Description of On-Board Diagnostics

GENERAL INFORMATION
The Powertrain Control Module (PCM) monitors critical input and output circuits of the charging system, making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the OBD system. Some circuits are checked continuously and some are checked only under certain conditions.

If the OBD system senses that a monitored circuit is bad, it will put a DTC into electronic memory The DTC will stay in electronic memory as long as the circuit continues to be bad. The PCM is programmed to clear the memory after 50 engine starts if the problem does not occur again.

DIAGNOSIS TROUBLE CODES

Generator Diagnostic Trouble Code:

Diagnostic Trouble Codes (DTC) are two-digit numbers flashed on the malfunction indicator (Check Engine) lamp that identify which circuit is bad. Refer to On Board Diagnostic for more information. A DTC description can also be read using the DRB scan tool. Refer to the appropriate Powertrain Diagnostic Procedures for information.

A DTC does not identify which component in a circuit is bad. Thus, a DTC should be treated as a symptom, not as the cause for the problem. In some cases, because of the design of the diagnostic test procedure, a DTC can be the reason for another DTC to be set. Therefore, it is important that the test procedures be followed in sequence, to understand what caused a DTC to be set.

See Starting and Charging/Charging system/Alternator/Generator Diagnostic Trouble Code chart for DTC's which apply to the charging system. Refer to the Powertrain Management/computers and Control System/Diagnostic Procedures to diagnose an on-board diagnostic system trouble code.

Retrieving Diagnostic Trouble Codes
To start this function, cycle the ignition switch ON-OFF-ON-OFF-ON within 5 seconds. This will cause any DTC stored in the PCM memory to be displayed. The malfunction indicator (Check Engine) lamp will display a DTC by flashing on and off. There is a short pause between flashes and a longer pause between digits. All DTC's displayed are two-digit numbers, with a four-second pause between codes.

An example of a DTC is as follows:
1. Lamp on for 2 seconds, then turns off.
2. Lamp flashes 4 times pauses and then flashes 1 time.
3. Lamp pauses for 4 seconds, flashes 4 times, pauses, then flashes 7 times.
4. The two DTC's are 41 and 47. Any number of DTC's can be displayed, as long as they are in memory. The lamp will flash until all stored DTC's are displayed, then it will flash a DTC 55 to indicate the test is complete.

Erasing Diagnostic Trouble Codes
- The DRB Scan Tool must be used to erase a DTC.