For 1990-2009 cars

## DTC P0621 3.6L (LY7)

### 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 : GEN L-Terminal Circuit Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit Description

The engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This commands the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect a high generator turn on signal circuit voltage. The ECM performs ignition key ON and RUN tests to determine the status of the generator turn ON signal circuit.

### Conditions for Running the DTC

• | Engine speed is more than 80 RPM.

• | The ignition 1 voltage is between 10-18 volts.

• | The ECM has commanded the generator turn ON signal circuit ON and OFF at least once during the ignition cycle.

• | DTC P0621 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

The ECM detects GEN L-Terminal circuit for an open, a short to ground, or a short to voltage.

### Action Taken When the DTC Sets

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

• | The ECM will only store the operating conditions as Failure Records data when setting the DTC.

### Conditions for Clearing the MIL/DTC

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

• | The DTC can be cleared by using the scan tool Clear DTC Information function.

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

Scan Tool Data Definitions

### Circuit/System Testing

1. Turn OFF the ignition. Disconnect the connection between the harness connector and the generator.
2. Turn ON the ignition, and 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 testing is normal, replace the ECM.

3. Start the engine. Test the voltage between the generator turn on signal circuit and the ground is more than 3.5 volts.

⇒ | If less than the specified value, test the generator turn on signal circuit for a short to ground, an open or a high resistance. If the circuit testing is normal, replace the ECM.

4. During the ignition Crank/Run testing, replace the generator if all circuits test normally.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Refer to Control Module References for ECM replacement, setup, and programming.

• | Refer to Generator Replacement.

## DTC P0621 4.6L (LH2)

### 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 : GEN L-Terminal Circuit Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit Description

The engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This commands the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect a high generator turn on signal circuit. The ECM performs ignition key ON and RUN tests to determine the status of the generator turn ON signal circuit.

### Conditions for Running the DTC

#### Ignition key ON Test

• | No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.

• | Ignition key is in RUN.

• | The engine is not running.

#### Run Test

• | No generator, CKP sensors or CMP sensors DTCs are set.

• | The engine is running.

### Conditions for Setting the DTC

During the Ignition Key ON test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 5 seconds. Or during the RUN test, the ECM detects a low signal voltage on the generator turn on signal circuit for at least 15 seconds.

### Action Taken When the DTC Sets

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

• | The ECM will only store the operating conditions as Failure Records data when setting the DTC.

### Conditions for Clearing the DTC

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

• | The DTC can be cleared by using the scan tool Clear DTC Information function.

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

#### Scan Tool Reference

Scan Tool Data List

Scan Tool Data Definitions

### Circuit/System Testing

1. Turn OFF the ignition. Disconnect the connection between the harness connector and the generator.
2. Turn ON the ignition, and 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 testing is normal, replace the ECM.

3. Start the engine. Test the voltage between the generator turn on signal circuit and the ground is more than 3.5 volts.

⇒ | If less than the specified value, test the generator turn on signal circuit for a short to ground, an open or a high resistance. If the circuit testing is normal, replace the ECM.

4. During the ignition Crank/Run testing, replace the generator if all circuits test normally.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Refer to Control Module References for ECM replacement, setup, and programming.

• | Refer to Generator Replacement.