What does it mean?
B1213 is a Body (airbags, seat belts, body electronics) fault code. It indicates: An Open in the Rear Evaporator Temperature Sensor Circuit .
Symptoms
- Rear air conditioning blows warm or cools only intermittently
- Rear compressor request cut off as a protection measure against evaporator icing
- Rear temperature display shows dashes or an obviously wrong value
- Rear blower runs normally but no cold air arrives while the front system still works
- Climate fault message with the code stored
Likely causes
- Thermistor inside the rear evaporator temperature sensor open internally
- Sensor probe pulled out of the evaporator core or left unclipped after service
- Connector unplugged, half-latched, or terminals backed out inside the rear HVAC unit
- Wire broken where the harness runs along the floor, sill or headliner to the rear unit
- Corrosion from condensate water sitting in the rear evaporator housing
- Damage during trim, floor covering or rear air conditioning repair work
- Failed input circuit in the rear climate control module
How to fix it
- Read the rear evaporator temperature in live data; an open circuit normally shows an extreme value at one end of the scale
- Unplug the sensor and measure its resistance, comparing it with the temperature/resistance specification
- Fit a known resistance across the connector terminals and see whether the displayed value changes; if it does, the sensor is at fault
- Inspect the connector for corrosion, water and backed-out terminals
- Check continuity of both wires from the sensor connector back to the module
- Repair the harness or replace the sensor, making sure the probe is seated correctly in the evaporator core
- Clear the code, run the rear system and confirm it cools with a plausible temperature reading