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Home >> Ford >> 2003 >> Excursion 6.0 P, RWD >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 6.0L (99P F450/550) Diesel >> System Tests >> Test AF: Glow Plug System >> Testing
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Test AF: Glow Plug System: Testing

CAUTION: When disconnecting Green and Black connectors at GPCM it is suggested that GPCM be unbolted from mounting bracket first and then connectors disconnected. This will allow for easier disconnect and will help prevent damage to connector terminals.
NOTE: Make sure that the vehicle batteries are fully charged prior to carrying out the glow plug diagnostic tests. The glow plug diagnostic test requires a scan tool.

  1. 1) DTCs P0670, P0671-P0678 & P0683

    Possible causes are:
    • Faulty glow plug bus bar harness.
    • Open glow plug circuit.
    • Damaged connector.
    • Shorted glow plug circuit.
    • Faulty GPCM.
    • Failed glow plug.

    Perform the KOEO ON-DEMAND SELF-TEST  and RETRIEVE/CLEAR CONTINUOUS MEMORY DTCS  under QUICK TEST. Is one or more of the following DTCs present: DTC P0670, DTC P0671, DTC P0672, DTC P0673, DTC P0674, DTC P0675, DTC P0676, DTC P0677, DTC P0678 or DTC P0683? If yes, for DTC P0670, go to step  7). For DTC P0683, go to step  13). For all others, go to next step. If no, unable to duplicate condition. Check for loose connections, damaged or corroded terminals or pins. Wiggle harness attempting to recreate the fault. Repair as necessary. See TROUBLE SHOOTING - NO CODES - DIESEL - 6.0L article if a driveability concern exists.

    2. NOTE: Glow plugs are numbered front to rear with even numbers on left side of engine.

  2. 2) Check Glow Plug Circuit For A Short To Voltage
    Use wiring diagram to match connector pins with DTCs. See WIRING DIAGRAMS . Disconnect faulted GPCM harness connector. Disconnect faulted glow plug bus bar connector. See GLOW PLUG DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table. Check for loose, damaged or backed out terminals. Key on. Measure the voltage between faulted GPCM harness connector pins and ground. See Figure. Are any voltage values greater than 0.2 volts? (Typical resistance value of a good glow plug and wiring is 1 ohm.) If yes, repair short to voltage in faulted circuit. Restore the vehicle. Clear DTCs and retest the system. If no, go to next step.
    GLOW PLUG DIAGNOSTIC TROUBLE CODE IDENTIFICATION

    DTC Glow Plug No.
    P0671 1
    P0672 2
    P0673 3
    P0674 4
    P0675 5
    P0676 6
    P0677 7
    P0678 8

  3. 3) Check Glow Plug Circuit For A Short To Ground

    Key off. Measure the resistance between faulted GPCM harness connector pins and ground. Are all resistance values greater than 10,000 ohms? If yes, go to next step. If no, repair short to ground in faulted circuit. Restore the vehicle. Clear DTCs and retest the system.

  4. 4) Check Glow Plug Circuit For An Open

    Measure the resistance between faulted GPCM harness connector pins and bus bar harness connector pins. See WIRING DIAGRAMS  to match pins between GPCM and bus bar connectors. Are all the resistance values less than 0.5 ohm? If yes, go to next step. If no, repair open in faulted circuit. Restore the vehicle. Clear DTCs and retest the system.

  5. 5) Check Glow Plug Circuit Between Bus Bar Connector & Glow Plug

    Measure the resistance between faulted bus bar harness connector pins and ground. See WIRING DIAGRAMS  to match pins between GPCM and bus bar connectors. Are all resistance values 0.5-1.0 ohm? If yes, install a new GPCM. Restore the vehicle. Clear DTCs and retest the system. If no, go to next step.

  6. 6) Check Glow Plug Circuit Between Bus Bar Connector & Glow Plug

    Disconnect the bus bar harness from glow plugs. Measure the resistance between faulted bus bar harness connector pins and glow plug connector pins. See WIRING DIAGRAMS  to match pins between GPCM and bus bar connectors. Are all resistance values less than 0.5 ohm? If yes, install new glow plug for a faulted circuit. Restore the vehicle. Clear DTCs and retest the system. If no, install a new bus bar connector. Restore the vehicle. Clear DTCs and retest the system.

  7. 7) DTC P0670

    Possible causes are:
    • Open control line.
    • Control line shorted to ground or power.
    • Faulty PCM circuit.
    • Faulty GPCM circuit.

    Perform the KOEO ON-DEMAND SELF-TEST  and RETRIEVE/CLEAR CONTINUOUS MEMORY DTCS  under QUICK TEST. Is DTC P0670 present? If yes, go to next step. If no, check for loose connections. Check pins for damage or corrosion. Wiggle the wiring harness while taking measurements. Restore the vehicle. Clear DTCs and retest the system.

  8. 8) Check Control Circuit For A Short To Voltage

    Key off. Disconnect the PCM engine connector C1381C. Disconnect the GPCM (Green) connector. Key on. Measure the voltage between GPCM Green harness connector terminal No. 8 and ground. See Figure. Is the voltage less than 0.2 volt? If yes, go to next step. If no, repair short to voltage in GPCM control circuit. Restore the vehicle. Clear DTCs and retest the system.

  9. 9) Check Control Circuit For A Short To Ground

    Key off. Measure the resistance between the GPCM Green harness connector terminal No. 8 and ground. Is the resistance greater than 10,000 ohms? If yes, go to next step. If no, repair short in GPCM control circuit. Restore the vehicle. Clear DTCs and retest the system.

  10. 10) Check Control Circuit For An Open

    Measure the resistance between the GPCM Green harness connector terminal No. 8 and the PCM engine harness connector C1381C terminal No. 3. See CONTROL MODULE CONNECTOR IDENTIFICATION . Is the resistance less than 5 ohms? If yes, go to next step. If no, repair open in GPCM control circuit. Restore the vehicle. Clear DTCs and retest the system.

  11. 11) Check GPCM Circuit

    Reconnect the GPCM Green harness connector. Key on. Measure the voltage between PCM engine harness connector C1381C terminal No. 3 and ground. Is the voltage above 10 volts? If yes, replace the PCM. Restore the vehicle. Clear DTCs and retest the system. If no, go to next step.

  12. 12) Check For GPCM System Operating Voltage

    Key off. Disconnect the GPCM (Green) and (Black) harness connectors. Key on. Measure the voltage between GPCM Black connector terminals No. 3 and 9, and ground; and between the Green connector terminal No. 3 and ground. Are voltage measurements above 10 volts? If yes, replace the GPCM. Restore the vehicle. Clear DTCs and retest the system. If no, repair open in system operating circuit. Restore the vehicle. Clear DTCs and retest the system.

  13. 13) DTC P0683

    Possible causes are:
    • Open diagnostic line.
    • Diagnostic line shorted to ground or power.
    • Faulty PCM circuit.
    • Faulty GPCM circuit.

    Perform the KOEO ON-DEMAND SELF-TEST  and RETRIEVE/CLEAR CONTINUOUS MEMORY DTCS  under QUICK TEST. Is DTC P0683 present? If yes, clear DTCs and retest, make sure DTC P0670 is not present. If DTC P0670 is present, carry out DTC P0670 test sequence (go to step  7), and fix problem before carrying out DTC P0683 tests. Go to next step. If no, unable to duplicate condition. Check for loose connections, damaged or corroded pins. Wiggle harness attempting to recreate fault.

  14. 14) Check Diagnostic Circuit For A Short To Voltage

    Key off. Disconnect the PCM engine harness connector C1381C. Disconnect the GPCM (Green) connector. Key on. Measure the voltage between GPCM Green connector terminal No. 9 and ground. See Figure. Is the voltage less than 0.2 volt? If yes, go to next step. If no, repair short to voltage in diagnostic circuit. Restore the vehicle. Clear DTCs and retest the system.

  15. 15) Check Diagnostic Circuit For A Short To Ground

    Key off. Measure the resistance between GPCM Green harness connector terminal No. 9 and ground. Is the resistance greater than 10,000 ohms? If yes, go to next step. If no, repair short in GPCM diagnostic circuit. Restore the vehicle. Clear DTCs and retest the system.

  16. 16) Check Diagnostic Circuit For An Open

    Measure the resistance between the GPCM Green harness connector terminal No. 9 and PCM engine harness connector C1381C terminal No. 17. See CONTROL MODULE CONNECTOR IDENTIFICATION . Is the resistance less than 5 ohms? If yes, go to next step. If no, repair open in diagnostic circuit. Restore the vehicle. Clear DTCs and retest the system.

  17. 17) Check GPCM Function

    Reconnect the GPCM electrical connectors. Disconnect the engine oil temperature sensor (this will maximize the glow "on" time). Engine oil temperature sensor is located on top of engine between alternator and turbocharger. Install a voltmeter between PCM engine harness connector C1381C terminal No. 17 and ground. Install a jumper wire between PCM engine harness connector C1381C terminal No. 3 and ground. Key on. Is the voltage between 5 and 12 volts? If yes, install a new PCM. Restore the vehicle. Clear DTCs and retest the system. If no, install a new GPCM. Restore the vehicle. Clear DTCs and retest the system.
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