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DTC P0621

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

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
B+

P0625

P0621

-

-

Control

P0621

P0621

P0621

-

Signal

P0625

P0625

P0626

P0625



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 s.

• During the run test, the ECM detects low voltage on the generator turn on control circuit for 15 s.


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

Connector End View Reference

Component Connector End Views

Description and Operation

Charging System Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing


1. Verify that a test lamp illuminates between the G13 Generator B+ terminal 1 X1 and ground.

2. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, disconnect the X1 harness connector at the G13 Generator.

4. Ignition ON, test for less than 1 V between the control circuit terminal 1 and ground.

5. If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module.

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

7. 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 Engine Control Module.

8. If the circuit tests normal, replace the G13 Generator.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Refer to Generator Replacement (Diesel) Generator Replacement (LAU/A28NER) Generator Replacement (LLU/A16LET) Generator Replacement (LHU/A20NFT) .

• Control Module References for ECM replacement, setup, and programming