P0127: Intake Air Temperature Too High
The engine control unit sees an intake air temperature higher than it allows.
Normal risk
Usually drivable, but power may be reduced. Have it checked soon.
Short answer · Can I keep driving with P0127?
Usually yes. The engine may reduce power or ignition advance to prevent knock. Have it checked soon.
What does P0127 mean?
P0127 is often set on turbo engines. The engine control unit measures the air after the intercooler; if it is hotter than expected for the conditions, it stores this code. A blocked or dirty intercooler, a failed intercooler fan or pump on some engines, a boost leak, a faulty air temperature sensor or a wiring fault are typical causes.
What the car does when the code is set
The check engine light comes on and the engine uses a fixed substitute temperature. Most drivers notice no difference. Some cars start less easily in very cold or very hot weather or use slightly more fuel.
How the system works
The intake air temperature sensor is a thermistor whose resistance falls as the air gets warmer. The engine control unit feeds it a reference voltage of about 5 volts and reads how much is left: a high voltage means cold air, a low voltage warm air. The reading is used to correct fuel quantity and ignition timing, because cold air is denser than warm air. If the signal is stuck at either end of its range, the control unit recognises a circuit fault and replaces the reading with a fixed value.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Open circuit or unplugged sensorA broken wire or loose connector makes the reading jump to its coldest value.
- Corroded connectorCorrosion adds resistance to the circuit.
- Faulty sensorThe sensor resistance no longer changes correctly with temperature.
- Wiring damageChafed wires near the intake or engine.
How it is diagnosed
- Compare with outside temperatureWith a cold engine, the intake air temperature should be close to the outside temperature. A reading of about −40 °C usually means an open circuit.
- Check the connectorUnplug the sensor (it is often part of the air-flow sensor) and look for corrosion and bent pins.
- Measure resistance and voltageCompare the sensor resistance at a known temperature and the reference voltage with the service data.
- Repair and clearAfter a repair, clear the code and check that the reading follows the real temperature.
Questions about P0127
Can hot weather set P0127?
Very hot weather and heavy load can push the temperature up, but a healthy cooling system usually stays within limits. If it appears often, check the intercooler and the sensor.
Will this code affect fuel economy?
Slightly. The engine uses a substitute temperature, so the mixture is less precisely matched to the real air density.
Is the sensor part of the air-flow sensor?
On many cars it is, so the whole air-flow sensor is replaced. On others it sits separately in the intake duct or manifold.