DTC U1291: MICU Lost Communication With Relay Control Module (RM Frame)

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NOTE: If you are troubleshooting multiple DTCs, be sure to follow the instructions in B-CAN System Diagnosis Test Mode A (see TROUBLESHOOTING - B-CAN SYSTEM DIAGNOSIS TEST MODE A ).

Clear the DTCs with the HDS.
Turn the ignition switch to LOCK (0), and then back to ON (II).
Wait for at least 6 seconds.
Check for DTCs with the HDS.
Is DTC U1291 indicated?

YES -Go to step 5.

NO -Intermittent failure, the system is OK at this time. Check for loose or poor connections between the MICU and the relay control module.
Measure the voltage between body ground and relay control module connector B (16P) terminals No. 9 and No. 10 individually.

Fig 1: Measuring Voltage Between Body Ground And Relay Control Module Connector B (16P) Terminals No. 9 And No. 10
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?

YES -Go to step 8.

NO -Go to step 6.
Turn the ignition switch to LOCK (0).
Check the No. B16 (10 A) and the No. B6 (7.5 A) fuses in the under-hood fuse/relay box.
Are the fuses OK?

YES -Repair an open or high resistance in the No. B16 (10 A) and/or No. B6 (7.5 A) fuse circuit.

NO -Replace the fuse(s). If the fuse blows again, repair a short to ground in the No. B16 (10 A) and/or No. B6 (7.5 A) fuse circuit.
Measure the voltage between body ground and relay control module connector B (16P) terminal No. 1.

Fig 2: Measuring Voltage Between Body Ground And Relay Control Module Connector B (16P) Terminal No. 1
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there less than 0.2 V?

YES -Go to step 9.

NO -Repair an open or high resistance in the ground wire or poor ground (G203).
Measure the voltage between body ground and relay control module connector D (14P) terminal No. 12.

Fig 3: Measuring Voltage Between Body Ground And Relay Control Module Connector D (14P) Terminal No. 12
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there less than 0.2 V?

YES -Go to step 10.

NO -Repair an open or high resistance in the ground wire or poor ground (G203).
Turn the ignition switch to LOCK (0).
Disconnect driver's under-dash fuse/relay box connector H(13P).
Disconnect relay control module connector B (16P).
Check for continuity between driver's under-dash fuse/relay box connector H (13P) terminals No. 5 and No. 10 and relay control module connector B (16P) terminals No. 15 and No. 16 respectively.

Fig 4: Checking Continuity Between Driver's Under-Dash Fuse/Relay Box Connector H (13P) Terminals No. 5 And No. 10
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Replace the relay control module (see REMOVAL AND INSTALLATION ).

NO -An open or poor connection in the B-CAN wire between the relay control module and the MICU.