Generator Field Not Switching Properly

WHEN MONITORED
With the ignition key on and the engine running.

SET CONDITION
When the PCM tries to regulate the generator field with no result during monitoring.

THEORY OF OPERATION
The PCM tries to maintain a system voltage between 12.9 volts and 15.0 volts.

The voltage determined by the PCM as the final goal for the charging system is called "Control Voltage".

- Control voltage is determined from the battery temperature sensor or ambient sensor and the system voltage sensed at PCM cavity 3.

The PCM continuously compares control voltage to the sensed voltage while the engine is running.

- If the sensed voltage is less than the control voltage, the PCM supplies more ground to the field circuit, (allowing more current to flow).

- If the sensed voltage is more than the control voltage, the PCM supplies less ground to the field circuit, (allowing less current to flow).

PROBABLE CAUSES
- Field Driver Circuit Open Or Shorted
- Generator Internal Open Or Short
- PCM Failure