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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 92 (Engine Controls - Self-Diagnostics - 6.6L Diesel) >> Diagnostic Tests >> DTC U1800: Can Message From The FICM Is Not Received By The ECM >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 2

    IF the engine does not start and the system sets DTC U1800, the fault lies in the FICM or the FICM power and ground circuits.

  2. 3

    If the fault is a short to ground, a short together, or an open between the ECM and the CAN circuit splices, DTC U2104 will also set. These failures effect the entire system.

  3. 4

    If only DTC U1800 and U2106 set, The problem is a short to voltage in the CAN high circuit. This failure does not set DTC U2104.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. IMPORTANT: If DTC U1800 was set during a FRP relay output test with a scan tool, clear the DTC and do not follow this test.
  2. Attempt to start the engine. Does the engine start? If yes, go to next step. If no, go to step  6.
  3. Did DTC U2104 also set? If yes, go to DTC U2104, If no, go to next step.
  4. Did only DTC U1800 and U2106 set? If yes, go to step  10. If no, go to next step.
    1. Observe the Freeze Frame/Failure Records data for this DTC.
    2. Turn OFF the ignition for 30 seconds.
    3. Start the engine.
    4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

    Does the DTC fail this ignition? If yes, go to step  8. If no, go to INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.

  6. Inspect the fuse supplying power to the FICM ignition 1 voltage circuits. Is the fuse open? If yes, go to step  15. If no, go to next step.
    1. Turn ON the ignition with the engine OFF.
    2. Probe the fuse supplying power to the FICM with a test lamp connected the a good ground. Refer to TROUBLESHOOTING WITH A TEST LAMP in Wiring Systems.

    Does the test lamp illuminate? If yes, go to step  13. If no, go to IGNITION (GLOW PLUG) RELAY (6.6L) .

    1. Turn OFF the ignition.
    2. Disconnect the ECM and FICM harness connectors.
    3. Test the CAN high circuit for an open between the CAN harness splice and the FICM. Refer to TESTING FOR CONTINUITY in Wiring Systems.

    Did the resistance measure less than 5Ω? If yes, go to next step. If no, go to step  17.

  9. Test the CAN low circuit for an open between the CAN harness splice and the FICM. Refer to TESTING FOR CONTINUITY in Wiring Systems. Did the resistance measure less than 5Ω? If yes, go to step  16. If no, go to step  18.
    1. Disconnect the ECM, FICM, and TCM if equipped.
    2. Turn ON the ignition, with the engine OFF.
    3. Probe the CAN high circuit at the ECM harness connector with a test lamp connected to a good ground. Refer to TROUBLESHOOTING WITH A TEST LAMP in Wiring Systems.

    Does the test lamp illuminate? If yes, go to step  19. If no, go to next step.

    1. Turn OFF the ignition.
    2. Reconnect the FICM harness connector.
    3. Turn ON the ignition, with the engine OFF.
    4. Probe the CAN high circuit at the ECM harness connector with a test lamp connected to a good ground. Refer to TROUBLESHOOTING WITH A TEST LAMP in Wiring Systems.

    Does the test lamp illuminate? If yes, go to step  20. If no, go to next step.

    12. IMPORTANT: If the vehicle does not have an automatic transmission, answer this step NO.
    1. Turn OFF the ignition.
    2. Reconnect the TCM harness connector.
    3. Turn ON the ignition, with the engine OFF.
    4. Probe the CAN high circuit at the ECM harness connector with a test lamp connected to a good ground. Refer to TROUBLESHOOTING WITH A TEST LAMP in Wiring Systems.

    Does the test lamp illuminate? If yes, go to step  21. If no, go to step  22.

  13. Test the FICM ignition?1 voltage circuits between the fuse and the FICM for an open, and test the entire FICM ignition 1 voltage circuit for high resistance and repair as necessary. Refer to TESTING FOR CONTINUITY and WIRING REPAIRS in Wiring Systems. Did you find and correct the condition? If yes, go to step  23. If no, go to next step.
  14. Test the FICM ground circuits for an open or high resistance and repair as necessary. Refer to TESTING FOR CONTINUITY and WIRING REPAIRS in Wiring Systems. Did you find and correct the condition? If yes, go to step  23. If no, go to step  16.
    1. Disconnect the FICM.
    2. Test the FICM ignition 1 voltage circuits for a short to ground and repair as necessary. Refer to TESTING FOR CONTINUITY and WIRING REPAIRS in Wiring Systems.

    Did you find and correct the condition? If yes, go to step  23. If no, go to step  20.

  16. Test for an intermittent or poor connections at the FICM. Repair as necessary. Refer to TESTING FOR INTERMITTENT & POOR CONNECTIONS and WIRING REPAIRS in Wiring Systems. Did you find and correct the condition? If yes, go to step  23. If no, go to step  20.
  17. Repair the open or high resistance in the CAN high circuit between the FICM and the CAN splice. Refer to WIRING REPAIRS in Wiring Systems. Did you complete the repair? If yes, go to step  23.
  18. Repair the open or high resistance in the CAN low between the FICM and the CAN splice circuit. Refer to WIRING REPAIRS in Wiring Systems. Did you complete the repair? If yes, go to step  23.
  19. Repair the short to voltage in the CAN high circuit. Refer to WIRING REPAIRS in Wiring Systems. Did you complete the repair? If yes, go to step  23.
  20. Replace the FICM. Refer to FUEL INJECTION CONTROL MODULE . Did you complete the replacement? If yes, go to step  23.
  21. Replace the TCM. Refer to TRANSMISSION CONTROL MODULE in Automatic Transmission - Allison. Did you complete the replacement? If yes, go to step  23.
  22. Replace the ECM. Refer to ENGINE CONTROL MODULE . Did you complete the replacement? If yes, go to step  23.
    1. Use a scan tool to clear the DTCs.
    2. Turn OFF the ignition for 30?seconds.
    3. Start the engine.
    4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

    Does the DTC run and pass? If yes, go to next step. If no, go to step  1.

  24. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, go to DTC INDEX . If no, system OK.
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