Refer to Systems Operation, "Electronic Control System Components" for diagnostic codes and for diagnostic code information. For an explanation of each diagnostic code, refer to Troubleshooting.
Diagnostic codes are used by the engine system to warn the vehicle operator of a problem. Also, diagnostic codes are used by the engine system to indicate the nature of a problem to the service technician. Some codes are used only to record an event. These codes do not indicate problems that need repair.
An "ACTIVE" diagnostic code represents a problem that should be investigated and corrected as soon as possible. Repairing the cause of an "ACTIVE" code will cause the code to be cleared.
When an "ACTIVE" code is generated, the diagnostic lamp will turn on and the diagnostic lamp will remain turned on. While the diagnostic lamp is turned on, the diagnostic lamp will blink at five second intervals. If the condition that generates the fault occurs for only a brief moment, the lamp will turn off after five seconds. In this situation, the code will be logged.
Logged Diagnostic Codes And Events
When the ECM generates a diagnostic code, the code will be active and the code may be logged in permanent memory within the ECM. The ECM has an internal diagnostic clock and the ECM will record the time for the fault logging. Knowing the time and frequency of the code can be a valuable indication when a technician is troubleshooting intermittent problems. Logged codes can be downloaded or erased with an electronic service tool. These logged codes can also be a valuable indication when a technician is troubleshooting intermittent problems.
Diagnostic Codes that are logged repeatedly may indicate a problem that needs special investigation. Some codes may not need attention until a scheduled maintenance interval. If only both of the following conditions occur, the code may not need any attention until a scheduled maintenance interval:
- the logged code has occurred a few times.
- the code does not result in concerns from the operator.
Certain fault codes and/or event codes cause the system to make major changes in the following parameters:
- engine operation
- limits of engine operation
These changes result from the generation of the code.
Note: The most likely cause of an intermittent problem is a faulty connection or damaged wiring. The next most likely cause of an intermittent problem is a component failure. A sensor or a switch are typical examples of components that could fail. The least likely cause of an intermittent problem is the ECM.
The Caterpillar electronic service tools for the electronic control systems are designed to help the service technician analyze diagnostic codes and problems within the system. Also, the Caterpillar electronic service tools for the electronic control systems are designed to help the service technician locate diagnostic codes and problems within the system. The electronic service tool is required to perform sensor calibrations and the electronic service tool is required in order to monitor programmable parameters of the engine. Also, the electronic service tool is required in order to change programmable parameters of the engine. For a list of service tools and procedures, refer to Troubleshooting.
Accelerator Pedal (Throttle) Position Sensor
The accelerator pedal position sensor converts the mechanical accelerator pedal position into an electrical signal. This electrical signal is sent to the ECM. Sensor output is a constant frequency signal with a pulse width that varies with the accelerator pedal position. This output signal is called a "Duty Cycle" or a "Pulse Width Modulation" signal. This output signal is expressed as a percentage between 0 percent and 100 percent.
The accelerator pedal position sensor is attached directly to the accelerator pedal and the accelerator pedal position sensor requires no adjustment. The sensor will produce a "Duty Cycle" between 10 percent and 22 percent at the low idle. When the engine is running at low idle, the accelerator pedal is released. The sensor will produce a "Duty Cycle" between 75 percent and 90 percent at high idle. When the engine is running at high idle, the accelerator pedal is fully depressed. The percent of duty cycle is translated in the ECM into an accelerator pedal position between 3 percent and 100 percent.
An incorrectly calibrated pedal mounted sensor assembly can not be adjusted. An incorrectly calibrated pedal mounted sensor assembly must be replaced.