P0621
DTC P0621
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptor
DTC P0621
- Generator L-Terminal Circuit
Diagnostic Fault Information
Typical Scan Tool Data
Circuit/System Description
The engine control module (ECM) uses the generator turn on control 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.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The ECM detects high or low voltage on the generator turn on control circuit for 15 seconds.
Action Taken When the DTC Sets
The charge indicator turns ON.
Conditions for Clearing the DTC
* The DTC will pass when the conditions for setting the DTC are no longer met for 1 second.
* A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
Reference Information
Schematic Reference
Starting and Charging Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Charging System Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Engine running, observe the following scan tool ECM control circuit status parameters.
* GEN L-Terminal Ckt Short Gnd Test Status
* GEN L-Terminal Ckt Open Test Status
* GEN L-Terminal Ckt Short Volts Test Status
Each parameter should read OK or Not Run.
Circuit/System Testing
LY7 Engine
1. Verify that a test lamp illuminates between the G13 generator B+ terminal + X2 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
2. Ignition OFF, disconnect the harness connector at the generator.
3. Ignition ON, test for less than 1 V between the control circuit terminal 1 and ground.
• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.
4. Engine running, test for greater than 3.5 V between the control circuit terminal 1 and ground.
• If less than the specified range, test the control circuit for a short to ground, an open or a high resistance. If the circuit tests normal, replace the K20 ECM.
5. If the circuit tests normal, test or replace the G13 generator.
LE5, LZ4 or LZ9 Engine
1. Verify that a test lamp illuminates between the G13 generator B+ terminal + X2 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
2. Ignition OFF, disconnect the harness connector at the generator.
3. Ignition ON, test for 4.5-5.5 V between the control circuit terminals listed below and ground:
* Terminal 1 (LE5)
* Terminal B (LZ4, LZ9)
• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.
• If less than the specified range, test the control circuit for a short to ground, an open or a high resistance. If the circuit tests normal, replace the K20 ECM.
4. If the circuit tests normal, test or replace the G13 generator.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Generator Replacement (Generator Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming