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

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.

Turn the ignition switch to ON (II).
Clear the DTC with the HDS (see DTC CLEAR ).
Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 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.
Check the No. B12 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. B12 IMA (10 A) fuse. Also replace the No. B12 IMA (10 A) fuse, then go to step 23.
Turn the ignition switch to LOCK (0).
Turn the battery module switch OFF (see TURNING OFF AND ON POWER TO THE HIGH VOLTAGE CIRCUIT ).
Remove the IPU cover (see IPU COVER REMOVAL/INSTALLATION ).
Remove the PCU lid, the PCU busplate, and the PCU cover (see IPU CASE REMOVAL/INSTALLATION ).
Reinstall the PCU busplate (see IPU CASE REMOVAL/INSTALLATION ).
Check for poor connections, loose bolts, and damage at the busbars (A).

Fig 1: Busbars With Bolts With Torque Specifications
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Are the busbar connections OK?

YES -Go to step 11.

NO -Repair the busbar connections, then go to step 23.
Disconnect MCM connector A (31P).
Measure the resistance between MCM connector terminal A28 and body ground.

Fig 2: Measuring Resistance Between MCM Connector Terminal A28 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 1 MΩ or more?

YES -Go to step 13.

NO -Go to step 21.
Disconnect the DC-DC converter 4P connector (A).

Fig 3: Identifying DC-DC Converter 4P Connector Component Location
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Turn the ignition switch to ON (II).
Measure the voltage between DC-DC converter 4P connector terminal No. 1 and body ground.

Fig 4: Measuring Voltage Between DC-DC Converter 4P Connector Terminal No. 1 And Body Ground
Courtesy 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. B12 IMA(10A) fuse, then go to step 23.
Turn the ignition switch to LOCK (0).
Reconnect MCM connector A (31P).
Turn the ignition switch to ON (II).
Measure the voltage between DC-DC converter 4P connector terminal No. 4 and body ground.

Fig 5: Measuring Voltage Between DC-DC Converter 4P Connector Terminal No. 4 And Body Ground
Courtesy 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.
Measure the voltage between MCM connector terminal A28 and body ground.

Fig 6: Measuring Voltage Between MCM Connector Terminal A28 And Body Ground
Courtesy 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 (A28), then go to step 23.

NO -Go to step 29.
Disconnect the DC-DC converter 4P connector (A).

Fig 7: Identifying DC-DC Converter 4P Connector Component Location
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Measure the resistance between MCM connector terminal A28 and body ground.

Fig 8: Measuring Resistance Between MCM Connector Terminal A28 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 1MΩ 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 (A28), then go to step 23.
Reconnect all connectors.
Reinstall the PCU cover, the PCU busplate, and the PCU lid (see IPU CASE REMOVAL/INSTALLATION ).
Reinstall the IPU cover (see IPU COVER REMOVAL/INSTALLATION ), then turn the battery module switch ON (see TURNING OFF AND ON POWER TO THE HIGH VOLTAGE CIRCUIT ).
Turn the ignition switch to ON (II).
Clear the DTC with the HDS (see DTC CLEAR ).
Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 indicated?

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

NO -Troubleshooting is complete. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC'S TROUBLESHOOTING .
Reconnect all connectors.
Reinstall the PCU cover, the PCU busplate, and the PCU lid (see IPU CASE REMOVAL/INSTALLATION ).
Reinstall the IPU cover (see IPU COVER REMOVAL/INSTALLATION ), then turn the battery module switch ON (see TURNING OFF AND ON POWER TO THE HIGH VOLTAGE CIRCUIT ).
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 ).
Turn the ignition switch to ON (II).
Check for Pending or Confirmed DTCs with the HDS.
Is DTC U1221 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 ), then recheck. If the MCM was substituted, go to step 1.

NO -If the MCM was updated, troubleshooting is complete. If the MCM was substituted, replace the original MCM (see IPU CASE REMOVAL/INSTALLATION ). If any other Pending or Confirmed DTCs were indicated, go to the indicated DTC'S TROUBLESHOOTING .