Symptoms

- Engine Light ON (or Service Engine Soon Warning Light)

Possible Causes

- Generator circuit - Generator circuit short to fround - Generator circuit open/high Resistance - Generator circuit short to voltage - Bad generator/alternator - Faulty ECM

When Detected

- During the Ignition ON test, the ECM detects high voltage on the generator turn on signal circuit for 5 seconds. - During the RUN test, the ECM detects low voltage on the generator turn on signal circuit for 15 seconds.

Tech Notes

The ECM is detecting a high turn-on voltage at times. Possible causes could be the alternator or the ECM.

Description

The Engine Control Module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect low voltage on generator turn on signal circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage on the generator turn on signal circuit. The ECM performs Ignition ON and RUN tests to determine the status of the generator turn on signal circuit.