DTC U1153: Loss Of Communication With HVAC: Testing

If IPC diagnostic system check was performed, go to next step. If IPC diagnostic system check was not performed, go to procedures in IPC DIAGNOSTIC SYSTEM CHECK .
Turn ignition off. Connect scan tool. Turn ignition on. Using scan tool, attempt to establish communication with HVAC system. If communication can be established, go to next step. If communication cannot be established, check serial data line. See WIRING DIAGRAMS . If serial data line is okay, locate and repair problem in HVAC system. See procedures in A/C-HEATER SYSTEM article in AIR CONDITIONING & HEAT section
Using scan tool, select IPC DTCs function. Check for DTC U1255. If DTC U1255 exists, go to DTC U1255: SERIAL DATA LINE MALFUNCTION . If DTC U1255 does not exist, go to next step.
Check serial data line for following intermittent conditions:
- An open in serial data line between IPC and HVAC system.
- 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 6).
Turn ignition off. Reinstall all components and connectors. Turn ignition on. Clear DTCs. Check for DTCs. If DTC U1153 is current, check serial data line. See WIRING DIAGRAMS . If serial data line is okay, locate and repair problem in HVAC system. See procedures in A/C-HEATER SYSTEM article in AIR CONDITIONING & HEAT section. If DTC U1153 is not current, system is operating properly.
Turn ignition off. Reinstall all components and reconnect all connectors. Turn ignition on. Clear DTCs. Perform procedures in IPC DIAGNOSTIC SYSTEM CHECK .