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.
2021 Honda Civic TouringFACTORY OEM SERVICE PROCEDURE
Climate Control System
| DTC | Detection Item or Symptom | ECU | DTC Type |
|---|---|---|---|
| B120A | Climate control unit LIN communication bus line error | Climate control unit | Loss of communication |
| B121A | An open in the mode control motor circuit | Climate control unit | Signal error |
| B121B | A short in the mode control motor circuit | Climate control unit | Signal error |
| B1220 | A short in the recirculation control motor circuit | Climate control unit | Signal error |
| B1225 | An open in the in-car temperature sensor circuit | Climate control unit | Signal error |
| B1226 | A short in the in-car temperature sensor circuit | Climate control unit | Signal error |
| B1227 | An open in the outside air temperature sensor circuit | Climate control unit | Signal error |
| B1228 | A short in the outside air temperature sensor circuit | Climate control unit | Signal error |
| B1231*1 | An open in the evaporator temperature sensor circuit | Climate control unit | Signal error |
| B1232*1 | A short in the evaporator temperature sensor circuit | Climate control unit | Signal error |
| B1233 | An open in the air mix control motor circuit (driver's) | Climate control unit | Signal error |
| B1234 | A short in the air mix control motor circuit (driver's) | Climate control unit | Signal error |
| B1235 | A problem in the air mix control motor circuit, linkage, door, or motor (driver's) | Climate control unit | Signal error |
| B1236*2 | An open in the passenger's air mix control motor circuit | Climate control unit | Signal error |
| B1237*2 | A short in the passenger's air mix control motor circuit | Climate control unit | Signal error |
| B1238*2 | A problem in the passenger's air mix control motor circuit, linkage, door, or motor | Climate control unit | Signal error |
| B123F | Automatic lighting control unit/sunlight sensor error | Climate control unit | Signal error |
| B1240 | A problem in the mode control motor circuit, linkage, door, or motor | Climate control unit | Signal error |
| B1241 | A problem in the blower motor circuit | Climate control unit | Signal error |
| B2964 | Climate control unit lost communication with front panel (climate control panel) | Climate control unit | Loss of communication |
| B2983 | A problem in the recirculation control motor circuit, linkage, door, or motor | Climate control unit | Signal error |
| B2986 | An open in the recirculation control motor circuit | Climate control unit | Signal error |
| B2988*1 | A problem in the A/C compressor variable capacity control solenoid circuit | Climate control unit | Signal error |
| U1280 | Communication bus line error (BUS-OFF) | Climate control unit | Loss of communication |
| U1281 | Climate control unit lost communication with MICU (body control module) | Climate control unit | Loss of communication |
| U128D | Climate control unit lost communication with gauge control module | Climate control unit | Loss of communication |
| U1290*3 | Climate control unit lost communication with seat heater control unit (front) | Climate control unit | Loss of communication |
*1: With A/C
*2: With dual zone climate control
*3: With seat heater
Factory Service Tools
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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.