Engine Electrical Diesel
DTC P0621 (Diesel)
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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Charge Indicator Control Circuit
Circuit/System Description
The ECM monitors the state of the charge indicator control circuit. The ECM should detect a low circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect a high circuit voltage. The ECM performs key ON and RUN tests to determine the status of the charge indicator control circuit.
During the key ON test, if the ECM detects a high circuit voltage, DTC P0621 will set. DTC P0621 will also set if, during the RUN test, the ECM detects a low circuit voltage. When the DTC sets, the IPC will illuminate the charge indicator or a warning message will be displayed in the driver information center (DIC) if equipped.
Conditions for Running the DTC
Key ON Test
* No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.
* The ignition is in RUN position.
* The engine is not running.
RUN Test
* No generator, CKP sensors, CMP sensor DTCs are set.
* The engine is running.
Conditions for Setting the DTC
During the key ON test, the ECM detects high voltage on the charge indicator control circuit for at least 5 seconds. OR during the RUN test the ECM detects low voltage on the charge indicator control circuit for at least 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.
Reference Information
Schematic Reference
Starting and Charging Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
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 Testing - Single Generator (w/o KD9)
1. Verify that a test lamp illuminates between the G13 generator B+ terminal 1 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, ignition ON.
3. Test for 3.5V or greater between the control circuit terminal B X1 and ground.
• 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 than 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.
Circuit/System Testing- Dual generators (w/ KD9)
1. Verify that a test lamp illuminates between the each generator B+ terminal 1 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 each 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 appropriate generator.
• If the test lamp illuminates
2. Ignition OFF, disconnect the X1 harness connectors at both generators, ignition ON.
3. Test for 3.5V or greater between the control circuit terminal B X1 and ground.
• 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 than 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 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V
3. Ignition OFF, connect X1 harness connector at the auxiliary generator, Ignition ON.
4. Test for less than 1 V between the control circuit and ground.
• If greater than 1 V, replace the auxiliary generator.
• If less than 1 V
5. Ignition OFF, connect the harness connectors at the ECM.
6. Engine running, test for 3.5 V or greater between the generator control circuit terminal B X1 and ground.
• If less than 3.5 V, test or replace the auxiliary generator.
• If 3.5 V or greater, test or replace the generator.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Generator Replacement (V8) Service and RepairGenerator Replacement (V6) Service and RepairGenerator Replacement (Diesel) Service and Repair
* Auxiliary Generator Replacement (KD9) Service and Repair
* Control Module References Control Module References for ECM replacement, setup, and programming