DTC B1843: Power Seat Control Unit Lost Communication With Other Units (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 DTC with the HDS.
Turn the ignition switch OFF, and then back ON (II).
Operate the power seat with the driving position memory switch.
Check for DTCs with the HDS.
Is DTC 1843 indicated?
1. YES - Go to step 5.
2. NO - Intermittent failure, the system is OK at this time.
Turn the ignition switch OFF.
Disconnect the power seat control unit connectors and power mirror control unit connector (26P).
Check for continuity between the power seat control unit connector C (12P) No. 4 terminal and power mirror control unit connector (26P) No. 23 terminal.

Fig 1: Checking Continuity Between Power Seat Control Unit Connector C (12P) No. 4 Terminal & Power Mirror Control Unit Connector (26P) No. 23
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Go to step 8.
2. NO - Repair an open in the PUR wire between the power mirror control unit connector (26P) and the power seat control unit connector C (12P).
Check for continuity between the power seat control unit connector C (12P) No. 4 terminal and body ground with the ignition switch ON (II).

Fig 2: Checking Continuity Between Power Seat Control Unit Connector C (12P) No. 4 Terminal & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Repair a short in the PUR wire to ground.
2. NO - Go to step 9.
Measure the voltage between the No. 13 terminal of the power mirror control unit connector (26P) and body ground.

Fig 3: Measuring Voltage Between No 13 Terminal Of Power Mirror Control Unit Connector (26P) & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?
1. YES - Go to step 10.
2. NO - Check No. 7 (7.5 A) fuse in the under-dash fuse/relay box. If the fuse is OK, repair an open in the WHT/RED wire.
Check for continuity between the No. 25 terminal of power mirror control unit connector (26P) and body ground.

Fig 4: Checking Continuity Between No 25 Terminal Of Power Mirror Control Unit Connector (26P) & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES - Repair an open in the wire between the power mirror control unit and G501. If the wire is OK, repair G501.
2. NO - Replace the power mirror control unit.