ELECTRONIC TROUBLESHOOTING 3176 DIESEL TRUCK ENGINE Caterpillar

3176 System Overview

The 3176 Diesel Truck Engine was designed from the beginning for electronic control. The injection pump, fuel lines and nozzles used in traditional Caterpillar Diesel Engines have been replaced with an electronic unit injector in each cylinder. A solenoid on each injector controls the amount of fuel delivered by the injector. An Electronic Control Module (ECM) sends a signal to each injector solenoid, to provide complete control of the engine.

Electronic Controls

The 3176 Diesel Truck Engine controller consists of two main components: the Electronic Control Module (ECM) and the Personality Module. The ECM is the computer and the personality module is the software for the computer (the personality module also stores the operating maps that define horsepower, torque curves, rpm, etc). The two work together (along with sensors to "see" and solenoid/injectors to "act") to control the engine. Neither one can do anything by itself.

The ECM determines a "desired rpm" based on the throttle signal, vehicle speed signal (only while in cruise), PTO switches (only while in cruise or PTO) and certain diagnostic codes. The ECM then maintains the desired engine rpm by sensing actual engine rpm and deciding how much fuel to inject in order to achieve the desired rpm.

Fuel Injection

The ECM controls the amount of fuel injected, by varying signals to the injectors. The injectors will inject fuel ONLY if the injector solenoid is energized. The ECM sends a 100 volt signal to the solenoid to energize it. By controlling the timing and duration of the 100 volt signal, the ECM can control injection timing and the amount of fuel injected.

The ECM sets certain limits on the amount of fuel that can be injected. "FRC Fuel Pos" is a limit based on boost pressure to control the fuel-air ratio, for emissions control purposes. When the ECM senses a higher boost pressure (more air into cylinder), it increases the "FRC Fuel Pos" limit (allows more fuel into cylinder). "Rated Fuel Pos" is a limit based on the horsepower rating of the engine. It is similar to the rack stops and torque spring on a mechanically-governed engine. It provides horsepower and torque curves for a specific engine family and rating. All of these limits are programmed by the factory into the Personality Module and are not programmable in the field.

Injection timing depends on engine rpm, load and other operation factors. The ECM knows where top-dead-center of cylinder number one is from the signal provided by the engine Speed/Timing Sensor. It decides when injection should occur relative to top-dead-center and provides the signal to the injector at the desired time.

Under certain conditions, the 3176 Engine may intentionally operate on just three cylinders. This feature is called "Three Cylinder Cutout" and occurs when the engine is operated under no load, at high rpm (when signals to the injectors are of very short duration). Under these conditions, the ECM does not inject fuel into cylinders 4, 5 and 6. This allows for more precise fuel metering to cylinders 1, 2 and 3. The accompanying change in feel and sound of the engine should not be diagnosed as an engine problem. When more power is needed, all six cylinders will be fueled and full power delivered.

Programmable Parameters

Certain parameters that affect 3176 Diesel Truck Engine operation may be changed through electronic service tools (either the ECAP or DDT). The parameters are stored in the ECM and passwords are used to prevent unauthorized changes.

Password protected parameters are either "System Configuration Parameters" or "Customer Specified Parameters". System Configuration Parameters are set at the factory and affect emissions or horsepower ratings within a family of engines. Factory passwords must be obtained and used to change System Configuration Parameters. Customer Specified Parameters are variable and can be used to affect such things as the cruise control, vehicle speed limits, progressive shifting, PTO operation and rpm/horsepower ratings within the limits set by the factory. Customer Passwords must be used to change Customer Specified Parameters.

If the driver has not had adequate training, some parameters may affect engine operation in ways that are not expected. This may lead to power or performance complaints, even though the engine is operating correctly.

For example, the Vehicle Speed Limit (VSL) parameter is programmable, to allow the customer to electronically limit vehicle speed. When the programmed limit is reached, the ECM reduces the amount of fuel injected into the cylinders. Engine power is controlled and the VSL will not be exceeded. Also, Progressive Shift Parameters (such as Low Gear limits and High Gear limits) will cause the ECM to pause at a programmed engine rpm. This pause can be helpful to encourage more fuel-efficient driving practices but may be misunderstood by the driver and result in a performance complaint.

Passwords

"System Configuration Parameters" are protected by factory passwords. System Configuration Parameters are those that affect horsepower family or emissions. Factory passwords are calculated on a computer system available only to Caterpillar dealers. Since factory passwords contain alphabetic characters, only the ECAP may change System Configuration Parameters.

"Customer Specified Parameters" are protected by customer passwords. Customer Specified Parameters are those that affect cruise control, vehicle speed limits, progressive shifting, horsepower rating within a family, and PTO operation. The customer passwords are programmed by the customer. Either the ECAP or DDT may normally change Customer Specified Parameters. However, if a customer uses alphabetic characters in his password, only the ECAP can be used to change those parameters.

The section on "Programming 3176 Parameters", in this manual, has more details on when passwords are needed and how to obtain them.

Self-Diagnostics

The 3176 Diesel Truck Engine has some ability to diagnose itself. When a problem is detected, a Diagnostic Code is generated and the Diagnostic Lamp is turned on. In most cases, the code is also stored in permanent memory in the ECM.

Diagnostic Codes that represent current faults are called ACTIVE. They indicate that a problem of some kind currently exists. They should always be serviced first. See the Troubleshooting Active Diagnostic Codes section in this manual for more details.

Diagnostic Codes stored in memory are called LOGGED. The problem may have been temporary or may have been repaired since the time it was LOGGED. Therefore, LOGGED diagnostic codes don't necessarily mean something needs to be repaired. LOGGED diagnostic codes may be helpful indicators for INTERMITTENT problems. In addition, some logged diagnostic codes record "events", rather than failures. See the section on Troubleshooting Logged Diagnostic Codes in this manual for more details.

3176 Engine System Component Diagram

NOTE: For Electrical Schematic, refer to Form No. SENR3912.

Location Of 3176 System Connectors

Location Of 3176 System Connectors

3176 Electronic Service Tools

The Caterpillar Service Tools for the 3176 Electronic Control System are designed to help the service technician analyze and locate faults or problems within the system. Their use is required to perform sensor calibrations and to read or change programmable engine parameters.

The tools have small plug-in modules, called Service Program Modules (SPM), to adapt the basic tools to a particular engine or application.

The 3176 Diesel Truck Engine requires either an Electronic Control Analyzer and Programmer (ECAP) or a Digital Diagnositc Tool (DDT) to communicate with the 3176 Electronic Control Module and read certain Diagnostic Codes. Both of these Service Tools are able to read the various sensor signals, as well as switch status (ON/OFF) inputs. Both the ECAP and DDT can measure Pulse Width Modulated (PWM) signals, such as those produced by the throttle position sensor (PWM Adapter required).

* It can program System Configuration Parameters (necessary to replace an ECM).

* It can perform functions requiring factory passwords which contain alphabetical characters.

* It has increased capacities and can display the status of up to 10 sensors or switches simultaneously.

* It can print parameters when used with the 8C9700 Rechargeable Portable Printer.

* It can be used with multiple Service Program Modules, at the same time.

* It can print gear "Split Charts" when equipped with the NEXG4512 Configuration Aid SPM and the 8C9700 Printer.

There are several adapter cables, Breakout 'T' cables, probes, etc., that are used with the various service tools. These allow the mechanic to gain access, for diagnosis, to wires carrying voltages and signals.

Either the heavy duty multimeter or the standard duty multimeter (listed in the chart) are suitable for making necessary voltage and resistance measurements on the 3176 System.

Other Special Tools include those needed to measure pressures and/or temperatures.

These tools, modules and adapters are listed in the chart along with their part numbers.

The following tools are recommended, but are not required.

8T8697 ECAP Service Tool
NEXG4507 Service Program Module (SPM)

7X6400 DDT Service Tool
NEXG4509 Service Program Module (SPM)

6V7800-or-6V7070 Digital Multimeter

8T8726 3-Pin Breakout 'T'; 8T8694 5-Pin Breakout 'T'; 9X0248 5-Pin Transducer Module Breakout 'T'; 8T8695 9-Pin Breakout 'T'; 7X1170 9-Pin Injection Breakout 'T'; 9X1160 40-Pin Breakout 'T'

3176 Wiring Schematic

The 3176 Wiring Schematic shown on the next page was the latest version available at the time this manual was published. It is the same as the 3176 Diesel Truck Engine Electrical Schematic, Form No. SENR3912 found in the Service Manual, 3176 Diesel Truck Engine, Form SENR3910. Electrical schematics are revised periodically. For the most current information, always check the revision number printed on the schematic and use the schematic with the latest revision.

Retain older harness wiring schematics on file, for use with the appropriate engine serial number production group.

Note A:

A dashed outline specifies a component required for optional features.

Note B:

No additional connections are allowed to any 3176 System wires. This includes all wires to sensors, switches, ground, battery (+), or battery (-).

Unless otherwise specified: All wire to be 18 AWG or larger. SAE J1128 type SXL or equivalent.

Note C:

Speedometer shown has internal signal (-) and ground connection. If not present, wire as shown in the following illustration.

Note D:

Ground connection is required for 7T6398 Vehicle Speed Buffer with the buffer supplying the signal to the speedometer.

Refer to P-213: Vehicle Speed Signal Test, for more information on grounding of Vehicle Speed Buffer and Speedometer.

Note E: (7T6398 Vehicle Speed Buffer):

Vehicle speed buffer is designed to operate with speedometers with the following signal characteristics:

Output voltage of the 7T6398 Vehicle Speed Buffer is a square wave with the same frequency as the magnetic pickup sensor signal. The amplitude will depend upon speedometer load current.

Note F: (3E0020 Vehicle Speed Buffer):

The output voltage of the 3E0020 Buffer for the speedometer, is a square wave (zero crossing) with the same frequency as the magnetic pickup sensor signal. The signal at P14, Pin E is a complement of the signal at P14, Pin C. Maximum signal amplitude at P14, Pin C and P14, Pin E is ± 10 volts DC. Amplitude will be ± 5 volts DC or greater if load current is less than 4 mA.

Note G:

The cylinder head ground stud must have a direct wire connection to battery (-). This connection can be made at the starter (-) terminal or main frame ground lug. This wire must handle full alternator charging current (6 AWG wire minimum).

Wiring Schematic For 12/24V Series Parallel Starting Systems