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
--- | --- | --- | --- | ---
B+ | P0625 | P0625 | -- | --
Field Duty Cycle Signal | P0625 | P0625 | P0626 | --
Turn On Signal | P0621 | -- | P0621 | --

### 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.

### Conditions for Running the DTC

• | The engine is running.

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

### Conditions for Setting the DTC

The ECM detects high or low voltage on the turn on signal circuit for 7 seconds.

### Action Taken When the DTC Sets

• | The charge indicator turns ON.

• | The driver information center (DIC) displays the SERVICE BATTERY CHARGING SYSTEM message.

### Conditions for Clearing the DTC

DTC P0621 is a type C DTC.

### 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

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the generator.
2. Ignition ON, test for less than 1 V between the 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, test for greater than 3.5 V between the turn on signal circuit terminal 1 and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground or an open/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.