• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

The engine control module (ECM) uses the generator turn ON control 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 controls the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn ON control circuit. The ECM should detect low voltage on generator turn on control 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 control circuit.

• The ignition ON, engine OFF for ignition on test.
• The engine is running for the run test.

• During the ignition on test, the ECM detects voltage on the generator turn on control circuit for 5 seconds.
• During the run test, the ECM detects low voltage on the generator turn on control circuit for 15 seconds.

DTC P0621 is a C type DTC.

DTC P0621 is a C type DTC.

Starting and Charging Schematics

Master Electrical Component List

Charging System Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References

1. Verify that a test lamp illuminates between the G13 Generator B+ circuit terminal A X1, A X2 (LYX), AX2 (LH7/LTG), B X1 ,1 X1 or 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 Ω in the B+ circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit.
• If less than 2 Ω, 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 Ω between the B+ circuit and ground.
• If 100 Ω or less, repair the short to ground on the circuit.
• If greater than 100 Ω, replace the generator.
• If the test lamp illuminates
2. Ignition OFF, disconnect the X2 harness connector at the G13 Generator, engine running.
3. Test for 1 V or greater between the control circuit terminal 1 X1 and ground.
• If less than 1 V
1. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module.
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 Ω in the control circuit end to end.
• If greater the 2 Ω, repair the open/high resistance in the circuit.
• If less than 2 Ω, replace the K20 Engine Control Module.
• If 1 V or greater
4. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module, ignition ON.
5. Test for less than 1 V between the control circuit and ground.
• If greater than 1 V,

  Repair the short to voltage on the circuit.

• If 1 V or less
6. Test or replace the G13 Generator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Generator Replacement
• Control Module References for control module replacement, programming, and setup