P0626
DTC P0625 or P0626
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 Descriptors
DTC P0625
- Generator F-Terminal Circuit Low Voltage
DTC P0626
- Generator F-Terminal Circuit High Voltage
Diagnostic Fault Information
Circuit/System Description
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 percent. When the engine is running, the duty cycle should be between 5-99 percent.
Conditions for Running the DTC
P0625
* The engine is running.
* The engine speed is 3100 RPM +/- 15%.
P0626
* The engine is not running.
* The ignition is in the ON position.
Conditions for Setting the DTC
P0625
The ECM detects a pulse width modulated (PWM) signal less than 5 percent for 15 seconds.
P0626
The ECM detects a pulse width modulated (PWM) signal greater than 65 percent for 15 seconds.
Action Taken When the DTC Sets
DTC P0625 and P0626 are a C type DTCs.
Conditions for Clearing the DTC
DTC P0625 and P0626 are a C type DTCs.
Reference Information
Schematic Reference
Starting and Charging Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
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 Verification
Engine running, observe the scan tool GEN-F Terminal Signal parameter. The GEN-F Terminal Signal parameter should display between 5-99 percent.
Circuit/System Testing
1. Verify that a test lamp illuminates between the G13 generator B+ output circuit terminal A 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 G13 generator.
3. Ignition ON, verify the scan tool ECM GEN-F Terminal Signal parameter displays less than 5 percent.
• If greater than the specified range, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the K20 ECM.
4. Install a 3 A fused jumper wire between B+ and the signal circuit terminal 2.
5. Verify the scan tool ECM GEN-F Terminal Signal parameter displays greater than 95 percent.
• If less than the specified range, test the signal circuit terminal 2 for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
6. If the circuit tests normal replace the G13 generator.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Generator Replacement (Generator Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming