DTC B1843: Power Seat Control Unit Lost Communication with Power Tilt/Telescopic Steering Control Unit (UART Line)

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 OFF, and then back ON (II).
Check for DTCs with the HDS.
Is DTC B1843 indicated?

YES - Go to step 4.

NO - Intermittent failure, the communication system is OK at this time. Check for loose or poor connections at the power seat control unit.
Move the tilt/telescopic steering in each direction with the tilt/telescopic switch.
Does the tilt/telescopic steering move in each direction smoothly?

YES - Go to step 5.

NO - Go to step 10.
Turn the ignition switch OFF.
Disconnect power seat control unit connector A (40P).
Disconnect power tilt/telescopic control unit connector A (16P).
Check for continuity between power seat control unit connector A (40P) terminal No. 39 and power tilt/telescopic control unit connector A (16P) terminal No. 11.

Fig 1: Checking Continuity Between Terminal No. 39 And Terminal No. 11
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Go to step 9.

NO - Repair an open in the wire.
Check for continuity between power seat control unit connector A (40P) terminal No. 39 and body ground.

Fig 2: Checking Continuity Between Power Seat Control Unit Connector A (40P) Terminal No. 39 And Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?

YES - Repair a short to ground in the wire.

NO - Substitute a known-good power tilt/telescopic control unit and recheck. If DTC B1843 is still indicated, replace the power seat control unit.
Turn the ignition switch OFF.
Disconnect power tilt/telescopic steering control unit connectors A (16P) and B (8P).
Turn the ignition switch ON (II).
Measure the voltage between power tilt/telescopic steering control unit connector A (16P) terminal No. 9 and connector B (8P) terminal No. 1, and between connector A (16P) terminal No. 1 and connector B (8P) terminal No. 1.

Fig 3: Measuring Voltage Between Terminal No. 9 And Terminal No. 1
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?

YES - Replace the power tilt/telescopic steering control unit.

NO - Do the power tilt/telescopic steering control unit input test (see POWER TILT/TELESCOPIC STEERING CONTROL UNIT INPUT TEST ).