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DTC U1255: Serial Data Line Malfunction: Testing

  1. If BCM diagnostic system check was performed, go to next step. If BCM diagnostic system check was not performed, see procedures in BCM DIAGNOSTIC SYSTEM CHECK  .
  2. Turn ignition off. Install scan tool. Turn ignition on. Using scan tool, attempt to establish communication with PCM. If communication can be established, go to next step. If communication cannot be established, see TESTS W/CODES article in ENGINE PERFORMANCE section.
  3. Using scan tool, attempt to establish communication with IPC. If communication can be established, go to next step. If communication cannot be established, see INSTRUMENT PANEL article.
  4. Check serial data line for following intermittent conditions:
    • An open in serial data line between BCM and PCM or IPC.
    • Short to ground.
    • Short to voltage.
    • Check star connector No. 1 (ensure bus bar is properly inserted).
    • Loose or damaged terminals.

    If no problem is found, go to next step. If problem is found, repair as necessary. Go to step 7).

  5. Turn ignition off. Reinstall all components and connectors. Turn ignition on. Clear DTCs. Check for DTCs. If DTC U1255 is current, go to next step. If DTC U1255 is not current, system is operating properly.
  6. Replace BCM. See REMOVAL & INSTALLATION  . Reprogram BCM. See BCM PROGRAMMING/RPO CONFIGURATION  . Go to next step.
  7. Turn ignition off. Reinstall all components and connectors. Turn ignition on. Clear DTCs. Perform BCM DIAGNOSTIC SYSTEM CHECK  .
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