Usage:
The Diagnostic Process
System Operation
The 3176 Diesel Truck Engine was designed from the beginning for electronic control. The injection pump, fuel lines and nozzles used in traditional Caterpillar 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 electronic system consists of two main components: the Electronic Control Module (ECM) and the Personality Module. The ECM is the computer which controls the 3176 engine. The Personality Module is the software which controls how the computer behaves (the personality module stores the operating maps that define horsepower, torque curves, rpm, etc.). The two must be used together: neither can do anything by itself.
The ECM determines a "desired rpm" based on the throttle signal, vehicle speed signal (only while in cruise control), PTO switches (only while in 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 specific engine family and rating. All of these limits are programmed at 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 on 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. The accompanying change in sound and feel of the engine should not be mis-diagnosed as an engine problem. When more power is needed, all six cylinders will be fueled and full power delivered.
Caterpillar Engine Protection
For 7LG7500 and later engines, Caterpillar provides a factory installed Engine Protection system. The Caterpillar Engine Protection system monitors engine oil pressure, coolant temperature, and coolant level. The oil pressure and coolant temperature sensors are standard on all 1992 and newer engines. The Vehicle OEM is responsible for providing the coolant level sensor and the associated harness. The coolant level sensor is the only individually selectable component of Caterpillar Engine Protection. It is ENABLED or DISABLED through a Customer Programmable Parameter.
Caterpillar Engine Protection can be programmed to four different modes; OFF, WARNING, DERATE, and SHUTDOWN, with the additional option of enabling or disabling the Coolant Level Sensor. Note that all sensors will operate in the Engine Protection Mode selected. For example, if DERATE mode were selected the engine will derate if the Coolant Temperature, Oil Pressure, or Coolant Level (if enabled) Sensors flag the necessary condition. The Coolant Level Sensor can not be selected for WARNING, Oil Pressure and Coolant Temperature for DERATE.
If Caterpillar Engine Protection is programmed to OFF, the control system disables those diagnostics associated with Caterpillar Engine Protection: Low Oil Pressure, Very Low Oil Pressure, Oil Pressure Sensor Open/Short Circuit, High Coolant Temperature, Very High Coolant Temperature, Low Coolant Level, Very Low Coolant Level, and Coolant Level Sensor Fault. The engine will still use the Coolant Temperature Sensor signal for Cold Mode operation, and the diagnostics available for flagging incorrect sensor operation (Coolant Temp Sensor Open/Short Circuit). The Oil Pressure Sensor signal will be ignored. Because the Oil Pressure Sensor and Coolant Level Sensor (when installed) harness are still present on the engine, the harness could cause a problem in the event it had a short circuit in the supply wire to ground. Therefore, these items should not be excluded from diagnostic procedures.
When Caterpillar Engine Protection is programmed to WARNING, the control system will only warn the operator of a potential problem by turning on the Warning Lamp solid (continuously on), the Diagnostic Lamp (indicating the presence of an Active diagnostic code), and logging the appropriate diagnostic. The engine will take no further action. For the DERATE mode, the system will first warn the operator with the solid operation of the Warning Lamp as for WARNING mode, but, if conditions persist, the control system will go to DERATE mode. During DERATE mode the Warning Lamp will begin to flash, and the available engine power and vehicle speed will be limited. Power will continue to be limited as long as the conditions causing the problem exist. The SHUTDOWN mode causes the system to first go through the DERATE mode just described. If conditions persist the engine will shutdown 30 seconds after the DERATE mode has been entered.
Programmable Parameters
Certain parameters that affect 3176 Diesel Truck Engine operation may be changed with electronic service tools (either the ECAP or DDT). The parameters are stored in the ECM, and are protected from unauthorized changes by passwords.
These parameters are either "System Configuration Parameters" or "Customer Parameters". System Configuration Parameters are set at the factory and effect emissions or horsepower ratings within a family of engines. Factory passwords must be obtained and used to change System Configuration Parameters. Customer Parameters are variable and can be used to affect cruise control, vehicle speed limits, progressive shifting, rpm/horsepower ratings within the limits set by the factory, Caterpillar Engine Protection, and PTO operation. Customer Passwords are necessary to change Customer Specified Parameters.
Some parameters may affect engine operation in ways a driver does not expect without adequate training. These may lead to power or performance complaints, even when the engine is performing to specifications.
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. 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. System Configuration Parameters affect horsepower family or emissions.
"Customer Parameters" are protected by customer passwords. The customer passwords are programmed by the customer. Either the ECAP or DDT may change customer Parameters (although if a customer programs his password with alphabetic characters using an ECAP, only an ECAP can change Customer Parameters, since the DDT does not have alphabetic characters). See section 2.0 on "Programming 3176 Parameters", for more details when passwords are needed and how to obtain them.
Self-Diagnostics
The 3176 electronics have some ability to diagnose themselves. 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.
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 section on "Troubleshooting Diagnostic Codes" in this manual for more details.
Codes stored in memory are called LOGGED. Since the problem may have been temporary or may have been repaired since the time it was logged, logged codes don't necessarily mean something needs to be repaired. They are instead meant to be an indicator of probable causes for intermittent problems. In addition, some logged codes record "events", rather than failures. Codes not requiring passwords to clear are automatically deleted after 100 ECM hours. See the section on "Troubleshooting Diagnostic Codes" in this manual for more details.
3176 EUI Electronic System
7LG1-7499 - 3176 System Component Diagram
7LG7500-UP - 3176 System Component Diagram
Electrical Connectors and Functions
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 in order to perform sensor calibrations electronically, and to read or change engine parameters. The basic tools have small plug-in modules, called Service Program Modules (SPM), to adapt the basic tools to the specific Caterpillar electronic engine application.
The two principle tools are the Electronic Control Analyzer Programmer (ECAP), and the Digital Diagnostic Tool (DDT). Both are able to Communicate with the 3176 Electronic Control Module to read Diagnostic Codes, to read the various sensor output signals such as engine rpm, or boost pressure, and are capable of electronically calibrating the 3176 sensors.
Both the ECAP (requires PWM adapter to measure at the sensor) and DDT can measure Pulse Width Modulated (PWM) signals, such as those produced by the Throttle Position Sensor. The ECAP (only) is required when entering Factory Passwords, or for customer passwords containing alpha characters.
There are several adapter cables, breakout "T" cables, probes, etc., that are used with the service tools in order to gain access for measurements of wires carrying voltages and signals. Both heavy duty multimeter and the standard duty multimeter (listed below) are suitable for making the necessary measurements. Other Special Tools include those needed to measure pressure or temperature.
1Refer to Special Instruction Form No. SEHS8742: Using the 8T8697 Electronic Control Analyzer Programmer (ECAP).
2The NEXG4522 Dual SPM will service all 3406 PEEC and 3176 truck engines. The NEXG4522 is a subscription, since it is anticipated that it will be changing at regular intervals.
3Refer to Special Instruction Form SEHS8807: Installation and Use of the 8C9801 Pulse Width Modulated (PWM) Signal Adapter Group.
4Refer to Special Instructio nForm No. SEHS8740 for using the 8C9700 Rechargeable Portable Printer.
5Refer to Special Instruction Form No. SEHS9076: Using the 7X6400 digital Diagnostic Tool (DDT) Group.
6Refer to Special Instruction Form No. SEHS8868.
7Refer to Operating Manual Form No. SEHS8834 for using the NEXG4512 Customer Parameter Configuration Aid Service Program Module.
8Refer to Special Instruction Form No. SEHS8833 for installing the 7X1180 Internal Expansion Board in the 8T8697 ECAP Service Tool.
9Refer to Operating Manual Form No. SEHS9349 for using the NEXG4522 Truck Functions Dual Service Program Module.
10Refer to Operating Manual Form No. SEHS8743 for using the NEXG4509 3176 Service Program Module.
11Refer to Special Instructin Form No. SEHS8907 for using the 1U5470 Engine Pressure Group.
3176 Sensor and Connector Locations
7LG7500-UP - 3176 Wiring Diagram
7LG1-7499 - 3176 Wiring Diagram
