General Information

The Powertrain Control Module (PCM) has been programmed to monitor many different circuits for diesel powered vehicles. If a problem is sensed in a monitored circuit often enough to indicate an actual problem, a diagnostic trouble code (DTC) is stored. The DTC will be stored in the PCM memory for eventual display to the service technician. If the problem is repaired or ceases to exist, the PCM cancels the DTC after 51 engine starts.

Certain criteria must be met for a DTC to be entered into PCM memory The criteria may be a specific range of engine RPM, engine temperature and/or input voltage to the PCM.

It is possible that a DTC for a monitored circuit may not be entered into memory even though a malfunction has occurred. This may happen because one of the DTC criteria for the circuit has not been met.

A DTC indicates that the PCM has recognized an abnormal signal in a circuit or the system. A DTC may indicate the result of a failure, but never identify the failed component directly.

There are several operating conditions that the PCM does not monitor and set a DTC for. Refer to Monitored Circuits and Non-Monitored Circuits.