gauges Plus Tachometer Have No Backlighting..............................................5-35
5.7.2 SMC Has No Backlighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36
5.8 Select/Reset Switches not Working . . . . . . . . . . . . . . . . . . 5-36
5.9 Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . 5-38
6 Using the Handheld Diagnostic Tool 6-1
6.1 Care and Cleaning . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6.3 Reading Engine ECU Gauge Data . . . . . . . . . . . . . . . . . . . . 6-3
6.3.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
6.4 Reading Private Bus Gauge Data . . . . . . . . . . . . . . . . . . . . 6-6
6.4.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
6.5 Viewing Configuration Data . . . . . . . . . . . . . . . . . . . . . 6-8
6.5.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
6.6 Programming and Verifying Ports 5A and 5B . . . . . . . . . . . . . . . . 6-10
6.6.1 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
6.7 Programming the Main Transmission Temperature Warning LED. . . . . . . . . . 6-13
6.7.1 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
6.8 HDT Spare Parts . . . . . . . . . . . . . . . . . . . . . . . . 6-16

vi 072-40245 B
List of Illustrations
Figure 1-1 Panel and Interface Module..................................................................................................................1-2
Figure 2-1 System Initialization.............................................................................................................................2-1
Figure 2-2 Speedometer Message Center Displays..............................................................................................2-2
Figure 3-1 Instrumentation Block Diagram............................................................................................................3-1
Figure 3-2 387 System Interface Module..............................................................................................................3-2
Figure 3-3 Pressure Circuit....................................................................................................................................3-3
Figure 3-4 Pressure, Vacuum, and Pressure/Vacuum Transducer Modules...........................................................3-4
Figure 3-5 387 Speedometer with Message Center..............................................................................................3-5
Figure 3-6 System Initialization.............................................................................................................................3-6
Figure 3-7 J1708 Data Bus Gauges ......................................................................................................................3-8
Figure 3-8 Ammeter Circuit...................................................................................................................................3-9
Figure 3-9 Voltmeter Circuit ................................................................................................................................3-10
Figure 3-10 Pyrometer Circuit.............................................................................................................................3-11
Figure 3-11 Axle and Transmission Temperature Circuits ...................................................................................3-12
Figure 3-12 Fuel Level Circuit..............................................................................................................................3-13
Figure 4-1 Two-Inch Gauge Removal and Reinstallation........................................................................................4-2
Figure 4-2 Scaleplate Alignment...........................................................................................................................4-3
Figure 4-3 Two-Inch Gauge Disassembly..............................................................................................................4-4
Figure 4-4 Removing the Interface Module...........................................................................................................4-5
Figure 5-1 Gauge Initialization...............................................................................................................................5-3
Figure 5-2 Checking Two-Inch Gauge Power.........................................................................................................5-5
Figure 5-3 Checking Pressure Gauges with Standard Test Gauge.........................................................................5-7
Figure 5-4 Checking Temperature Sensor Wiring................................................................................................5-10
Figure 5-5 Testing the Air and Fuel Restriction Gauges.......................................................................................5-12
Figure 5-6 Testing the Voltmeter Gauge ..............................................................................................................5-13
Figure 5-7 Testing the Ammeter Gauge...............................................................................................................5-15
Figure 5-8 Testing the Fuel Level Gauges............................................................................................................5-16
Figure 5-9 Testing the Pyrometer........................................................................................................................5-17
Figure 5-10 Testing the Pyrometer (continued)...................................................................................................5-18
Figure 5-11 Troubleshooting SMC Power and Ground.........................................................................................5-20
Figure 5-12 Troubleshooting the PTO (Power Take-Off) Input..............................................................................5-22
Figure 5-13 Troubleshooting the Two-Speed Axle Input......................................................................................5-23
Figure 5-14 SMC Pointer and All J1708 Data Bus Gauge Pointers Sweep..........................................................5-28
Figure 5-15 All J1708 Data Bus Gauge Pointers (except SMC) Sweep...............................................................5-29
Figure 5-16 Checking J1708 Data Bus Wire Continuity......................................................................................5-31
Figure 5-17 Checking Private Bus Wire Continuity .............................................................................................5-31
Figure 5-18 Gauge Backlighting Problem (except SMC) .....................................................................................5-35
Figure 5-19 SMC Backlighting Problem ..............................................................................................................5-36
Figure 5-20 Troubleshooting the Select and Reset Switches ..............................................................................5-37

Model 387 Instrument System Service Manual
072-40245 B vii
List of Tables
Table 2-1 Red Warning LEDs.................................................................................................................................2-5
Table 2-2 Vehicle Safety Warning Messages ........................................................................................................2-6
Table 4-1 387 System Spare Parts........................................................................................................................4-6
Table 5-1 Troubleshooting Starting Point...............................................................................................................5-2
Table 5-2 Two-Inch Gauge Problems.....................................................................................................................5-4
Table 5-3 Problems Indicated by Flashing Gauge LEDs.........................................................................................5-6
Table 5-4 SMC Problems.....................................................................................................................................5-19
Table 5-5 Problems Indicated by Sweeping Pointer(s) ........................................................................................5-25
Table 5-6 Warning Messages..............................................................................................................................5-33
Table 5-7 System Fault Messages ......................................................................................................................5-33
Table 6-1 HDT Spare Parts ..................................................................................................................................6-16
Figure 5-21 Instrumentation Harness Layout......................................................................................................5-38
Figure 5-22 Gauge Connector Wiring..................................................................................................................5-39
Figure 5-23 Instrumentation Connector Pinout Diagram .....................................................................................5-40
Figure 6-1 Hand-held Diagnostic Tool....................................................................................................................6-2
Figure 6-2 Connecting the HDT to the Diagnostic Connector................................................................................6-3
Figure 6-3 Connecting the HDT to the Private Bus ................................................................................................6-6

Notes:
viii 072-40245 B

1 Introduction
1.1 Purpose and Scope
The purpose of this manual is to provide Peterbilt with the knowledge required to
produce their own repair procedures. This manual contains the technical repair informa-
tion necessary to diagnose and repair the Model 387 Instrument System (also referred
to as simply the “instrumentation”). The information in this manual is not propri-
etary and can be used as Peterbilt sees fit.
The manual describes how to operate, service, and troubleshoot the instrumentation
installed in vehicles that broadcast engine- and speed-related information over a
public data bus (the SAE J1708 data bus). For information about the vehicle’s Electronic
Control Unit(s), wiring diagrams, the SAE J1708 data bus, external sensors and other
components that are not part of the instrumentation, please refer to the appropriate
vehicle service documentation.
1.2 How To Use This Manual
The manual is divided into six chapters:
•Introduction - Contains a brief introduction to the product and to the
manual itself.
•Operation - A complete operator’s manual. Written for the vehicle opera-
tor, this chapter describes how to use the instrumentation and how to in-
terpret the information it presents. If you are going to operate the vehicle,
you should read and understand the information in this chapter.
•Functional Description - Describes the components that make up the in-
strumentation and how they communicate with other systems in the vehi-
cle. An understanding of the information in this chapter will help you
diagnose and find problems in the instrumentation. If you are going to ser-
vice the instrumentation, you should read and understand the information
in this chapter.
•Service - Describes how to remove, disassemble, and reinstall the compo-
nents of the instrumentation. It contains a spare parts list, and other im-
portant information. Do not service the instrumentation until you have
read and understand the information in this chapter.
•Troubleshooting - Provides detailed troubleshooting information that will
help you identify faulty components within the instrumentation.
•Using the Handheld Diagnostic Tool (HDT) - Describes the operation of
the handheld diagnostic tool used to help diagnose problems with the
instrumentation.
Model 387 Instrument System Service Manual
072-40245 B 1-1 Introduction

1.3 System Components
The instrumentation consists of a 338-inch speedometer with an integrated message
center, a 338-inch tachometer, several 2-inch gauges, a Select/Reset switch, and a
remotely mounted Interface Module. Figure 1-1 shows how a typical system with
four 2-inch gauges might look, along with an Interface Module.
1.4 What Makes the Model 387 Instrument System Different
In conventional instrumentation, each electrical gauge is connected to a sensor by a
signal wire and a return wire. Additional wires for illumination, power, ground and
warning lights could total as many as six wires per gauge. Thus, a panel with 10
gauges plus a speedometer and a tachometer could require up to 60 separate wires.
By comparison, the Model 387 Instrument System uses a single 5-wire cable to con-
nect all the gauges together. This significantly reduces the number of wires behind
the instrument panel and makes the system much easier to troubleshoot and service.
The instrumentation is easy to repair. The 2-inch gauges can be disconnected, remov-
ed from the panel, disassembled, reassembled, and reinstalled without tools, and
they are maintenance-free.
With the exception of the scaleplate, all 2-inch gauges are identical. Each scaleplate is
coded and when installed in the gauge, configures the gauge to the function shown
on the scaleplate. This reduces the spare parts inventory by requiring only a few
blank gauges and a supply of inexpensive scaleplates rather than a complete spare
gauge of each type.
The instrumentation can also display warning messages and audible alarms, and has
built-in diagnostic capabilities to help diagnose problems.
Introduction 1-2 072-40245 B
Figure 1-1 Panel and Interface Module

2 Operation
2.1 Activating the Instrumentation
Turning on the ignition activates the instrumentation and starts the initialization de-
scribed in Figure 2-1.
Service the vehicle if any of the following conditions occur after the initialization:
•The speedometer or tachometer pointer sweeps back and forth in a wind-
shield wiper motion.
•A 2-inch gauge’s pointer sweeps back and forth in a windshield wiper mo-
tion and stops at a 10:00 position with its red LED on.
•A 2-inch gauge’s pointer stays at a 7:00 position and its red LED flashes.
•A 2-inch gauge’s pointer goes to and remains at a 12:00 position with its
red LED on.
2.2 Select/Reset Switch
A Select/Reset switch on the dash allows you to select, set, and reset message center
displays. It also allows you to scroll through active system warning messages.
2.3 Speedometer with Integral Message Center
The speedometer and its message center together are called the SMC. The SMC nor-
mally displays road speed and the odometer reading. The SMC can also display
other functions as shown in Figure 2-2.
Model 387 Instrument System Service Manual
072-40245 B 2-1 Operation
Figure 2-1 System Initialization

To view a different function, press and release the Select switch until the desired
function appears.
The message center goes into a “sleep” mode (i.e. goes blank) when the ignition is
turned off. Each time you press the Select switch, the message center is “awakened”
for 10 seconds. This allows you to scroll through the different functions.
If a warning alarm is triggered, a warning message will override all other displays
until the condition that caused the warning alarm is corrected. Some warning alarms
include an audible warning. Warning alarms are described in detail in Section 2.5.
2.4 Using the Speedometer Message Center
2.4.1 Clock Operation
To display the clock time, press and release the Select switch until the clock is dis-
played.
To change the clock time -
1. Press and release the Reset switch. The Hours display will flash, indicating the
value can be changed.
2. Press the Select switch to change the Hours value, or press the Reset switch to ac-
cept the displayed value and enable the Minutes value to be changed. To change
from AM to PM, scroll through 12 hours.
3. When the Minutes value is flashing, press the Select switch to change the value,
or press the Reset switch to accept the displayed value and exit the Change Time
function. Scrolling the Minutes value past 59 will not change the Hours value.
Operation 2-2 072-40245 B
Figure 2-2 Speedometer Message Center Displays

2.4.2 Trip Odometer Operation
To display the Trip 1 or 2 Odometer, press and release the Select switch until
XXXXT1 or XXXXT2 is displayed (XXXX = the actual mileage reading).
To reset a trip odometer to zero -
1. Display the odometer to be reset (Trip 1 or Trip 2)
2. Press and hold the Reset switch for 3 seconds.
2.4.3 Clock Alarm Operations
To display the alarm time, press and release the Select switch until an AL appears
along with a time value.
To change the alarm time -
1. Press and release the Reset switch. The Hours digits will begin to flash, indicat-
ing the values can be changed.
2. Press the Select switch to change the Hours value, or press the Reset switch to ac-
cept the displayed value and enable the Minutes value to be changed. To change
from AM to PM, scroll through 12 hours.
3. When the Minutes value is flashing, press the Select switch to change the value.
Scrolling the Minutes value past 59 will not change the Hours value.
4. Press the Reset switch to accept the displayed value and exit the Change Alarm
Time function. This also activates the alarm and an asterisk(*)will appear in the
first digit of the Clock display to indicate the alarm is on.
To activate or deactivate the alarm tone, from any display, press and hold the Select
switch longer than three seconds.
To silence the alarm tone while it is sounding, press and release the Select switch
while the alarm is sounding.
2.5 Warning Alarms
A warning alarm indicates that some condition in the vehicle requires attention. A
warning alarm can be indicated in the following ways:
•Red warning LEDs in the 2-inch gauges
•Vehicle safety warning messages in the SMC
•System fault warning messages in the SMC
A warning alarm will continue until the condition that caused it is corrected. At that
time, the SMC will display a Reset message for 10 seconds, and the warning indica-
tions will cease. Pressing the Reset switch clears the Reset message sooner.
2.5.1 Red Warning LEDs
Table 2-1 on page 2-5 lists the conditions which light the red warning LEDs. Some of
the LEDs light when the Interface Module receives the appropriate message over the
Model 387 Instrument System Service Manual
072-40245 B 2-3 Operation

J1708 data bus. Other LEDs light as determined by Interface Module programming,
and some warning LEDs are not used. Column 3 lists the condition that causes the
warning LED to light.
You cannot dismiss or override red warning LED indications. A red warning LED
will remain on until the condition causing it is corrected.
Note - Not all gauges listed are currently available.
2.5.2 Vehicle Safety Warning Messages
Messages advising of unsafe operating conditions can appear in the SMC. Examples
are a major engine or transmission problem (low oil pressure, high temperature, low
coolant level) and a problem with the brake safety (low air pressure). An audible
alarm will accompany these warning messages.
Vehicle safety warning messages are listed in Table 2-2 on page 2-6. Column 1 shows
the warning message as it appears in the SMC, and column 2 identifies its meaning.
Column 3 identifies the gauge whose red warning LED lights. Column 4 shows the
associated Reset message.
You can temporarily override vehicle safety warning messages two ways:
1. Press the Reset switch for 3 seconds. This will dismiss the message and silence
the buzzer. If an active alarm still exists, the message and buzzer will return.
2. Press the Reset switch for 1 second, then press the Select switch to display any
other function. The warning message will disappear for 60 seconds. It will then
reappear and remain until the condition causing it is corrected. The audible
alarm will continue to sound.
2.5.3 System Fault Messages
A system fault message indicates a problem exists with the Model 387 Instrument
System that does not directly affect vehicle safety. These occur when the ignition is
first switched on. The messages are:
IM CAL, IM CFG, IM DIAG, IM LIN, IM SLFT, ODO ERR, NO DATA, SMC MEM.
System fault messages are detected by the Interface Module or the SMC. No gauge
LED is associated with them, no audible warning will sound, and no Reset message
will appear.
The NO DATA message can occur any time, not just during System Initialization.
Operation 2-4 072-40245 B

Model 387 Instrument System Service Manual
072-40245 B 2-5 Operation
Gauge Indication When Led Is On Activating Condition
Air Cleaner Restriction Clogged More than 25" of water (H2O)
Air Tank 1 Too low Less than 66 psi
Air Tank 2 Too low Less than 66 psi
Air Starter Air Pressure No indication Not activated
Ammeter Incorrect discharge rate >25 amps when RPM <1200, or
>2 amps when RPM >1200
Auxiliary Transmission Oil Temp Too high Higher than 230° F
Brake Saver Application Air Pressure No indication Not activated
Brake Saver Oil Temp Too high Higher than 230° F
Center Drive Axle Oil Temp Too high Higher than 230° F
Engine Load No indication Not activated
Engine Oil Pressure Too low Engine ECU
Engine Oil Temperature Too high Engine ECU
Front Drive Axle Oil Temp Too high Higher than 230° F
Fuel Filter Restriction Clogged More than 7" of mercury
Fuel Level (left, right, or main tank) Low fuel 18tank or less
Fuel Pressure No indication Not activated
Load Gauge Air Pressure No indication Not activated
Main Transmission Oil Temp Too high Programmable
Manifold Boost No indication Not activated
Pusher Suspension Air Pressure No indication Not activated
Pyrometer Too high Higher than 1200°F
Tractor Brake Applic. Air Pressure No indication Not activated
Rear Drive Axle Oil Temp Too high Higher than 230° F
Tag Suspension Air Pressure No indication Not activated
Trailer Brake Applic. Air Pressure No indication Not activated
Voltmeter Too low or too high >15 volts or <10 volts
Engine Coolant Temp Too high Engine ECU
6X6 Front Drive Axle Oil Temp Too high Higher than 230° F
Air Deflector Position No indication Not activated
Transfer Case Oil Temp Too high Higher than 230° F
Table 2-1 Red Warning LEDs

Operation 2-6 072-40245 B
Warning
Message Condition Associated Gauge LED Reset Message
H2O TMP Coolant temperature high Water Temperature H2OT OK
LOW AIR1 Air tank #1 pressure low Primary Air Pressure AIR1 OK
LOW AIR2 Air tank #2 pressure low Secondary Air Pressure AIR2 OK
OILPRES Engine oil pressure low Engine Oil Pressure OIL OK
OIL TEMP Engine oil temperature high Engine Oil Temperature OILT OK
TRANTMP Main transmission oil
temperature high Main Transmission Oil Tem- perature TRAN OK
CAUTION! If a message that is not listed in this table appears, do not ignore it. The vehicle
should be serviced regardless of the message that appears.
Table 2-2 Vehicle Safety Warning Messages

3 Functional Description
This section describes the instrumentation on a functional level. It is not necessary to
read this section to troubleshoot and service the system. It is intended to provide a
more detailed understanding of how the system works. Figure 3-1 illustrates the ma-
jor components and signal flow.
Note - Throughout this manual, the terms “public data bus” or “public bus” refer
specifically to the J1708 data bus.
Caution! Never store gauges face down. The gauge meter movements use an oil damping sus-
pension. If a gauge is left face-down longer than 15 minutes, the oil may begin to
run out. This causes inaccurate gauge readings, premature gauge failure, and
voids the warranty.
Model 387 Instrument System Service Manual
072-40245 B 3-1 Functional Description
Figure 3-1 Instrumentation Block Diagram

3.1 The Interface Module
The Interface Module controls the instrumentation by collecting information from
various sources and converting that information into gauge pointer information
which it then sends to the gauges. It is an environmentally sealed unit and it is usu-
ally mounted beneath the cab and against the frame rail. It is connected to the J1708
data bus, and to switches, sensors and pressure/vacuum hoses throughout the vehicle.
All gauge and display information is gathered by the Interface Module except:
•Road Speed and Engine Hours - Road Speed and Engine Hours messages
are sent directly to the SMC over the J1708 data bus. The SMC also uses
road speed messages to compute mileage and display it on the odometers.
•Select and Reset Input - These switched inputs are applied directly to the
SMC.
•Clocks - Clock and Alarm Clock information is generated within the SMC.
•Gauge Backlighting - Power for the gauge backlighting comes from an ex-
ternal dimming control and completely bypasses the Interface Module.
3.1.1 Pressure and Vacuum Inputs
Hose connections to the transducer modules provide pressure or vacuum to the In-
terface Module. The Interface Module converts the pressure and vacuum signals to
data and places that data on the private data bus to drive the pressure gauges. Con-
nections are shown in Figure 3-3.
If an Air Filter Restriction gauge is present, its input must be connected to port 5A. If
a Fuel Filter Restriction gauge is present, its input must be connected to port 5B.
Functional Description 3-2 072-40245 B
Figure 3-2 387 System Interface Module

Other pressure inputs are connected to port 5A or 5B, whichever is available depend-
ing upon whether an Air Filter or a Fuel Filter Restriction gauge is present.
Whenever the Interface Module is replaced, you must reprogram it recognize the
pressure gauges. You do not need to reprogram it when replacing defective gauges.
3.1.2 Transducer Modules
Four different transducer modules are available. All modules consist of pressure or
vacuum transducers (or both) mounted in a common thermoplastic base inside a
metal housing. Each transducer converts pressure (or vacuum) into a DC voltage that
can be used by the Interface Module.
Transducer modules cannot be replaced in the field.
3.1.2.1 Pressure Transducer Module
A pressure transducer module (PTM) contains two identical pressure transducers,
each capable of handling up to 150 psi. It can be connected to air, fuel, or oil pressure
inputs. It is mounted at port 1A/1B and connected to Air Tank 1 and Air Tank 2 air
pressure. A second PTM may also be mounted at port 5A/5B and connect to addi-
tional pressure sources. See Figure 3-4 on page 3-4.
Model 387 Instrument System Service Manual
072-40245 B 3-3 Functional Description
Figure 3-3 Pressure Circuit

3.1.2.2 Vacuum Transducer Module (VTM)
A vacuum transducer module (VTM) contains two vacuum transducers. The VTM is
used for the Air Filter Restriction and Fuel Filter Restriction gauges. The VTM must
be mounted at port 5A/5B only.
The vacuum transducers are not identical. The Air Filter Restriction end must go to
port 5A, and the Fuel Filter Restriction end must go to port 5B as shown in Figure 3-
4.
3.1.3 Vacuum/Pressure and Pressure/Vacuum Transducer Modules
Two types of combination modules are available. One type contains a pressure trans-
ducer and an Air Restriction transducer; the other type contains a pressure trans-
ducer and a Fuel Filter Restriction transducer. Combination modules are not
interchangeable and are mounted at port 5A/5B. If used, the Air Filter Restriction
end must go to port 5A, and the Fuel Filter Restriction end must go to port 5B as
shown in Figure 3-4.
CAUTION - The sudden application of pressure to transducer modules can destroy them and
void their warranties. Always apply pressure gradually and at a rate that does not
exceed 150 PSI per second.
3.2 J1708 Data Bus
The J1708 data bus is a public data bus consisting of a pair of twisted-wires. It allows
electronic devices and other equipment in the vehicle to send and receive data. The
two wires making up the J1708 data bus are part of the vehicle’s wiring harness. Be-
cause it connects to many different components in widely separated locations, a
problem with the data bus or with one of the component’s connected to it can some-
times be hard to isolate. For a complete description of the J1708 data bus and data
Functional Description 3-4 072-40245 B
Figure 3-4 Pressure, Vacuum, and Pressure/Vacuum Transducer Modules