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





Circuit/System Description

The engine control module (ECM) uses the generator turn ON control 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 controls 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 ignition ON, engine OFF for ignition on test.
* The engine is running for the run test.

Conditions for Setting the DTC

* During the ignition on test, the ECM detects voltage on the generator turn on control circuit for 5 seconds.
* During the run test, the ECM detects low voltage on the generator turn on control circuit for 15 seconds.

Action Taken When the DTC Sets

DTC P0621 is a C type DTC.

Conditions for Clearing the DTC

DTC P0621 is a C type DTC.

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 Testing

LLT Engine
1. Verify that a test lamp illuminates between the G13 generator B+ output circuit A 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 G13 generator.
3. Ignition ON, test for less than 1 V between the 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 K20 ECM.

4. Engine running, 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 K20 ECM.

5. If the circuit tests normal, replace the G13 generator.

L99 or LS3 Engine
1. Verify that a test lamp illuminates between the G13 generator B+ terminal A 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 G13 generator.
3. Ignition ON, test for 4.5-5.5 V between the 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.
• 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.

4. If the circuits test normal, replace the G13 generator.

Repair Instructions

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

* Generator Replacement (LLT) (Generator Replacement)Generator Replacement (LS3/L99) (Generator Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming