P0621

DTC P0621 (Diesel)

Diagnostic Instructions

* Perform theDiagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* ReviewStrategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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 charge indicator 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 charge indicator signal circuit.


Conditions for Running the DTC

* The engine is running.
* No generator, CKP sensors, CMP sensor DTCs are set.



Conditions for Setting the DTC

The charge indicator signal circuit is shorted to ground or shorted to voltage for 20 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 will pass when the condition for setting the DTC is no longer present for 2 seconds.
* A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
* The charge indicator and DIC message will remain ON until the DTC passes or is cleared, even if the ignition is cycled.



Diagnostic Aids

A scan tool can be used to command the GEN L-Terminal circuit ON to 84% and OFF to 14% while the engine is running. Typical voltage values for the charge indicator control circuit are 10.5 V at 84% and 2.2 V at 14%.


Reference Information
Schematic Reference

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

Component Connector End Views (Connector Views)
Description and Operation

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

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

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


Circuit/System Testing - Single Generator (w/o K76)

1. Ignition OFF, disconnect the X1 harness connector at the generator.
2. Ignition ON, test for less than 1 V between the 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 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.



Circuit/System Testing - Dual Generators (K76)

1. Ignition OFF, disconnect the X1 harness connectors at both generators.
2. Ignition ON, engine OFF, test for less than 1 V between the signal circuit terminal 1 of either generator harness 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 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. Ignition OFF, connect the X1 harness connector at the auxiliary generator.
5. Ignition ON, engine OFF, test for less than 1 V between the signal circuit terminal 1 of the primary generator harness and ground.

• If greater than the specified range, replace the auxiliary generator.

6. Engine running, test for greater than 3.5 V between the signal circuit terminal 1 and ground.

• If less than the specified range, replace the auxiliary generator.

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



Repair Instructions

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

* Generator Replacement (4.3L) (Generator Replacement)Generator Replacement (6.6L) (Generator Replacement)Generator Replacement (4.8L, 5.3L, 6.0L, and 6.2L) (Generator Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming.