DTC B1843: UART Communication Error

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).
Operate the power seat with the driving position memory switch.
Check for DTCs with the HDS.
Is DTC B1843 indicated?

YES -Go to step 5.

NO -Intermittent failure, the system is OK at this time. Check for loose or poor connections.
Turn the ignition switch to LOCK (0).
Disconnect the power seat control unit connectors and power mirror control unit 24P connector.
Check for continuity between power seat control unit connector B (40P) terminal No. 38 and power mirror control unit 24P connector terminal No. 13.

Fig 1: Checking Continuity Between Power Seat Control Unit Connector B (40P) Terminal No. 38 And Power Mirror Control Unit 24P Connector Terminal No. 13
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Go to step 8.

NO -Repair an open in the wire between the power mirror control unit and power seat control unit.
Check for continuity between power seat control unit connector B (40P) terminal No. 38 and body ground.

Fig 2: Checking Continuity Between Power Seat Control Unit Connector B (40P) Terminal No. 38 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES -Repair a short to ground in the UART wire.

NO -Go to step 9.
Reconnect the power mirror control unit 24P connector.
Turn the ignition switch to ON (II).
Measure the voltage between body ground and power mirror control unit 24P connector terminal No. 24.

Fig 3: Measuring Voltage Between Body Ground And Power Mirror Control Unit 24P Connector Terminal No. 24
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?

YES -Go to step 12.

NO -Check the No. 23 (10 A) fuse in the under-hood fuse/relay box. If the fuse is OK, repair an open or high resistance in the wire.
Measure the voltage between power mirror control unit 24P connector terminal No. 22 and body ground.

Fig 4: Measuring Voltage Between Power Mirror Control Unit 24P Connector Terminal No. 22 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 0.2 V or more?

YES -Repair an open or high resistance in the wire between the power mirror control unit and body ground (G401). If the wire is OK, repair G401.

NO -Replace the power mirror control unit (see POWER MIRROR CONTROL UNIT INPUT TEST/REPLACEMENT ).