What does it mean?
B1225 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Open in the In-car Temperature Sensor Circuit .
Symptoms
- Automatic climate control ignores the set temperature and blows full hot or full cold
- The cabin temperature value on the display is missing, frozen, or clearly wrong
- Blower speed does not modulate in AUTO mode
- Comfort is only achievable by switching to manual settings
- Heating or cooling runs harder than the cabin actually needs
Likely causes
- Broken or cut wire between the cabin temperature sensor and the climate control module
- Sensor connector unplugged, or a terminal backed out of the housing behind the dash
- Internally open thermistor giving an infinite resistance reading
- Corroded pins after moisture reached the connector
- Loss of the shared sensor ground at a splice or module pin
- Open input circuit inside the climate control module
How to fix it
- Check the in-car temperature value in live data; an open circuit normally shows the extreme low end of the scale
- Locate the sensor behind the dash near its small intake grille and confirm the connector is fully seated
- Bridge the two sensor connector pins with a jumper wire; if the reading swings to the hot end, the harness and module are proven good
- Unplug the sensor and measure the thermistor at a known cabin temperature against the resistance table
- Check continuity of the signal and ground wires from the sensor connector to the module connector
- Repair the open wire or reseat the pushed-out terminal, and replace the sensor only if it measures open
- Clear the code and confirm the module displays a plausible cabin temperature