P0621
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
- Generator L-Terminal Circuit
Diagnostic Fault Information
Circuit/System Description
The engine control module (ECM) uses the charge indicator 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 charge indicator signal circuit.
Conditions for Running the DTC
* The engine is running.
* No generator, CKP sensors, CMP sensor DTCs are set.
Conditions for Setting the DTC
The charge indicator signal circuit is shorted to ground or shorted to voltage for 20 seconds.
Action Taken When the DTC Sets
* The charge indicator turns ON.
* The driver information center (DIC) displays the SERVICE BATTERY CHARGING SYSTEM message.
Conditions for Clearing the DTC
* The DTC will pass when the condition for setting the DTC is no longer present for 2 seconds.
* A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
* The charge indicator and DIC message will remain ON until the DTC passes or is cleared, even if the ignition is cycled.
Diagnostic Aids
A scan tool can be used to command the GEN L-Terminal circuit ON to 84% and OFF to 14% while the engine is running. Typical voltage values for the charge indicator control circuit are 10.5 V at 84% and 2.2 V at 14%.
Reference Information
Schematic Reference
Starting and Charging Schematics 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 K76)
1. Verify that a test lamp illuminates between the 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 ohm in the B+ circuit end to end.
• If 2 ohm or greater, repair the open/high resistance in the circuit.
• If less than 2 ohm, 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 ohm between the B+ circuit and ground.
• If 100 ohm or less, repair the short to ground on the circuit.
• If greater than 100 ohm, 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 1 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 ohm in the control circuit end to end.
• If greater the 2 ohm, repair the open/high resistance in the circuit.
• If less than 2 ohm, 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 G13 Generator.
• If 1 V or greater, repair the short to voltage on the circuit.
Circuit/System Testing - Dual Generators (K76)
1. Verify that a test lamp illuminates between the each generator B+ terminal A 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 ohm in each B+ circuit end to end.
• If 2 ohm or greater, repair the open/high resistance in the circuit.
• If less than 2 ohm, 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 ohm between the B+ circuit and ground.
• If 100 ohm or less, repair the short to ground on the circuit.
• If greater than 100 ohm, replace theappropriate 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 1 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 ohm in the control circuit end to end.
• If greater the 2 ohm, repair the open/high resistance in the circuit.
• If less than 2 ohm, 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. Engine running, test for 3.5 V or greater between signal circuit terminal 1 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 (V6) Generator ReplacementGenerator Replacement (V8) Generator ReplacementGenerator Replacement (Diesel) Generator Replacement
* Control Module References Control Module References for ECM replacement, setup, and programming.