What does it mean?
B1251 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Compartment Temperature Sensor Circuit Open .
Symptoms
- The set temperature has no effect and the system blows at one extreme
- The cabin temperature reading is absent or pinned at the coldest value
- The blower does not modulate in automatic mode
- Heating or air conditioning runs harder than needed, increasing fuel consumption
- Acceptable comfort can only be reached using manual settings
Likely causes
- Broken or cut wire in the cabin temperature sensor circuit
- Connector disconnected or a terminal pushed out of its housing behind the dash
- Internally open thermistor giving an infinite resistance reading
- Corroded pins after moisture entered the connector
- Loss of the sensor ground where it joins a shared splice
- Open input circuit inside the climate control module
How to fix it
- Confirm the fault in live data; an open cabin sensor normally shows the extreme low end of the scale
- Jumper the two sensor connector pins, and if the reading swings to the hot end the harness and module are proven good
- Measure the sensor thermistor resistance and compare it with the temperature table
- Check continuity of the signal and ground wires from the sensor connector to the module connector
- Repair the open wire or reseat the terminal that has backed out of the connector
- Replace the cabin temperature sensor only if it measures open, then clear the code and verify the reading