P0621

DTC P0621

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

DTC Descriptor
DTC P0621
- Generator L-Terminal Circuit

Diagnostic Fault Information





Typical Scan Tool Data









Circuit/System Description

The engine control module (ECM) uses the generator turn ON control 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 control circuit. The ECM should detect low voltage on generator turn ON control 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 control circuit.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The ECM detects low voltage on the generator turn ON control circuit for 15 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

* The DTC passes when condition for setting the DTC is no longer present.
* The charge indicator and DIC message turn OFF when the DTC passes.

Reference Information
Schematic Reference

Starting and Charging Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Charging System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information

Circuit/System Verification

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

* GEN L-Terminal Ckt Short Gnd Test Status
* GEN L-Terminal Ckt Short Volts Test Status

The reading for each parameter should be OK.

Circuit/System Testing

1. Verify that a test lamp illuminates between the generator B+ terminal 1 X2 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

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

• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Engine running, command the GEN-L Terminal circuit ON to 85% with a scan tool. Test for greater than 3.5 V between the control circuit terminal 1 and ground.

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

5. If all circuits test normal, test or replace the generator.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Generator Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming.