Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC B1843: UART Communication Error
- Clear the DTCs with the HDS.
- Turn the ignition switch to LOCK (0) and then back to ON (II).
- Check for DTCs with the HDS.
Is DTC B1843 indicated?
YES -Go to step 4.
NO -Intermittent failure, the system is OK at this time. Check for loose or poor connections.
- Move the power mirrors in each direction with the power mirrors switch.
Do the power mirrors move in each direction smoothly?
YES -Go to step 5.
NO -Go to step 10.
- Turn the ignition switch to LOCK (0).
- Disconnect power seat control unit connector A (40P).
- Disconnect the power mirror control unit 24P connector.
- Check for continuity between power seat control unit connector A (40P) terminal No. 39 and power mirror control unit connector (24P) terminal No. 13 respectively.Fig 1: Checking Continuity Between Power Seat Control Unit Connector A (40P) Terminal 39 And Mirror Control Unit Connector (24P) Terminal 13
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there continuity?
YES -Go to step 9.
NO -Repair open or high resistance 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 short to ground in the wire.
NO -Substitute a known-good power mirror control unit and recheck. If DTC B1843 is still indicated, replace the power seat control unit (see POWER SEAT CONTROL UNIT INPUT TEST/REPLACEMENT ).
- Turn the ignition switch to LOCK (0).
- Disconnect the power mirror control unit 24P connector.
- Turn the ignition switch to ON (II).
- Measure the voltage between the power mirror control unit 24P connector terminals No. 11 and No. 22 and between terminals No. 24 and No. 22 respectively.Fig 3: Measuring Voltage Between Power Mirror Control Unit 24P Connector Terminals 11 And Between Terminals 24
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Is there battery voltage?
YES -Replace the power mirror control unit.
NO -Repair an open or high resistance in the wire.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.