What does it mean?
B1253 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Compartment Temperature Sensor Circuit Short (Body Ground) .
Symptoms
- The climate system behaves as if the cabin were extremely hot and runs full cooling
- The cabin temperature reading is stuck at the high end of the scale
- Blower stays at high speed in AUTO mode
- Heating never works properly in cold weather
- The fault returns quickly after being cleared
Likely causes
- Signal wire chafed against a metal dash brace and shorted to body ground
- Internally shorted thermistor inside the cabin temperature sensor
- Water or spilled liquid inside the sensor connector bridging signal and ground
- Harness crushed under a dash bracket, seat rail, or console fastener
- Aftermarket accessory wiring tapped into or pinching the climate harness
- Failed input circuit inside the climate control module pulling the signal down
How to fix it
- Look at the cabin temperature in live data; a short to ground normally shows the hottest value
- Unplug the sensor, and if the reading swings to the opposite extreme the sensor is internally shorted
- Measure the thermistor resistance cold, where near zero ohms confirms an internal short
- With both ends disconnected, check the signal wire for continuity to body ground
- Inspect the harness route behind the dash for chafe points and repair with insulation and correct routing
- Replace the sensor if it is shorted, clear the code, and confirm the reading matches actual cabin temperature