Faulty intake air temperature sensor reading falsely high; Damaged, corroded or loose connector at the IAT sensor; Wiring fault such as a short to ground or chafed, shorted or open signal wire; Genuine excessive intake heat from a missing or damaged air intake duct, heat shield or cold-air feed; Heat soak from a recent hot shutdown or very high underbonnet temperatures, affecting sensor readings; Fault in the engine control unit's sensor input or reference voltage supply; Sensor integrated in the mass airflow sensor failing (depends on model and engine).

P0127

Intake Air Temperature Too High.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
27: FaultThe specific fault in that area

What it means

P0127 means the engine control unit has seen an intake air temperature that is higher than expected for the operating conditions. The IAT sensor signal has either gone beyond a plausible limit or stayed far hotter than ambient and coolant temperature suggest, typically after a cold start or once the engine has had time to settle. The cause may be genuine heat in the intake or a fault in the sensor or its circuit.

Symptoms

Engine warning light on
Rough or unsteady idle
Hesitation or reduced power
Poor fuel economy
Hard starting or extended cranking when cold
Black smoke or a rich-running smell in some cases

Possible causes

Faulty intake air temperature sensor reading falsely highlikely
Damaged, corroded or loose connector at the IAT sensorlikely
Wiring fault such as a short to ground or chafed, shorted or open signal wirepossible
Genuine excessive intake heat from a missing or damaged air intake duct, heat shield or cold-air feedpossible
Heat soak from a recent hot shutdown or very high underbonnet temperatures, affecting sensor readingspossible
Fault in the engine control unit's sensor input or reference voltage supplyrare
Sensor integrated in the mass airflow sensor failing (depends on model and engine)possible

How to diagnose

Read the stored and pending codes and note the freeze frame data, including IAT, coolant temperature, engine speed and load when the fault set.
Check live data with the engine cold: IAT should be close to coolant temperature and ambient temperature. A reading far above these points to a sensor or circuit fault.
Look over the air intake path for missing, split or disconnected ducting, displaced heat shields and anything blocking the cold-air feed.
Inspect the IAT sensor connector and wiring for corrosion, bent pins, loose fit, chafing or heat damage.
Unplug the sensor and watch the live reading; it should move to the extreme cold or default value. If it does not, suspect a wiring or control unit fault.
Measure the sensor resistance and compare it with the manufacturer's temperature table; test the signal and reference supply and the ground wiring for continuity and shorts.
Check whether the sensor is separate or built into the mass airflow sensor on this model, as this changes what needs replacing.
Clear the code and road test, watching IAT readings as the engine warms up to confirm they stay plausible.

How to fix

Replace the IAT sensor, or the combined airflow sensor assembly where the sensor is not available separately.
Repair or replace the damaged connector terminals, and clean any corrosion.
Repair the wiring fault, including any shorted, chafed or open circuits, to manufacturer specification.
Refit or replace missing or damaged intake ducting, heat shields and cold-air feed components.
Repair the control unit input or power supply fault only after the sensor, wiring and supply have been proven good.

Can I keep driving?

Low severity

The car can usually be driven short term, but fuel economy and driveability may suffer because the control unit may be using an incorrect air temperature. Book it in soon to prevent poor running and further faults.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.