P0112
PowertrainIntake Air Temperature Sensor 1 Circuit Low Input
Most of the time this comes down to a dodgy connector or chafed wiring at the intake air temperature sensor, with the actual sensor failing internally a close second. The IAT sensor is just a thermistor that changes resistance with air temperature, and the ECU reads that as a voltage. When the voltage drops lower than the ECU expects, it reads it as impossibly hot intake air and logs P0112. That low reading usually means the signal wire has shorted to earth or the sensor's gone open the wrong way.
ⓘ Information only. This page provides general educational information about fault code P0112. 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 P0112 mean?
P0112 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Intake Air Temperature Sensor 1 Circuit Low Input.
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, sometimes with no obvious change in how the car drives
- • Slightly worse fuel economy because the ECU thinks the air is hotter than it is and trims the mixture
- • Rough or lumpy idle, more noticeable once the engine has warmed up
- • Hesitation or a flat spot when you put your foot down
- • A few cars stumble or stall at low revs, particularly pulling away from junctions
- • Faint petrol smell from the exhaust if it's running rich
Possible causes
Causes commonly associated with P0112, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded or loose connector at the sensor, the single most common reason for a low signal. Water and road muck get into the plug and bridge the pins
- 2. Signal wire chafed through and shorting to earth somewhere along the harness, which pulls the voltage straight down
- 3. The IAT sensor itself failed internally. The thermistor degrades and the resistance collapses
- 4. On many cars the IAT is built into the MAF sensor, so a failed MAF can throw this code too
- 5. Bent or pushed-back pin in the connector giving a poor or intermittent contact
- 6. ECU reference voltage or signal processing fault, rare, only suspect this 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 live data and look at the IAT reading with the engine stone cold. If it's showing something daft like 140°C on a frosty morning, the circuit is the problem, not the actual temperature
- 2. Unplug the sensor and inspect both halves of the connector for green corrosion, water, or pins that have been pushed back. This catches a good share of these
- 3. With the ignition on, back-probe the connector and check for roughly 5 volts on the reference wire and a clean earth. No reference voltage points at the wiring or ECU
- 4. Measure the sensor resistance across its two pins. Around 2,000 to 3,000 ohms at 20°C is typical, though it varies by make. A near-zero or stuck reading means the sensor's done
- 5. Do a wiggle test on the harness near the sensor while watching live data, looking for the value jumping around, which gives away a chafed wire or intermittent short to earth
Common questions about P0112
How do I know if it's the sensor or just the wiring and plug? +
Check the connector first, because corroded or wet plugs cause a big chunk of P0112s and cost nothing to sort. Unplug it and measure the sensor's resistance with a multimeter. If the resistance is sensible for the temperature, around 2,000 to 3,000 ohms at 20°C, the sensor is fine and your fault is in the wiring or connector. If it reads near zero or doesn't change as the sensor warms, replace the sensor. On cars where the IAT is part of the MAF, you may end up replacing the whole MAF unit.
How long does this job actually take? +
A standalone IAT sensor that you can get a hand to is a ten to fifteen minute swap, often a single plug and one screw. Cleaning or repairing a corroded connector is a similar quick job once you've found it. If the fault is a short to earth buried in the loom, expect a garage to spend an hour or more tracing it, and that's where the bill climbs. A combined MAF and IAT replacement is usually under half an hour.
Is a cheap aftermarket sensor worth fitting or should I stick with OEM? +
For a plain IAT thermistor, a decent quality aftermarket part from a known brand is fine and saves you a fair bit over main dealer prices. Skip the bargain-basement no-name ones, they often read slightly off and you can find yourself chasing fuelling niggles afterwards. Where the IAT is integrated into the MAF, I'd lean towards OEM or a reputable brand like Bosch, because a poor MAF causes far more grief than a cheap standalone temp sensor ever would.
Is it safe to carry on driving with this showing? +
You can drive it short term and most cars won't leave you stranded, but the ECU is fuelling off a wrong air temperature reading so it'll run richer or leaner than it should. That means worse economy and, over time, more soot and wear. If it's idling rough or stalling, get it looked at sooner rather than later. And a warning light that's on at MOT time can affect your result, so don't let it sit indefinitely.
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 →