For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0621 : Generator L- Terminal Circuit

### Circuit/System Description

The powertrain control module (PCM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the PCM applies a voltage to the voltage regulator. When the PCM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the PCM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.

The PCM monitors the state of the generator turn on signal circuit. With the engine running, the PCM should detect a high generator turn on signal circuit, or when the charging system malfunctions. If the PCM detects a low generator turn on signal circuit, DTC P0621 will set.

### Conditions for Running the DTC

#### Key ON Test

• | The ignition is in RUN position.

• | The engine is not running.

#### RUN Test

• | The engine is running.

• | The engine speed is less than 3,000 RPM.

### Conditions for Setting the DTC

• | During the key ON test, the PCM detects high voltage on the generator turn on signal circuit for at least 5 seconds.

• | During the RUN test the PCM detects low voltage on the generator turn on signal circuit for at least 15 seconds.

### Action Taken When the DTC Sets

• | The PCM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped.

• | The PCM will not illuminate the malfunction indicator lamp (MIL).

• | The PCM will store conditions, which were present when the DTC set as Fail Records data only.

### Conditions for Clearing the DTC

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | Using the scan tool Clear DTC Information function can clear the DTC.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the generator.
2. Ignition ON, test for less than 1 volt between the generator turn on signal and ground.

⇒ | If greater than the specified range, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the PCM.

3. Engine Running, test for greater than 3.5 volts between the generator turn on signal and ground.

⇒ | If less than the specified range, test the generator turn on signal circuit for a short to ground, an open or a high resistance. If the circuit tests normal, replace the PCM.

4. If the circuit tests normal during the ignition ON/Run test, replace the generator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for PCM replacement, setup, and programming