What does it mean?
P1299 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder Head Temperature Sensor High Input .
Symptoms
- MIL (check engine lamp) on, temperature gauge reading low or dropping to cold
- Cooling fans running all the time, or not running when they should
- Rich cold-start behaviour, poor fuel economy and a fuel smell
- Fast idle stays high and the engine never enters closed loop properly
- Overheat protection may fail to engage when it is genuinely needed, which risks engine damage
Likely causes
- Open circuit in the CHT signal wire or a disconnected sensor connector
- Open or high-resistance sensor ground back to the module
- Internally open or failed CHT sensor element
- Corroded or backed-out terminal at the sensor, common in a hot, dirty area
- Signal wire shorted to a voltage source
- On some vehicles the code sets during genuine severe overheating and coolant loss, so real head temperature must be checked before condemning parts
How to fix it
- With the engine cold, compare CHT, coolant temperature and intake air temperature; the values should agree closely
- At the sensor connector, jumper the signal pin to ground: if the reading swings to maximum temperature, the harness and module are good and the sensor is open
- Measure sensor resistance against the manufacturer's temperature and resistance table
- Check the ground circuit resistance from the sensor back to the module
- Inspect the connector for corrosion, heat damage and loss of pin tension
- Confirm the actual head temperature with an infrared thermometer and verify coolant level before replacing anything
- Replace the sensor or repair the open circuit, then verify a normal warm-up curve