• 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 field duty cycle signal circuit, or F-terminal circuit, to monitor the duty cycle of the generator. The generator field duty cycle signal circuit connects to high side of the field windings in the generator. A pulse width modulated (PWM) high side driver in the voltage regulator turns the field windings ON and OFF. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of the generator field duty cycle signal circuit. When the ignition is ON and the engine is OFF, the ECM should detect a duty cycle near 0%. When the engine is running, the duty cycle should be between 5–99%.

• Ignition ON, engine OFF (Prior to Ignition ON, the ignition must have been OFF for at least 5 s)
• Engine running at less than 3,000 RPM

• DTC P0621 is not set.
• Ignition ON, engine OFF (Prior to Ignition ON, the ignition must have been OFF for at least 5 s), the ECM detects a PWM signal that is greater than 65% for 5 s
• Engine running at less than 3,000 RPM – The ECM detects a PWM signal that is less than 5% for 30 s

DTC P0622 is a C type DTC

• Ignition ON, Engine OFF – Low / no PWM signal detected
• Engine running – A 5–90% duty cycle is detected

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 for scan tool information

1. Engine running.
2. Verify the scan tool Engine Control Module Generator F-Terminal Signal parameter is between 5–90%.
• If not between 5–90%

  Refer to Circuit/System Testing.

• If between 5–90%
3. Verify the scan tool Engine Control Module Generator F-Terminal Signal parameter changes when commanding the headlamps ON and OFF.
• If the parameter does not change

  Refer to Circuit/System Testing.

• If the parameter changes
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
5. Verify the DTC does not set.
• If the DTC sets

  Refer to Circuit/System Testing.

• If the DTC does not set
6. All OK.

1. Verify 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. Remove the test lamp and disconnect the B+ cable at the G13 Generator.
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. Remove the test lamp, disconnect the battery negative cable, and disconnect the G13 Generator B+ cable.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the G13 Generator.
• If the test lamp illuminates
2. Disconnect the X2 harness connector at the G13 Generator, engine running.
3. Verify the scan tool Engine Control Module Generator F–Terminal Signal parameter is less than 5%.
• If 5% or greater
1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit terminal 2 and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K20 Engine Control Module.
• If less than 5%
4. Install a 3 A fused jumper wire between the signal circuit terminal 2 X1 and B+, engine running.
5. Verify the scan tool Engine Control Module Generator F–Terminal Signal parameter is greater than 95%.
• If 95% or less
1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the signal 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 signal circuit end to end.
• If 2 Ω or greater, repair the open/high resistance in the circuit
• If less than 2 Ω, replace the K20 Engine Control Module.
• If greater than 95%
6. Test or replace the G13 Generator.

Perform the Diagnostic Repair Verification after completing the repair.

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