P0621

DTC P0621

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy 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 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 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. The ECM performs tests to determine the status of the generator turn on signal circuit.


Conditions for Running the DTC

* No generator, CKP sensors, CMP sensor DTCs are set.
* 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 ECM will command the charge indicator to be illuminated on the instrument panel cluster (IPC).
* The ECM will not illuminate the malfunction indicator lamp (MIL).
* The ECM will store conditions, which were present when the DTC set as Fail Records data only.



Conditions for Clearing the DTC

* A current DTC will clear when the conditions for setting the DTC are no longer met.
* A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.



Reference Information
Schematic Reference

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

Component Connector End Views (Connector Views)
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

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 generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

3. Engine running, command the L-Terminal ON to 85% with a scan tool. Test for greater than 3 volts on the generator turn on signal circuit.

• If less than the specified range, test the generator turn on 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, replace the generator.



Repair Instructions

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

* Generator Replacement (With L61 and LE5) (Service and Repair)Generator Replacement (With LNF) (Service and Repair)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming