GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Impala 🢒 Engine 🢒 Engine Electrical 🢒 DTC P0620

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 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.

Step

Action

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. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, monitor the DTC Information for DTC P0620 in Engine Controls.

Does the scan tool indicate that DTC P0620 has passed?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 4

4

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 6

Go to Step 5

5

Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Programming in Engine Controls -3.4L or Powertrain Control Module Programming in Engine Controls- 3.8L.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls -3.4L or Powertrain Control Module Replacement in Engine Controls -3.8L.

Did you complete the repair?

Go to Step 6

Go to Step 6

6
  1. Review and record the scan tool Fail Records data.
  2. Clear any DTCs.
  3. Operate the vehicle within the Fail Records conditions as noted.
  4. Using a scan tool, monitor the Specific DTC info for DTC P0620.

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

Go to Step 2

System OK