Circuit Description
The PCM Output (L) terminal to the alternator determines when the alternator will be turned off. It is on under all normal vehicle operating conditions except during low RPM conditions. The alternator is turned off during low RPM conditions to remove excess load from the engine.
The alternator Telltale lamp will illuminate any time the ignition is on and engine is not running. The Telltale will go out after the engine is running and the alternator is putting out the desired amperage.
Conditions for Running the DTC
| • | The engine is running. |
| • | The Voltage telltale is on. |
Conditions for Setting the DTC
| • | (L) terminal voltage is low while the PCM is commanding the generator on. |
| • | The above condition is present for more than 30 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. |
| • | The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Check for the following conditions:
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table:
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain OBD System Check performed? | -- | ||
2 |
Does the scan tool indicate that the Commanded Gen is on? | -- | ||
3 |
Command the Generator on with the scan tool while monitoring the J 39200 DMM. Does the voltage change from the first indicated value to the second indicated value? | 0.0V 5.0V | Go to Charging System Check | |
4 | Test the (L) circuit for an open or short to ground and repair if necessary. Refer to Wiring Repairs . Was a problem found? | -- | ||
5 | Test the (L) circuit for a short to voltage and repair if necessary. Refer to Wiring Repairs . Was a problem found? | -- | ||
6 | Inspect for a poor connection at the PCM and repair if necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals , and Connector Repairs . Was a problem found. | -- | ||
|
Important: : Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
8 |
Does the scan tool indicate DTC P0620 failed this ignition? | -- | System OK |
