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

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Generator Turn On Signal | P0621 | P0621 | P0621 | --

### Typical Scan Tool Data

#### GEN L-Terminal Ckt Short Gnd Test Status - ECM

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running. Parameter Normal Value: OK
Generator Turn On Signal | Fault | Not Run or OK | Not Run or OK

#### GEN L-Terminal Ckt Open Test Status - ECM

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running. Parameter Normal Value: Not Run or OK
Generator Turn On Signal | Not Run or OK | Not Run or Fault | Not Run or OK

#### GEN L-Terminal Ckt Short Volts Test Status - ECM

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Ignition ON. Parameter Normal Value: OK
Generator Turn On Signal | Not Run or OK | Not Run or OK | Fault

### Circuit/System Description

The engine control module (ECM) uses the generator turn on signal circuit, or L-terminal 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 signals 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 low voltage on the generator turn on signal circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage on the generator turn on signal circuit.

### Conditions for Running the DTC

The engine is running.

### Conditions for Setting the DTC

The ECM detects high or low voltage on the generator turn on signal circuit for 15 seconds.

### Action Taken When the DTC Sets

The charge indicator turns ON.

### Conditions for Clearing the DTC

• | The DTC will pass when the conditions for setting the DTC are no longer met for 1 second.

• | A 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

Component 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

Control Module References for scan tool information

### Circuit/System Verification

Engine running, observe the following scan tool ECM control circuit status parameters.

• | GEN L-Terminal Ckt Short Gnd Test Status

• | GEN L-Terminal Ckt Open Test Status

• | GEN L-Terminal Ckt Short Volts Test Status

Each parameter should read OK or Not Run.

### 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 1 and ground.

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

3. Engine running, command the GEN L-Terminal ON with a scan tool. Test for greater than 3.5 volts between the signal circuit terminal 1 and ground.

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

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Generator Replacement

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