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 Clarity Plug-In HybridFACTORY OEM SERVICE PROCEDURE
HVAC System DTCS
DTC B120A - B1241
| DTC | Detection Item or Symptom | ECU | DTC Type |
|---|---|---|---|
| B120A | Climate Control Unit LIN Communication Bus Line Error | Climate control unit | Loss of communication |
| B1211 | An Open in the ECOMP Circuit | Climate control unit | Signal error |
| B1212 | An Open in the HVHTR Circuit | Climate control unit | Signal error |
| 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 |
| B121D | Humidity/in-car temperature sensor communication error | Climate control unit | Loss of communication |
| B1220 | A Short in the recirculation control motor circuit | Climate control unit | Signal error |
| B1231 | An open in the evaporator temperature sensor circuit | Climate control unit | Signal error |
| B1232 | 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 | An open in the passenger's air mix control motor circuit | Climate control unit | Signal error |
| B1237 | A short in the passenger's air mix control motor circuit | Climate control unit | Signal error |
| B1238 | 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 |
DTC B2964 - B2998
| DTC | Detection Item or Symptom | ECU | DTC Type |
|---|---|---|---|
| B2964 | Climate control unit lost communication with Front PANEL | Climate control unit | Loss of communication |
| B296D | Electric Heater Coolant Pump Communication Fail | Climate control unit | Loss of communication |
| B296E | Electric Heater Coolant Pump Fail | Climate control unit | Signal error |
| B296F | Electric Water Valve Fail | Climate control unit | Signal error |
| 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 |
| B298A | Electric Coolant Heater fail | Climate control unit | Signal error |
| B298B | A/C Main Relay ON Fail | Climate control unit | Signal error |
| B2990 | A problem in the A/C compressor driving circuit | Climate control unit | Signal error |
| B2996 | An open in the heater core temperature sensor circuit | Climate control unit | Signal error |
| B2997 | A short in the heater core temperature sensor circuit | Climate control unit | Signal error |
| B2998 | A problem in the A/C compressor driver | Climate control unit | Signal error |
DTC U0029 - U124A
| DTC | Detection Item or Symptom | ECU | DTC Type |
|---|---|---|---|
| U0029 | F-CAN communication line error | Climate control unit | Loss of communication |
| U0100 | Climate Control Unit Lost Communication With MG Module | Climate control unit | Loss of communication |
| U0180 | Climate Control Unit Lost communication with automatic lighting control unit-sensor | Climate control unit | Loss of communication |
| U1207 | Climate Control Unit Lost Communication With ECOMP Module | Climate control unit | Loss of communication |
| U1280 | Communication bus line error (BUS-OFF) | Climate control unit | Loss of communication |
| U1281 | Climate Control Unit Lost Communication with MICU | Climate control unit | Loss of communication |
| U128D | Climate Control Unit Lost communication with gauge control module | Climate control unit | Loss of communication |
| U1290 | Climate Control Unit Lost Communication With Seat Heater Control Unit | Climate control unit | Loss of communication |
| U12A4 | Climate Control Unit Lost Communication With HVHTR Module | Climate control unit | Loss of communication |
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.
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