For 1990-2009 cars

### 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 IPC illuminating the Charge indicator.

### 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.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Starting and Charging Schematics
1 | Did you perform the Engine Electrical Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Electrical
2 |

1. Install a scan tool.
2. Start the engine.
3. Turn OFF all accessories, including headlamps.
4. With a scan tool, observe the GEN F-Terminal Signal parameter in the PCM data list .

Does the scan tool indicate that the GEN F-Terminal Signal parameter is within the specified value?

5-100 %

Go to Step 3

Go to Step 4

3 | With the scan tool command the GEN L-Terminal OFF. Does the scan tool indicate that the GEN F-Terminal Signal parameter is near the specified value? | 0 % | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 4
4 |

1. Turn OFF the ignition.
2. Disconnect the generator harness connector.
3. Start the engine.
4. Measure the voltage between the generator turn on signal circuit and a known good ground.
5. With the scan tool command the GEN L-Terminal ON and OFF.

Is the voltage equal to the first value with the generator OFF and near 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 10 | Go to Step 8
6 | Test the battery positive voltage circuit of the generator for an open or high resistance. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7
7 | 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 10 | Go to Charging System Test
8 | 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 10 | Go to Step 9
9 | IMPORTANT:: Perform the set up procedures for the PCM. Refer to Powertrain Control Module Programming in Engine Controls-3.4L. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls-3.4L. Did you complete the replacement? | -- | Go to Step 10 | --
10 |

1. Review and record the scan tool Fail Records data.
2. Use the scan tool in order to clear the DTC.
3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
4. Using the scan tool, observe the Specific DTC Information for DTC P0620 until the test runs.

Does the scan tool indicate that DTC P0620 failed this ignition?

--

Go to Step 2

System OK