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 engine control module (ECM)/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 ECM/PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM/PCM monitors the state of the circuit. The ECM/PCM should detect low voltage on circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM/PCM should detect high voltage on the circuit. The ECM/PCM performs key a ON and RUN test to determine the status of the circuit.

### Conditions for Running the DTC

#### Key ON Test

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

• | The ignition is in RUN position.

• | The engine is not running.

#### RUN Test

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

• | The engine is running.

### Conditions for Setting the DTC

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

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

### Action Taken When the DTC Sets

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

• | The ECM/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.

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### Connector End View Reference

Engine Electrical Connector End Views

#### Description and Operation

Charging System Description and Operation

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

⇒ | If greater than the specified range, test the circuit for a short to voltage. If the circuit tests normal, replace the ECM/PCM.

3. Engine running, test for greater than 3.5 volts between the generator turn ON signal circuit terminal B and ground.

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

4. If the circuit test normal, replace the generator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Generator Replacement for generator replacement

• | Control Module References for ECM/PCM replacement, setup, and programming