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.
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HOMESERVICE MANUALSHONDA2020CIVIC SI, 4D SEDANREPAIR AND DIAGNOSIS (SINGLE PAGE)QUICK LOOKUPSDTC INDEXCLIMATE CONTROL DTCSCLIMATE CONTROL SYSTEM
2020 Honda Civic Si, 4D Sedan
Climate Control System
2020 Honda Civic Si, 4D SedanSECTION 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
RENDER: 1.0x
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.