P0621

DTC P0621

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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

Diagnostic Fault Information






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 the ignition ON and RUN tests to determine the status of the generator turn on signal circuit.

Conditions for Running the DTC

* No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.
* The ignition ON, engine OFF for the ignition on test.
* The engine running for the run test.

Conditions for Setting the DTC

* During the ignition ON test, the ECM detects high voltage on the generator turn on signal circuit for 5 seconds.
* During the RUN test, the ECM detects low voltage on the generator turn on signal 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.

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 X1 terminal 1 and ground.

• If greater than the specified value, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

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

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

4. If the circuit tests normal, test or replace the generator.

Repair Instructions

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

* Generator Replacement (LS4) Generator Replacement (RPOs LZE/LZ4/LZ8)