B1231 The climate control unit saw an open in the evaporator temperature sensor circuit
What does B1231 mean on a Honda?
B1231. The climate control unit saw an open in the evaporator temperature sensor circuit. The A/C may cycle wrong and the evaporator can freeze up. This Honda-enhanced code applies to Honda and Acura models that use this code.
Common causes of B1231
- Faulty evaporator temperature sensor
- Open in the evaporator temperature sensor circuit
- Poor electrical connection at the evaporator sensor connector
- Faulty climate control unit
- Corroded or loose connector pins at the sensor
How to fix B1231
- Confirm the code and check the climate control for related faults
- Inspect the sensor connector for corrosion, moisture, and loose pins
- Test the sensor signal and reference voltage at the connector
- Check the wiring for an open before replacing the sensor
- Replace the evaporator temperature sensor if it fails testing
- Clear the code and retest
Sources and review
- Last updated 2026-10-10.