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Diagnostic Test - FPCM System Command Circuit Faults (P025A, P027A)

TECH TIP:  The FPCM DTCs will set incorrectly for some vehicles/model years due to incorrect calibrations. For those vehicles it is best to perform the "COMPLETE FUEL PUMP CONTROL MODULE SYSTEM TESTING (NOT DTC SPECIFIC)" diagnostic procedure. Refer to the "KNOW ISSUES" service information above for a list of the vehicles with incorrect calibrations.

COMMAND CIRCUIT OPEN/LOW/HIGH (P025A, P027A): 

The FPCM PWM Command circuit is a 12 volt PWM signal. This fault will set when it is detected that the command circuit between the PCM and FPCM is open, stuck low (shorted to ground) or stuck high (shorted to voltage). For a detailed description on the functionality of the command circuit, read the PCM component functional description service information above.

NOTE:

With an open command circuit, the PCM internal driver will show a pulse width signal of approximately 2.5v if checking at the PCM connector with the Mopar Scope. This is picking up voltage from the internal driver device that is still trying to pulse the duty cycle to the FPCM. This can be useful when performing diagnostics on the command circuitry.

Listed below are test methods using the Mopar Scope and traditional testing with a meter.

TESTING THE COMMAND CIRCUIT USING THE MOPAR SCOPE (PREFERRED METHOD): 

Using the Mopar Scope is the preferred and best method for diagnosing the FPCM and circuits. The circuits can be monitored one at a time or all together using all four channels of the scope. Crank or start the engine while monitoring the following command circuit. The command circuit can be tested at the FPCM or at the PCM using the GPEC Adaptor connected in-line. Both results are described below.

SCOPE LEAD CONNECTED AT THE FPCM

  1. If the PWM Command circuit is functioning normally the signal should have a 12v duty cycle between 11% and 89%.
    • If the command circuit is functioning as described above the command circuit is not the cause of the issue.
    • GC0201851Courtesy of CHRYSLER GROUP, LLC

      This pattern was shows the result of a short to ground in the command circuit

      Blue Channel - Feedback circuit
      Red Channel - Fuel pump output circuit
      Green Channel - Command circuit
  2. If the PWM Command circuit is reading a constant 0 volts, it would indicate that the control circuit is shorted to ground.
    • Test and repair the short to ground in the command circuit.
    GC0201453Courtesy of CHRYSLER GROUP, LLC

    This is a pattern of an open command circuit with yellow scope lead connected on the FPCM side of the open and the green scope lead connected on the PCM side of the open

    Blue Channel - Feedback circuit
    Yellow Channel - Command circuit on the FPCM side of the open
    Green Channel - Command circuit on the PCM side of the open
  3. If the PWM Command circuit is a reading a constant battery voltage, it would indicate an open in the command circuit or the PCM internal driver is faulty.
    • Isolate and measure the resistance of the command circuit. If the circuit is open or has high resistance repair the circuit. If the circuit has less than 5.0 Ohms of resistance, the PCM driver is faulty. Replace the powertrain control module in accordance with the service information.
    GC0201453Courtesy of CHRYSLER GROUP, LLC

    This is a pattern of an open command circuit with yellow scope lead connected on the FPCM side of the open and the green scope lead connected on the PCM side of the open

    Blue Channel - Feedback circuit
    Yellow Channel - Command circuit on the FPCM side of the open
    Green Channel - Command circuit on the PCM side of the open
  4. If the PWM Command circuit is duty cycling, but the voltage is approximately 2.5v instead of the normal 12v duty cycle, it indicates that the command circuit and PCM internal driver are good. The FPCM is not producing the 12v output on the command circuit.
    • Verify that the relay output battery supply to the FPCM is constant and the FPCM ground circuit is good. If both circuits test good replace the fuel pump control module in accordance with the service information.

SCOPE LEAD CONNECTED AT THE GPEC ADAPTOR IN-LINE WITH THE PCM

  1. If the PWM Command circuit is functioning normally the signal should have a 12v duty cycle between 11% and 89%.
    • If the command circuit is functioning as described above the command circuit is not the cause of the issue.
    GC0201851Courtesy of CHRYSLER GROUP, LLC

    This pattern was taken at the FPCM showing the result of a short to ground in the command circuit

    Blue Channel - Feedback circuit
    Red Channel - Fuel pump output circuit
    Green Channel - Command circuit
  2. If the PWM Command circuit is reading a constant 0 volts, it would indicate that the command circuit is shorted to ground.
    • Test and repair the short to ground in the command circuit.
    GC0201453Courtesy of CHRYSLER GROUP, LLC

    This is a pattern of an open command circuit with yellow scope lead connected on the FPCM side of the open and the green scope lead connected on the PCM side of the open

    Blue Channel - Feedback circuit
    Yellow Channel - Command circuit on the FPCM side of the open
    Green Channel - Command circuit on the PCM side of the open
  3. If the PWM Command circuit is a reading a constant battery voltage, it indicates the command circuit and FPCM output are good. The PCM internal driver is faulty.
    • Replace the powertrain control module in accordance with the service information.
    GC0201453Courtesy of CHRYSLER GROUP, LLC

    This is a pattern of an open command circuit with yellow scope lead connected on the FPCM side of the open and the green scope lead connected on the PCM side of the open

    Blue Channel - Feedback circuit
    Yellow Channel - Command circuit on the FPCM side of the open
    Green Channel - Command circuit on the PCM side of the open
  4. If the PWM Command circuit is duty cycling, but the voltage is approximately 2.5v instead of the normal 12v duty cycle, it indicates that the PCM internal driver is good. There is an open in the command circuit or the FPCM is not producing the 12v output on the command circuit.

    • Isolate and measure the resistance of the command circuit. If the circuit is open or has high resistance repair the circuit. If the circuit has less than 5.0 Ohms of resistance, the FPCM output is faulty. Replace the fuel pump control module in accordance with the service information.

TESTING THE COMMAND CIRCUIT USING A METER: 

  1. Check for continuity between ground and the FPCM PWM command circuit. There should be no continuity between ground and the FPCM PWM command circuit
    1. If the FPCM PWM command circuit shows continuity to ground, repair the FPCM PWM command circuit for a short to ground.
    2. If the FPCM PWM command circuit does not show continuity to ground, continue to step 2. 
  2. Disconnect the PCM and FPCM harness connectors. Check for continuity between the FPCM PWM command circuit and all other circuits at the PCM harness connector. There should be no continuity between the FPCM PWM command circuit and any other circuit.
    1. If the FPCM PWM command circuit shows continuity with another circuit, repair the FPCM PWM command circuit for a short to the other circuit.
    2. If the FPCM PWM command circuit does not show continuity to any other circuit, continue to step 3. 
  3. Measure the resistance of the FPCM PWM command circuit between the FPCM harness connector and PCM harness connector. The resistance should typically be below 3.0 Ohms.
    1. If the resistance is above 3.0 Ohms, repair the FPCM PWM command circuit for high resistance.
    2. If the FPCM PWM command circuit tests good, the issue could be either an intermittent condition, poor pin fit at a connector, or a calibration issue setting the incorrect DTC.
      • If the terminals appear good and an intermittent issue isn't found perform the "DIAGNOSTIC TEST - COMPLETE FUEL PUMP CONTROL MODULE SYSTEM TESTING (NOT DTC SPECIFIC)" diagnostic to check the entire system operation.
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