B0255 code meaning
HVAC Air Temperature External Sensor Circuit
What B0255 means
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.
B0255 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0255
- Outside temperature display shows dashes or an implausible value
- Automatic climate control regulates poorly, especially in cold or hot weather
Common causes of B0255
- Most likelyOutside sensor broken by stone impact or corroded by road salt
- PossibleSensor wiring behind the bumper pinched or torn, often after front-end repairs
- Less likelyMoisture in the sensor plug changing the measured resistance
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ambient temperature sensorHvac control module
What each part of B0255 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 55 | The exact fault in that area. |
What to do next
- Note B0255 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0255
What does B0255 mean?
B0255 means "HVAC Air Temperature External Sensor Circuit". B0255 shows up in no publicly available J2012 source. It is a generic code, so it means the same on every make.
Is it safe to drive with B0255?
B0255 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0255 fail an emissions test?
B0255 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0255 to fix?
Difficulty: easy. A typical repair takes 0.2 to 1 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will B0255 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.