What does it mean?
B1226 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Short in the In-car Temperature Sensor Circuit .
Symptoms
- The system behaves as if the cabin were extremely hot and runs full cooling
- The displayed cabin temperature is stuck at one end of the scale
- Blower stays at high speed in AUTO mode
- The AC compressor runs constantly or cycles oddly
- Heating never works properly in cold weather and the fault returns quickly after clearing
Likely causes
- Signal wire chafed against a metal dash brace and shorted to ground
- Internally shorted thermistor reading close to zero ohms
- Water or spilled liquid inside the sensor connector bridging signal and ground
- Harness crushed under a dash bracket or console fastener during previous interior work
- Sensor wire shorted to a nearby 12 V feed, pushing the signal off scale
- Failed input stage in the climate control module
How to fix it
- Read live data and note whether the sensor value sits at the extreme end of its range
- Disconnect the sensor; if the code changes from a short to an open, the sensor itself is at fault
- Measure the thermistor resistance cold, where a near-zero value confirms an internal short
- With the sensor unplugged and the module connector released, test the signal wire for a short to ground and to battery positive
- Inspect the harness route behind the dash for chafe and pinch points, then repair with proper insulation and routing
- Replace the sensor if it is shorted, clear the code, and verify the reading matches actual cabin temperature