What does it mean?
OBD II fault code B1250 is a manufacturer-specific code defined by Ford and many other car makers as Air Temperature Internal Sensor Circuit Failure . This code is set when an issue with a signal from the interior temperature sensor, which is a part of the climate control system, is detected. As the name might suggest, the Air Temperature Internal Sensor measures the temperature inside the car’s cabin.
This is used by the climate control module to adjust the heating or cooling to match the temperature set by the driver. Obviously, only those cars that have an Automatic Climate Control (ACC) will have this sensor, while those where the interior cooling and heating are set manually will not. The working principle behind this sensor – also often called a cabin temperature sensor – is based on electrical resistance.
In essence, the climate control module sends a current through a sensor and monitors the voltage it receives back, which changes depending on the temperature. This is very similar to, for instance, how the intake air temperature sensor works. Be aware other carmakers also may use this code, with different definitions between different makes. This guide applies primarily to Ford vehicles but may also work for some Lincolns and Jaguars, as many of these cars use the same architecture.
Symptoms
- Automatic climate control ignores the set temperature and blows full hot or full cold
- The displayed cabin temperature is missing, frozen, or clearly wrong
- Blower speed does not vary in AUTO mode
- Cabin comfort is unpredictable and needs constant manual correction
- The climate display may show dashes or an error indication
Likely causes
- Open, shorted, or high resistance wiring between the cabin temperature sensor and the climate control module
- Failed thermistor inside the in-car temperature sensor
- Sensor connector unplugged, corroded, or with a spread terminal
- Blocked aspirator tube or a seized aspirator fan, so the sensor never samples representative cabin air
- Harness damage behind the instrument panel after audio, dash, or accessory work
- Faulty sensor input circuit inside the climate control module
How to fix it
- Check the in-car temperature value in live data and compare it with an actual thermometer placed in the cabin
- Locate the sensor behind the dash near its small intake grille and inspect the connector and terminals
- Measure the thermistor resistance at a known temperature and compare with specification
- Check the aspirator tube and fan for dust or debris blockage, since a starved sensor gives false readings
- Test the signal wire for continuity, shorts to ground, and shorts to voltage with both ends disconnected
- Repair the wiring or replace the sensor as indicated, clear the code, and verify the module now tracks cabin temperature