Circuit Description
The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the Generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating conditions, the PCM can turn OFF the generator by turning OFF the 5 volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.
When this DTC sets, the PCM sends a class 2 serial data message to the instrument panel cluster (IPC) illuminating the Charge indicator lamp.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The generator turn on signal circuit 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 stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | The current DTC will clear when the diagnostic runs and does not fail. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
Diagnostic Aids
On vehicles equipped with a sense circuit to the voltage regulator, this circuit is used as a reference to control system voltage. The sense circuit must be operating correctly for the charging system to operate properly. All circuits at the generator should be tested for proper operation before replacing components. Refer to the schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Controls Connector End Views in Engine Controls - 3.4L, Electrical Center Identification Views in Wiring Systems or Engine Electrical Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Engine Electrical? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the voltage is above the specified value? | 13.0 V | Go to Step 7 | Go to Step 3 |
3 | With the scan tool command the GEN L-Terminal ON and OFF. Does the scan tool indicate that the voltage level changes with each command? | -- | Go to Step 7 | Go to Step 4 |
4 |
Is the voltage equal to the first value with the generator OFF and equal to the second value with the generator ON? | 0.0 V 5.0 V | Go to Step 6 | Go to Step 5 |
5 | Test the generator turn on signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
6 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
7 | Inspect for poor connections at the harness connector of the PCM. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
8 |
Important: Perform the set up procedures for the PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 3.4L. Did you complete the replacement? | -- | Go to Step 9 | |
9 |
Does the scan tool indicate that DTC P0620 failed this ignition? | -- | Go to Step 2 | System OK |
