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 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 the 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.
Conditions for Running the DTC
The ignition switch is in RUN.
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 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 Fuel Pump and Level Sensor Assembly
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 Control Module References 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
1. Verify that a test lamp illuminates between the G13 generator B+ terminal + X2 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for greater than 100 ohms between the B+ circuit and ground.
• If 100 ohms or less, repair the short to ground on the circuit.
• If greater than 100 ohms, replace the generator.
• If the test lamp illuminates
2. Ignition OFF, disconnect the X1 harness connector at the generator, engine Running, command the Generator L-Terminal Command ON with a scan tool.
3. Test for 3.5V or greater between the control circuit terminal listed below and ground.
* Terminal A X1 (LMU and LDT Engine)
* Terminal B X1 (L95, LXV, LXT, and LXV Engine)
• If less than 3.5V
1. Ignition OFF, disconnect the harness connectors at the ECM.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 ohms in the control circuit end to end.
• If greater the 2 ohms, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the ECM.
• If 3.5V or greater
1. Ignition OFF, disconnect the harness connectors at the ECM.
2. Test for less than 1 V between the control circuit and ground.
• If less than 1 V, replace the Generator.
• If 1 V or greater, repair the short to voltage on the circuit.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Generator Replacement (LUV) Generator Replacement (LUW) Service and Repair
* Control Module References Control Module References for ECM replacement, programming and setup