Chart C-19 PCM Controlled Generator (Functional Check)

Chart C-19 PCM Controlled Generator (Functional Check):

PCM Controlled Generator (Functional Check):

CIRCUIT DESCRIPTION
The generator communicates to the Powertrain Control Module (PCM) over two lines, the "L" or Lamp circuit and the "F" or Field circuit. The PCM uses the "L" circuit to monitor faults in the charging system. The "F" circuit is used by the PCM to monitor the duty cycle or load of the generator. The PCM will then adjust idle speed according to generator load.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the "Battery" symbol is not operating, either a shorted circuit or the Instrument Panel Cluster (IPC) is at fault. This step determines whether the "L" circuit, generator IPC is at fault.
2. If the charging system is not functioning, system voltage cannot be maintained above 12.0 volts. Be sure to turn "OFF" all accessories to insure that the system voltage is not being drawn down by an accessory that normally draws large current.
3. Even when the engine is not running, the generator duty cycle will display above 5%. If the generator duty cycle reads 0%, then the "F" circuit is either open or shorted to ground.
4. If the "L" circuit is not shorted to ground, the volts telltale will go out until the next key cycle when the test light is proved into terminal "L". Be careful not to prove terminal "F" with the test light, this will turn off the volts talltale whether or not the "L" circuit is shorted.
5. The PCM supplies about 5 volts to the generator. If voltage is available to the generator at this terminal, then the PCM and wiring are OK.

DIAGNOSTIC AIDS
^ If CKT 23 is shorted to voltage, the volts telltale will operate normally. However, the Tech 1 scan tool "GEN F" will display a generator duty cycle near 100%. Check CKT 23 for a short to voltage. If OK, generator may be faulty, refer to Section "6D3".
^ An "Intermittent" problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.

Check for:

Poor connection or damaged harness
Inspect PCM harness for open or short to ground in CKT 25, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections, and damaged harness.