What it means
The intake air temperature (IAT) sensor reading does not change plausibly with engine warm-up or after driving begins. Many vehicles share the IAT into the MAF housing; on those, MAF replacement also replaces IAT.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Intake air temperature sensor 1 measures the temperature of incoming air, sometimes from inside the MAF housing. The ECU checks whether its reading changes plausibly with ambient conditions and driving; P0111 sets when the signal is present but does not respond as expected, such as when the sensor drifts or is contaminated.
Common causes
Most likely first.
- Sensor drifting outside specification
- Sensor element coated with oil or dirt
- Sensor element aged beyond calibration window
Symptoms
- Check engine light on
- Hard starting, especially when cold
- Rough idle or hesitation
- Reduced fuel economy
How to diagnose it
- Check freeze-frame data and compare IAT sensor 1's reading with ambient temperature after a cold soak for an initial plausibility check.
- Watch sensor 1's live reading as the engine warms and the vehicle is driven to see whether it responds to changing intake conditions.
- Inspect sensor 1 and its connector for dirt, oil, loose fit, or damaged wiring that could slow or distort the reading.
- If sensor 1 is built into the MAF, compare the MAF data and inspect the shared assembly and connector rather than assuming a separate sensor is fitted.
- Test sensor 1's response and circuit against the manufacturer's specification before replacing the sensor or combined assembly.
Common fixes
- Clean sensor 1 only using a method approved for that sensor.
- Repair a loose connector or damaged wiring at intake air temperature sensor 1.
- Replace a drifting sensor 1 if its response remains outside specification.
- Replace the combined MAF/IAT assembly if testing confirms the integrated sensor has failed.
Can I keep driving?
If the vehicle runs normally, keep driving limited while arranging diagnosis; starting and fuel economy may be affected, especially when cold. Avoid hard acceleration if hesitation develops, since the ECU may be using an inaccurate intake temperature.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.