P0110
PowertrainIntake Air Temperature Sensor 1 Circuit Malfunction
The intake air temperature sensor circuit is sending the ECU a signal that's either missing or doesn't make sense. The IAT sensor tells the engine how hot the incoming air is, which feeds into the fuelling calculation, so when that reading goes haywire the engine ends up guessing at the mixture. On most cars the symptoms are mild, often just a light on the dash and a small dip in economy, but it's usually a cheap fix once you've found whether it's the sensor or the wiring.
ⓘ Information only. This page provides general educational information about fault code P0110. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0110 mean?
P0110 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Intake Air Temperature Sensor 1 Circuit Malfunction.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, frequently the only thing you'll actually notice
- • Fuel economy down a little, often around 5-10%, most obvious on a regular commute
- • Lumpy idle just after a cold start while the engine sorts its fuelling out
- • A bit of hesitation or flat spot when you put your foot down
- • Engine running slightly rich or lean, enough to feel off but not dramatic
- • Quite often no driveability problem at all beyond the dash light
Possible causes
Causes commonly associated with P0110, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Faulty IAT sensor, the thermistor inside drifts or fails with age and heat cycling. This is the usual culprit
- 2. Corroded, loose, or water-damaged connector at the sensor, very common where the plug sits in the engine bay
- 3. Chafed or broken signal wire, often rubbed through by vibration or heat near the intake pipework
- 4. Sensor element coated in oil or dirt, usually traced back to a neglected air filter or an oily breather
- 5. Open or short in the harness between the sensor and the ECU
- 6. Poor earth or a low 5V reference feed to the sensor
- 7. Rarely, an internal ECM/PCM fault, only worth considering once everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the freeze frame data with a scanner and note what the IAT was reporting when the code set. A reading stuck at a daft value like -40C or 140C points straight at an open or shorted circuit
- 2. Get your hands on the connector and sensor. Look for green corrosion, pushed-back pins, melted plastic, or an oily film on the sensor tip. Plenty of P0110s are a dirty plug and nothing more
- 3. With the key on, back-probe the connector and check you've got the 5V reference and a clean earth. No reference voltage and you're chasing a wiring or ECM fault, not the sensor
- 4. Measure the sensor's resistance cold and compare to spec, roughly 2-3 kOhm at around 20C. Way out, or open circuit, means the sensor is done
- 5. If the sensor reads correctly on the bench but you still have the code, do continuity and resistance checks on the wiring back toward the ECU. Wiring resistance wants to be at or near zero, certainly under 1 kOhm
- 6. Wiggle-test the harness with live data running. An IAT reading that jumps about when you flex the loom tells you exactly where the break is
Common questions about P0110
Will this stop my car passing its MOT? +
The code on its own isn't a fail, but if the engine warning light is on when the tester plugs in or eyeballs the dash, that's a fail on the spot under the current rules. Sort the actual fault, then clear the light and drive a few warm-up and cooldown cycles so it doesn't come straight back during the test. If the mixture has drifted badly enough to push your emissions up at the tailpipe, that side of the test can fail too, though that's less common with this code.
What's it likely to cost me? +
This is usually one of the cheaper codes to put right. A standalone IAT sensor is often £15-£40 for the part, and on many cars it's a five-minute swap. The catch is that on a lot of modern engines the IAT is built into the MAF sensor, and a combined MAF/IAT unit runs £80-£200 or more. An independent garage will typically charge half an hour to an hour of labour to diagnose and fit; a main dealer will want more and may push a genuine part. Wiring repairs depend entirely on how much loom needs sorting, anywhere from £40 to a few hundred.
How do I work out whether it's the sensor or the wiring on mine? +
Start at the connector. Clean any corrosion off, refit it, and see if the code clears, because a dodgy plug is the most common cheap cause. If it comes back, measure the sensor's resistance cold against spec. A sensor that's open circuit or wildly out of range is your answer. If the sensor checks out fine but the ECU still isn't seeing it, you've got a wiring or reference voltage problem, and a wiggle-test of the loom while watching live data will usually show you where.
Can I clean or replace the sensor myself? +
Often yes. If it's a standalone IAT in the intake pipe, unplug it, undo the clip or bolt, and swap it. Cleaning is worth a try first if the tip looks oily or dusty, use proper MAF/sensor cleaner spray and let it dry fully before refitting, never wipe the element with a rag. Where the IAT is part of the MAF assembly the job is just as simple physically, but the part costs a lot more, so it's worth confirming with a multimeter that the sensor really is the problem before buying one.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →