B0300HVAC Evaporator Temperature Sensor Circuit
- Generic OBD-II code · Body
- How the car detects it
- Public code lists do not show B0300, and factory documentation for it is missing too. The evaporator temperature sensor is a thermistor on or just behind the evaporator core; the climate controller cycles or throttles the compressor with it so that the core does not ice up (US6427465B1, US4326386A). Saab's 9-3 uses its own numbers: B0521 02 below 0.2 V and B0522 05 above 4.8 V at the module input, after which the outside temperature serves as a substitute value. HELLA reports that a badly sealed or drifting sensor can freeze the evaporator and choke the airflow. A circuit fault therefore tends to cost cooling comfort rather than leave the car without air.
- What you may notice
- Cooling weak or fluctuating, especially in hot weather
- Airflow drops after a long drive because the evaporator ices up
- Likely causes
- LikelyEvaporator thermistor open, shorted or out of tolerance
- PossibleSensor pushed out of the core or poorly sealed after service
- PossibleConnector at the HVAC housing loose or corroded by condensate
- RareSensor input in the climate control module faulty
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.