Circuit Description
The PCM Output (L) terminal to the generator determines when the generator will be turned off. The generator is on under all normal vehicle operating conditions except during low RPM conditions. The generator is turned off during low RPM conditions to remove excess load from the engine.
The PCM Input Field (F) terminal from the generator provides a 400 Hz PWM signal to the PCM. The duty cycle of the F terminal mimics the duty cycle of the field coils in the generator. Thus, the F terminal duty cycle indicates the relative electrical load on the generator.
The generator telltale lamp will illuminate any time the ignition is on and the engine is not running. The telltale will turn off after the engine is running and the generator is putting out the desired amperage.
Diagnostic Aids
Check for the following conditions:
| • | A poor connection at the PCM or the generator. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Use a corresponding mating terminal to test for proper terminal tension. Refer to Testing for Intermittent Conditions and Poor Connections Connector Repairs and to Wiring Repairs in Wiring Systems. |
| • | A damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition on and observe voltmeter connected to the generator circuits at the PCM harness connector while moving the connectors and the wiring harnesses related to the generator control circuit. A change in voltage will indicate the location of the fault. Refer to Connector Repairs and to Wiring Repairs in Wiring Systems. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Does the scan tool indicate that the Generator PWM is within the indicated range? | 5% - 95% | ||
3 |
Command the generator ON with the scan tool while monitoring the DMM. Does the voltage change from the first specified value to the second specified value? | 0 V 5 V | ||
4 |
Is the reading affected? | -- | ||
5 | Test the (L) circuit for an open or short to ground and repair if necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||
6 | Test the (L) circuit for a short to voltage and repair if necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||
7 | Test the (F) circuit for an open or short to ground and repair if necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||
8 | Test the (F) circuit for a short to voltage and repair if necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||
9 | Check for a poor connection at the PCM and repair if necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. was a problem found. | -- | ||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
11 |
Does the scan tool indicate DTC P0121 failed this ignition? | -- | System OK |
