Diagnosis And Testing - On-Board Diagnostic System: Notes

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 40 good trips if the problem does not occur again.

The following procedures may be used to diagnose the charging system if:

• the check gauges lamp or battery lamp is illuminated with the engine running
• the voltmeter (if equipped) does not register properly
• an undercharged or overcharged battery condition occurs.

Remember that an undercharged battery is often caused by:

• accessories being left on with the engine not running
• a faulty or improperly adjusted switch that allows a lamp to stay on. Refer to Ignition-Off Draw Test Refer to BATTERY, STANDARD PROCEDURE .
• loose generator belt.