DTC Troubleshooting
DTC Troubleshooting: U1221 (35)
DTC U1221 (35):
BCM Module Lost Communication with DC-DC Converter
NOTE: Before you troubleshoot, record all freeze data, and review the general troubleshooting information Initial Inspection and Diagnostic Overview.
1. Turn the ignition switch to ON (II).
2. Monitor the OBD STATUS for DTC U1221 (35) in the DTCs MENU with the HDS.
Does the screen indicate FAILED?
YES -
Go to step 3.
NO -
If the screen indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the DC-DC converter and the BCM module. If the screen indicates NOT COMPLETED, go to step 1 and recheck.
3. Turn the ignition switch to LOCK (0).
4. Turn the battery module switch OFF High Voltage Safety.
5. Remove the IPU lid IPU Lid Removal/Installation.
6. Check the DC-DC converter terminal (ORN wire) (A) connection.
Is the connection OK?
YES -
Go to step 7.
NO -
Repair the connection, then go to step 21.
7. Disconnect the DC-DC converter 4P connector.
8. Turn the ignition switch to ON (II).
9. Measure the voltage between DC-DC converter 4P connector terminal No. 2 and body ground.
Is there battery voltage?
YES -
Go to step 10.
NO -
- Repair open in the wire between the DC-DC converter and the No. 3 ALTERNATOR (10 A) fuse in the under-dash fuse/relay box, then go to step 20.
- Check the No. 3 ALTERNATOR (10 A) fuse. If needed, replace it, then go to step 20.
10. Turn the ignition switch to LOCK (0).
11. Disconnect BCM module connector A (40P).
12. Check for continuity between BCM module connector terminal A18 and body ground.
Is there continuity?
YES -
Repair short to ground in the wire between the BCM module (A18) and the DC-DC converter, then go to step 21.
NO -
Go to step 13.
13. Check for continuity between BCM module connector terminal A18 and DC-DC converter 4P connector terminal No. 4.
Is there continuity?
YES -
Go to step 14.
NO -
Repair open in the wire between the BCM module (A18) and the DC-DC converter, then go to step 21.
14. Substitute a known-good DC-DC converter Service and Repair.
15. Reconnect all connectors.
16. Reinstall the IPU lid IPU Lid Removal/Installation, then turn the battery module switch ON High Voltage Safety.
17. Turn the ignition switch to ON (II).
18. Clear the DTC with the HDS Initial Inspection and Diagnostic Overview.
19. Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 (35) indicated?
YES -
Go to step 27.
NO -
Replace the original DC-DC converter Service and Repair, then go to step 20.
20. Turn the ignition switch to LOCK (0).
21. Reconnect all connectors.
22. Reinstall the IPU lid IPU Lid Removal/Installation, then turn the battery module switch ON High Voltage Safety.
23. Turn the ignition switch to ON (II).
24. Clear the DTC with the HDS Initial Inspection and Diagnostic Overview.
25. Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 (35) indicated?
YES -
Check for poor connections or loose terminals at the DC-DC converter and the BCM module, then go to step 1.
NO -
Go to step 26.
26. Monitor the OBD STATUS for DTC U1221 (35) in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES -
Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated in step 25, go to the indicated DTC's troubleshooting.�
NO -
If the screen indicates FAILED, check for poor connections or loose terminals at the DC-DC converter and the BCM module, then go to step 1. If the screen indicates NOT COMPLETED, keep the ignition switch ON (II) until a result comes on.
27. Reconnect all connectors.
28. Reinstall the IPU lid IPU Lid Removal/Installation, then turn the battery module switch ON High Voltage Safety.
29. Update the BCM module if it does not have the latest software Testing and Inspection, or substitute a known-good BCM module Initial Inspection and Diagnostic Overview.
30. Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 (35) indicated?
YES -
Check for poor connections or loose terminals at the DC-DC converter and the BCM module. If the BCM module was updated, substitute a known-good BCM module Initial Inspection and Diagnostic Overview, then recheck. If the BCM module was substituted, go to step 1.�
NO -
Go to step 31.
31. Monitor the OBD STATUS for DTC U1221 (35) in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES -
If the BCM module was updated, troubleshooting is complete. If the BCM module was substituted, replace the original BCM module Service and Repair. If any other Pending or Confirmed DTCs were indicated in step 30, go to the indicated DTC's troubleshooting.�
NO -
If the screen indicates FAILED, check for poor connections or loose terminals at the DC-DC converter and the BCM module. If the BCM module was updated, substitute a known-good BCM module Initial Inspection and Diagnostic Overview, then recheck. If the BCM module was substituted, go to step 1. If the screen indicates NOT COMPLETED, keep the ignition switch ON (II) until a result comes on.