LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Pontiac >> 2007 >> Solstice Base, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 82 (IMA System) >> DTC Troubleshooting >> DTC U1221 (35): Motor Control Module (MCM) Lost Communication with DC-DC Converter
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC U1221 (35): Motor Control Module (MCM) Lost Communication with DC-DC Converter

WARNING: This page is about a different car, the 2011 Honda Insight and 2010 Honda Insight. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
  • Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION  ).
  • If the DTC cannot be cleared, do the troubleshooting for DTC U1204 (55).
  1. Turn the ignition switch to ON (II).
  2. Clear the DTC with the HDS (see DTC CLEAR  ).
  3. Check for Pending or Confirmed DTCs with the HDS.

    Is DTC U1221 (35) indicated? 

    YES  -go to step 4.

    NO  -Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the DC-DC converter and the MCM.

  4. Check the No. 12 IMA (10 A) fuse in the under-dash fuse/relay box.

    Is the fuse OK? 

    YES  -go to step 5.

    NO  -Repair a short to ground in the wire between the DC-DC converter 4P connector and the No. 12 IMA (10 A) fuse. Also replace the No. 12 IMA (10 A) fuse, then go to step  23.

  5. Turn the ignition switch to LOCK (0).
  6. Turn the battery module switch OFF (see DISCONNECTING THE MOTOR POWER CABLE CONNECTOR FROM THE MOTOR STATOR  ).
  7. Remove the IPU cover (see IPU COVER REMOVAL/INSTALLATION  ).
  8. Remove the PCU lid, the PCU busplate, and the PCU cover (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION  ).
  9. Reinstall the PCU busplate (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION ).
  10. Check for poor connection, loose bolts, and damage at the busbars (A).
    Fig 1: Checking For Poor Connections, Loose Bolts, And Damage At The Busbars (A).
    G00500432Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Are the connections OK? 

    YES  -go to step 11.

    NO  -Repair the connections in the busbars, then go to step  23.

  11. Disconnect MCM connector A (31P).
  12. Measure the resistance between MCM connector terminal A25 and body ground.
    Fig 2: Measuring Resistance Between MCM Connector Terminal A25 And Body Ground
    G06429921Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there 1 MΩ or more? 

    YES  -go to step 13.

    NO  -go to step  21.

  13. Disconnect the DC-DC converter 4P connector (A).
    Fig 3: Identifying DC-DC Converter 4P Connector
    G06429922Courtesy of AMERICAN HONDA MOTOR CO., INC.
  14. Turn the ignition switch to ON (II).
  15. Measure the voltage between DC-DC converter 4P connector terminal No. 4 and body ground.
    Fig 4: Measuring Voltage Between DC-DC Converter 4P Connector Terminal 4 And Body Ground
    G00500433Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there battery voltage? 

    YES  -go to step 16.

    NO  -Repair an open in the wire between the DC-DC converter 4P connector and the No. 12 IMA (10 A) fuse, then go to step  23.

  16. Turn the ignition switch to LOCK (0).
  17. Reconnect MCM connector A (31P).
  18. Turn the ignition switch to ON (II).
  19. Measure the voltage between DC-DC converter 4P connector terminal No. 1 and body ground.
    Fig 5: Measuring Voltage Between DC-DC Converter 4P Connector Terminal 1 And Body Ground
    G06429924Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 12 V? 

    YES  -Replace the DC-DC converter (see DC-DC CONVERTER REMOVAL/INSTALLATION  ), then go to step  23.

    NO  -go to step 20.

  20. Measure the voltage between MCM connector terminal A25 and body ground.
    Fig 6: Measuring Voltage Between MCM Connector Terminal A25 And Body Ground
    G06429925Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there about 12 V? 

    YES  -Repair an open in the wire between the DC-DC converter 4P connector and the MCM (A25), then go to step  23.

    NO  -go to step  30.

  21. Disconnect the DC-DC converter 4P connector (A).
    Fig 7: Identifying DC-DC Converter 4P Connector
    G06429926Courtesy of AMERICAN HONDA MOTOR CO., INC.
  22. Measure the resistance between MCM connector terminal A25 and body ground.
    Fig 8: Checking Resistance Between MCM Connector Terminal A25 And Body Ground
    G06429927Courtesy of AMERICAN HONDA MOTOR CO., INC.

    Is there 1 MΩ or more? 

    YES  -Replace the DC-DC converter (see DC-DC CONVERTER REMOVAL/INSTALLATION ), then go to step 23.

    NO  -Repair a short in the wire between the DC-DC converter 4P connector and the MCM (A25), then go to step 23.

  23. Reconnect all connectors.
  24. If removed, reinstall the PCU cover, the PCU busplate, and the PCU lid (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION  ).
  25. If removed, reinstall the IPU cover (see IPU COVER REMOVAL/INSTALLATION  ), then turn the battery module switch ON (see DISCONNECTING THE MOTOR POWER CABLE CONNECTOR FROM THE MOTOR STATOR  ).
  26. Turn the ignition switch to ON (II).
  27. Clear the DTC with the HDS (see DTC CLEAR  ).
  28. Check for Pending or Confirmed DTCs with the HDS.

    Is DTC U1221 (35) Indicated? 

    YES  -Check for poor connections or loose terminals at the MCM and the DC-DC converter, then go to step  1.

    NO  -go to step 29.

  29. 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 28, go to the indicated DTC's troubleshooting.

    NO  -If the screen indicates FAILED, check for poor connections or loose terminals at the MCM and the DC-DC converter, then go to step  1. If the screen indicates NOT COMPLETED, keep the ignition switch ON (II) until a result comes on.

  30. Reconnect all connectors.
  31. Reinstall the PCU cover, the PCU busplate, and the PCU lid (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION  ).
  32. Reinstall the IPU cover (see IPU COVER REMOVAL/INSTALLATION  ), then turn the battery module switch ON (see DISCONNECTING THE MOTOR POWER CABLE CONNECTOR FROM THE MOTOR STATOR  ).
  33. Update the MCM if it does not have the latest software (see MOTOR CONTROL MODULE (MCM) UPDATE  ), or substitute a known-good MCM (see SUBSTITUTING THE MCM  ).
  34. Turn the ignition switch to ON (II).
  35. Check for Pending or Confirmed DTCs with the HDS.

    Is DTC U1221 (35) indicated? 

    YES  -Check for poor connections or loose terminals at the MCM and the DC-DC converter. If the MCM was updated, substitute a known-good MCM (see SUBSTITUTING THE MCM  ), and recheck. If the MCM was substituted, go to step  1.

    NO  -go to step 36.

  36. Monitor the OBD STATUS for DTC U1221 (35) in the DTCs MENU with the HDS.

    Does the screen indicate PASSED? 

    YES  -If the MCM was updated, troubleshooting is complete. If the MCM was substituted, replace the original MCM (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION  ). If any other Pending or Confirmed DTCs were indicated in step 35, go to the indicated DTC's troubleshooting.

    NO  -If the screen indicates FAILED, check for poor connections or loose terminals at the MCM and the DC-DC converter. If the MCM was updated, substitute a known-good MCM (see SUBSTITUTING THE MCM  ), and recheck. If the MCM was substituted, go to step  1. If the screen indicates NOT COMPLETED, keep the ignition switch ON (II) until a result comes on.

scientia non olet · About LEMON Manuals