B0255HVAC Air Temperature External Sensor Circuit
- Generic OBD-II code · Body
- How the car detects it
- B0255 shows up in no publicly available J2012 source. Saab's 9-3 uses it for a door motor: B0255 06 reports the right vent door motor circuit open or grounded, B0256 01 the B+ short on that motor. By its title, though, the code means the outside air sensor; that component also has the codes B0158 and B0159. HELLA's ambient sensor is an NTC resistor read through a voltage divider, rated −40 to +65 °C with a time constant under 35 s, and the module turns its resistance into a temperature using the sensor curve. Mounted behind the grille or under a mirror, it suffers from stone chips, salt and pinched wiring. Climate control uses the value to choose mode and fan speed, so a fault means poor regulation and a blank or wrong outside temperature.
- What you may notice
- Outside temperature display shows dashes or an implausible value
- Automatic climate control regulates poorly, especially in cold or hot weather
- Likely causes
- LikelyOutside sensor broken by stone impact or corroded by road salt
- PossibleSensor wiring behind the bumper pinched or torn, often after front-end repairs
- RareMoisture in the sensor plug changing the measured resistance
- Repair
- Easy · Often possible to do yourself.Typical cost: €25 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.