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
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Generator L-Terminal Circuit
Diagnostic Fault Information
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 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 engine is running.
* No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.
Conditions for Setting the DTC
The ECM detects low voltage on the generator turn on signal circuit for 2 minutes.
Action Taken When the DTC Sets
The charge indicator turns ON.
Conditions for Clearing the DTC
The DTC passes when the malfunction is no longer present.
Reference Information
Schematic Reference
Starting and Charging Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (MN5)
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
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Programming and Relearning for scan tool information
Circuit/System Testing
LAT, LY7, or LCS Engine
1. Verify that a test lamp illuminates between the generator B+ terminal 1 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, engine OFF, test for less than 1 V between the generator turn on signal circuit terminal 1 X1 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.
4. Engine running, command the GEN L-Terminal ON to 85% with a scan tool. Test for greater than 3.5 V 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 or an open/high resistance. If the circuit tests normal, replace the ECM.
5. If the circuit tests normal, replace the generator.
LE5 or LZ4 Engine
1. Verify that a test lamp illuminates between the generator B+ terminal 1 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 X1 harness connector at the generator.
3. Ignition ON, test for 4.5-5.5 V between the control circuit terminals 1 X1 and ground.
• If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
• 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 ECM.
4. If the circuits test normal, replace the generator.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Generator Replacement (LEA) Service and RepairGenerator Replacement (LFW) Service and Repair
* Control Module References Programming and Relearning for ECM replacement, setup, and programming.