What does it mean?
B1229 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Open in the Sunlight Sensor Circuit .
Symptoms
- The cabin gets noticeably hotter than the set temperature on sunny days because the system does not compensate for sunload
- Blower speed and vent temperature do not increase when the sun is strong
- AUTO mode feels underpowered in bright weather but normal at night or in the shade
- On dual zone systems the left and right temperature balance no longer shifts with sun position
- No other climate function is affected
Likely causes
- Broken or disconnected wire between the sunload sensor and the climate control module
- Sensor connector unplugged or a terminal pushed back after dash trim removal
- Internally failed photodiode inside the sunload sensor
- Harness damage where the wiring runs under the dash pad
- Corroded connector after a windshield leak or heavy condensation
- Faulty sunload input circuit inside the climate control module
How to fix it
- Check the sunload value in live data, comparing a shaded reading with one in direct sunlight
- Pry the sensor out of the dash top and inspect its connector and pins for damage or corrosion
- Verify the reference voltage at the connector with the ignition on
- Check continuity of the signal and ground wires back to the climate control module
- Repair the broken wire or reseat the terminal, then retest the live value under strong light
- Replace the sunload sensor if the circuit is proven good but the value never changes