DTC P0621

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

Circuit/System Description

 

The engine control module (ECM) uses the generator turn on signal 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 key ON and RUN tests to determine the status of the generator turn on signal circuit.

Conditions for Running the DTC

 

Key ON Test

     

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

 

     

The ignition is in RUN position.

 

     

The engine is not running.

Run Test

     

No generator, CKP sensors, CMP sensor DTCs are set.

 

     

The engine is running.

Conditions for Setting the DTC

 

     

During the key ON test, the ECM detects high voltage on the generator turn on signal circuit for at least 5 seconds.

 

     

During the RUN test, the ECM detects low voltage on the generator turn on signal circuit for at least 15 seconds.

Action Taken When the DTC Sets

 

     

The ECM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped.

 

     

The ECM will not illuminate the malfunction indicator lamp (MIL).

 

     

The ECM will store conditions, which were present when the DTC set as Failure Records data only.

Conditions for Clearing the DTC

 

     

The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

 

     

Using the scan tool Clear DTC Information function can clear the DTC.

Diagnostic Aids

 

On vehicles equipped with a sense circuit connected to the voltage regulator.This circuit must have voltage for the charging system to operate properly.This circuit is used as a reference to control system voltage. All circuits must be tested at the generator before replacing any components. refer to system schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.

Reference Information

 

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Engine Electrical Connector End Views

Electrical Information Reference

     

Circuit Testing

 

     

Connector Repairs

 

     

Testing for Intermittent Conditions and Poor Connections

 

     

Wiring Repairs

Scan Tool Reference

     

Scan Tool Data List for ECM

 

     

Scan Tool Data Definitions for ECM

Circuit/System Testing

 

  1. Ignition OFF, disconnect the harness connector at the generator.
  2. Ignition OFF, test for B+ between the generator sense circuit terminal D and ground.

If less than the specified range, test the generator sense circuit for a short to ground, an open/high resistance.

  1. Ignition ON, test for less than 1 volt between the generator turn on signal terminal B 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.

  1. Engine running, test for greater than 3.5 volts between the generator turn on signal and ground.

If less than the specified range, test the generator turn on signal circuit for a short to ground, an open/high resistance. If the circuit tests normal, replace the ECM.

  1. If the circuit test normal, replace the generator.

Repair Instructions

 

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

     

Control Module References for ECM replacement, setup, and programming

 

     

Generator Replacement