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Diagnostic Test - Communication And FPCM Internal Faults (P1205, P120A, U0109, U016C)

FPCM INTERNAL PERFORMANCE (P1205, P120A): 

  1. The FPCM is reporting that it has lost the capability of performing fault detection on the system.
    1. Replace the FPCM in accordance with the service information.
NOTE:

If the P0627-Fuel Pump Relay Control Circuit fault is present, diagnose that DTC before continuing.

LOSS OF COMMUNICATION DIAGNOSTICS (U0109, U016C): 

The PCM can lose communication with the FPCM if the FPCM does not power up or the FPCM PWM Feedback circuit is open or shorted. The FPCM is powered when the PCM energizes the Fuel Pump Relay. For a detailed description on the functionality of the feedback circuit, read the FPCM component functional description information above. The preferred method of testing is with the Mopar scope. The FPCM power and ground can also be tested using a load test and DVOM. Choose one of the two methods below to test the system.

NOTE:

The PCM will command the highest command duty cycle when it cannot receive feedback from the FPCM due to an issue with the feedback circuit. The fuel pump should still operate when the communication is lost between the FPCM and PCM due to a feedback signal circuit issue. Typically the output voltage to the fuel pump will be higher than during normal operation.

TESTING THE BATTERY SUPPLY AND FEEDBACK USING A MOPAR SCOPE 

- The feedback 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. Using the wiring information as a guide, check the fuse that supplies power to FPCM through the Fuel Pump Relay. Verify the fuse is not open and has a good connection with the terminals in the PDC.
    1. If the fuse is good, continue to step 2. 
    2. If the fuse is open, check the Fuel Pump Relay Output circuit and the Fuel Pump PWM Control circuit for a short to ground.
      NOTE:

      The Fuel Pump PWM Control circuit voltage comes from the Fuel Pump Relay Output circuit through the FPCM.

  2. Back probe and connect the scope lead to the feedback signal at the FPCM.
    1. If the FPCM PWM Feedback circuit is functioning normally the signal should have a 5v duty cycle between 3% and 97%.
      • If the feedback circuit is functioning as described above the feedback circuit is not the cause of the issue.
    2. If the PWM feedback 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 feedback circuit.
    3. If the PWM feedback circuit is reading a constant 5.0 volts, it would indicate that FPCM internal driver is faulty.
      • Replace the fuel pump control module in accordance with the service information.
        GC0201229Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit on the FPCM side of the open
        Yellow Channel - Feedback circuit on the PCM side of the open
        Green Channel - Command circuit
        Red Channel - Fuel pump output circuit
    4. An open or partially open ground circuit can effect the feedback pattern in different ways. The PWM feedback circuit may read a constant voltage approximately 6.5 volts, or it could be a pulsed voltage between 5.0 volts and 8.0 volts when the FPCM ground circuit is open.
      • Test and repair the FPCM ground circuit for an open or high resistance.
        GC0200585Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit
        Red Channel - Fuel pump output circuit
        Green Channel - Command circuit
    5. If the PWM feedback circuit is duty cycling between approximately 0.3 and 0.6v instead of the normal 5v duty cycle, it indicates that the FPCM internal driver is good. Either the feedback circuit is open or the PCM is not producing the 5v output on the feedback 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 output driver is faulty. Replace the powertrain control module in accordance with the service information.
        NOTE:

        Another way to test the output and circuit is to connect a scope lead to the PCM connector using the GPEC Adaptor tool. If the 5v output is present at the PCM connector, but not at the FPCM, the PCM is good and the feedback circuit is open.

        GC0201407Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit on the FPCM side of the open

SCOPE LEAD CONNECTED AT THE PCM WITH THE GPEC ADAPTOR 

  1. Using the wiring information as a guide, check the fuse that supplies power to FPCM through the Fuel Pump Relay. Verify the fuse is not open and has a good connection with the terminals in the PDC.
    1. If the fuse is good, continue to step 2. 
    2. If the fuse is open, check the Fuel Pump Relay Output circuit and the Fuel Pump PWM Control circuit for a short to ground.
      NOTE:

      The Fuel Pump PWM Control circuit voltage comes from the Fuel Pump Relay Output circuit through the FPCM.

  2. Connect the GPEC Adaptor in-line with the PCM harness connector. Connect the scope lead to the feedback signal at the GPEC Adaptor.
    1. If the FPCM PWM Feedback circuit is functioning normally the signal should have a 5v duty cycle between 3% and 97%.
      • If the feedback circuit is functioning as described above the feedback circuit is not the cause of the issue.
    2. If the PWM feedback 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 feedback circuit.
    3. If the PWM feedback circuit is reading a constant 5.0 volts, it would indicate that the feedback circuit is open or the FPCM internal driver is faulty.
      • 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 driver is faulty. Replace the fuel pump control module in accordance with the service information.
        GC0201229Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit on the FPCM side of the open
        Yellow Channel - Feedback circuit on the PCM side of the open
        Green Channel - Command circuit
        Red Channel - Fuel pump output circuit
    4. If the PWM feedback circuit is reading a constant voltage approximately 6.5 volts, it would indicate that the FPCM ground circuit is open.
      • Test and repair the FPCM ground circuit for an open or high resistance.
        GC0200585Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit
        Red Channel - Fuel pump output circuit
        Green Channel - Command circuit
    5. If the PWM feedback circuit is duty cycling between approximately 0.3v and 0.6v instead of the normal 5v duty cycle, it indicates that the feedback circuit and FPCM internal driver is good. The PCM is not producing the 5v output on the feedback circuit.
      • Replace the powertrain control module in accordance with the service information.
        GC0201407Courtesy of CHRYSLER GROUP, LLC
        Blue Channel - Feedback circuit on the FPCM side of the open

BASIC LOAD TESTING OF FPCM POWER AND GROUND CIRCUITS 

  1. Disconnect the FPCM harness connector and load test the FPCM Ground circuit. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to CIRCUIT LOAD TESTING PROCEDURES .
    NOTE:

    A way to verify that there is no resistance in the circuit being tested is to perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.

    1. If the ground circuit fails load testing, repair the FPCM chassis ground.
      GC0174957Courtesy of CHRYSLER GROUP, LLC
    2. If the ground circuit tests good, continue to step 2. 
    NOTE:

    Keep in mind when performing this step that when the ignition is switched on, and the engine is not cranking, the Fuel Pump Relay is energized for approximately 5.0 seconds and then powered down. It will be powered continuously when the engine is cranking or running.

  2. Load test the battery supply to the FPCM harness connector.
    NOTE:

    A way to verify that there is no resistance in the circuit being tested is to perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.

    1. If the battery supply circuit fails load testing, repair the fuel pump relay output circuit for an open or high resistance. If the fuse is open, test the circuit for a short to ground.
    2. If the battery supply circuit checks good, continue to step 3. 
      GC0174938Courtesy of CHRYSLER GROUP, LLC
  3. Reconnect the FPCM harness connector and check the FPCM PWM Feedback circuit. The preferred method is to back probe and check the feedback duty cycle at the FPCM harness connector with a Mopar Scope. Monitor the signal with the engine cranking or running. When the feedback circuit is connected and functioning properly, the scope pattern generated will be a 5v square wave signal. The 5.0 volts is generated in the PCM, with the FPCM controlling the pulse width on the low side.
    1. If the pattern is a constant 5v signal it would indicate that the PCM and feedback circuit are good. The issue is internal to the FPCM control. Replace the FPCM in accordance with the service information.
    2. If the pattern is showing a pulse width signal switching between 1mv and 0.5v it would indicate that the internal FPCM control is active and there is an open feedback circuit or faulty PCM. Isolate and check the feedback circuit for an open. If the feedback circuit checks good, replace the Powertrain Control Module in accordance with the service information.
    3. If the pattern is constant 0v it would indicate a short to ground in the feedback circuit. Test and repair the circuit for a short to ground.
    GC0174938Courtesy of CHRYSLER GROUP, LLC
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