U1221
DTC U1221 (35): Motor Control Module (MCM) Lost Communication with DC-DC Converter1. Turn the ignition switch ON (II).
2. Reset the MCM.
3. Check for Temporary DTCs or DTCs with the HDS.
Is DTC U1221 indicated?
YES - Go to step 4.
NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the DC-DC converter and the MCM.
4. Check the under-hood fuse/relay box terminal (ORN wire) connection.
Is the connection OK?
YES - Go to step 5.
NO - Repair connection in the wire terminal, then go to step 18.
5. Turn the ignition switch OFF.
6. Turn the battery module switch OFF.
7. Remove the IPU lid.
8. Check the +B connector (A) on the DC-DC converter.
Is +B connector OK?
YES - Go to step 9.
NO - Repair the +B connector (A) on the DC-DC converter as necessary, then go to step 20.
9. Disconnect the DC-DC converter 4P connector.
10. Turn the ignition switch ON (II).
11. Measure voltage between DC-DC converter 4P connector terminal No. 4 and body ground.
Is there battery voltage?
YES - Go to step 12.
NO - Repair open in the wire between the DC-DC converter and the No. 18 ACG (15 A) fuse in the under-dash fuse/relay box, then go to step 20. Replace the No. 18 ACG (15 A) fuse.
12. Turn the ignition switch OFF.
13. Disconnect MCM connector B (24P).
14. Check for continuity between MCM connector terminal B18 and body ground.
Is there continuity?
YES - Repair short in the wire between the DC-DC converter and the MCM (B18), then go to step 20.
NO - Go to step 15.
15. Check for continuity between MCM connector terminal B18 and DC-DC converter 4P connector terminal No. 3.
Is there continuity?
YES - Go to step 16,
NO - Repair open in the wire between the DC-DC converter and the MCM (B18), then go to step 20.
16. Substitute a known-good DC-DC converter.
17. Turn the ignition switch ON (II).
18. Reset the MCM.
19. Check for Temporary DTCs or DTCs with the HDS.
Is DTC U1221 indicated?
YES - Go to step 26.
NO - Replace the original DC-DC converter, then go to step 20.
20. Turn the ignition switch OFF.
21. Reconnect all connectors.
22. Reinstall the IPU lid, then turn the battery module switch ON.
23. Turn the ignition switch ON (II).
24. Reset the MCM.
25. Check for Temporary DTCs or DTCs with the HDS.
Are any Temporary DTCs or DTCs indicated?
YES - If DTC U1221 is indicated, check for poor connections or loose terminals at the DC-DC converter and the MCM, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.
NO - Troubleshooting is complete.
26. Reinstall the IPU lid, then turn the battery module switch ON.
27. Update the MCM if it does not have the latest software, or substitute a known-good MCM.
28. Check for Temporary DTCs or DTCs with the HDS.
Are any Temporary DTCs or DTCs indicated?
YES - If DTC U1221 is indicated, check for poor connections or loose terminals at the DC-DC converter and the MCM, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.
NO - If the MCM was updated, troubleshooting is complete, If the MCM was substituted, replace the original MCM.