P129F
DTC P129F
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptor
DTC P129F
- Fuel Pump Speed Signal Incorrect
Diagnostic Fault Information
Circuit/System Description
The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is on. The voltage from the ECM to the FPCM remains active for 2 seconds, unless the engine is in crank or run. While this voltage is being received.
The FPCM provides a control enable input circuit to the FPCM relay to turn the 3-phase fuel pump ON and OFF. The control enable input circuit is switched to ground to turn ON the pump. The FPCM also sends a 400 HZ PWM on a signal circuit to the FPCM relay to control the fuel pump speed by varying the duty cycle of this signal.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
The purpose of the FPCM relay control frequency out-of-range diagnostic is to determine if the frequency of the pulse-width modulated FPCM relay control signal is not within its expected range (385 - 415 HZ). The above condition is present for greater than 12.5 milliseconds.
Action Taken When the DTC Sets
DTCs P129F are Type A DTCs.
Conditions for Clearing the DTC
* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear after 100 malfunction-free ignition cycles have occurred.
Diagnostic Aids
Using the Failure Records data may help locate an intermittent condition. If you cannot duplicate the DTC, the information in the Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can help determine how many ignition cycles that the diagnostic test reported a pass and/or a fail.
Reference Information
Schematic Reference
Engine Controls Schematics (LS3) (Electrical Diagrams)Engine Controls Schematics (LS7) (Electrical Diagrams)Engine Controls Schematics (LS9) (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Ignition ON, command the fuel pump ON and OFF using the scan tool ECM output control. The fuel pump should turn ON and OFF.
Circuit/System Testing
1. Ignition OFF, disconnect the X2 harness connector at the FPCM relay.
2. Ignition OFF, connect a DMM, set on the volt setting, between the PWM control circuit terminal 1 and ground.
3. Ignition ON, command the ECM fuel pump ON with a scan tool. The DMM reading should be between 4.5-5.5 V.
• If less than the specified range, test the PWM control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the FPCM.
• If greater than the specified range, test the PWM control circuit for a short to voltage. If the circuit tests normal, replace the FPCM.
4. If all circuits test normal, replace the FPCM relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Fuel Pump Flow Control Module Replacement (Service and Repair)
* Fuel Pump Flow Control Module Relay Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for FPCM replacement, setup, and programming