Why does low input mean high temperature?

Because the sensor is a negative temperature coefficient thermistor: its resistance falls as it warms up. It is wired in series with a fixed resistor inside the engine control unit, so a hot sensor with low resistance produces a low signal voltage, and a cold one produces a high voltage. Low input therefore means the control unit is reading an implausibly hot intake, and high input means an implausibly cold one. It catches people out constantly, and it is the same convention on the coolant temperature sensor codes P0117 and P0118.

Can I drive with a P0112 code?

Yes. The control unit falls back on a default intake temperature and the engine runs more or less normally. You may notice slightly awkward cold starting and a little less urgency in cold weather, because the timing is being pulled back to guard against knock the sensor is falsely predicting. It will still fail an MOT on the lamp.

Will P0112 fail an MOT?

Yes, on the lamp rather than the emissions. An illuminated engine malfunction indicator lamp is a major defect under section 8.2.1.2 for petrol cars first used on or after 1 July 2003 and 8.2.2.2 for diesels from 1 July 2008, and 371,859 failures have been recorded against it. The tester has no discretion to weigh up how minor the underlying fault is.

How do I test an intake air temperature sensor?

Leave the car overnight so everything is at ambient temperature, then switch the ignition on and compare the intake air temperature reading with the coolant temperature reading. They should be within a few degrees of each other and of the actual outside temperature. Then unplug the sensor with the ignition still on: the reading should immediately swing to the coldest end of the scale. If it does not move, the signal wire is shorted to earth.

Powertrain code · standard

P0112Intake air temperature sensor reading too hot

Standard definition: Intake Air Temperature Sensor Low Input

Last updated 27 July 2026

Quick answer

The intake air temperature sensor circuit has gone low, which on this type of sensor means the engine control unit is being told the air entering the engine is far hotter than it can be. It is usually a short in the wiring rather than genuinely hot air.

How the car works this out

The intake air temperature sensor is a thermistor whose resistance falls as it gets hotter, wired into a voltage divider in the engine control unit. Cold air gives high resistance and a high signal voltage; hot air gives low resistance and a low voltage. P0112 is the low voltage code, so it means the unit is seeing an implausibly high temperature — often the maximum the scale allows. Since the air going into an engine cannot reach that temperature, the reading is treated as a fault. Most cars set it when the sensor circuit is shorted to earth or the sensor has failed with a collapsed resistance.

What you might notice

Hard starting when the engine is cold
Hesitation or a flat spot in cold weather
Slightly reduced power, as the control unit pulls ignition timing to protect against knock
Marginally worse economy
Often no noticeable symptoms at all beyond the lamp

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1The sensor signal wire shorted to earth, commonly where the loom chafes on a bracket or the intake pipeCommon
How to check: Unplug the sensor with the ignition on. The reading should swing to the coldest end of the scale. If it stays pinned at maximum temperature, the wiring is shorted rather than the sensor being faulty.
2A failed sensor with internally collapsed resistanceCommon
3Water or corrosion bridging the terminals in the connectorPossible
4On engines where the sensor is built into the airflow meter, a fault in the meter itselfPossible
5A previous repair with the wrong sensor, one with a different resistance curveLess common

What to do about it

1Do the unplug test. Disconnecting the sensor with the ignition on should make the reading jump to the cold extreme, and a reading that does not move proves the wiring is at fault.
2Compare the intake air temperature against the coolant temperature after the car has stood overnight. On a properly cold engine the two should read within a few degrees of each other and of the outside air.
3Check whether the sensor is a separate item or part of the airflow meter before ordering anything. On a great many modern engines it is built in, which changes the job entirely.
4Inspect the connector for water and the loom for chafe points against the intake ducting.

Can you keep driving?

Yes

Of all the sensor codes, this is among the least alarming. The control unit substitutes a default air temperature and carries on, and most drivers notice nothing beyond a slightly awkward cold start. The lamp still means an MOT failure, so it needs fixing, but it does not need fixing today.

Will it fail an MOT?

The engine management lamp is the problem here rather than the fault behind it. An illuminated lamp is a major defect for petrol cars first used from 1 July 2003 and diesels from 1 July 2008, with 371,859 recorded failures, and the tester does not weigh up how serious the underlying code is. A false hot-air reading has only a modest effect on the mixture, so the tailpipe figures will usually still pass — but the certificate will say failed regardless.

The light this turns on

Engine management lightThe engine management system has found a fault it cannot correct and has stored a code for it. The car will usually still drive, but an illuminated engine light is an automatic MOT failure on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.

Common questions

Why does low input mean high temperature?: Because the sensor is a negative temperature coefficient thermistor: its resistance falls as it warms up. It is wired in series with a fixed resistor inside the engine control unit, so a hot sensor with low resistance produces a low signal voltage, and a cold one produces a high voltage. Low input therefore means the control unit is reading an implausibly hot intake, and high input means an implausibly cold one. It catches people out constantly, and it is the same convention on the coolant temperature sensor codes P0117 and P0118.
Can I drive with a P0112 code?: Yes. The control unit falls back on a default intake temperature and the engine runs more or less normally. You may notice slightly awkward cold starting and a little less urgency in cold weather, because the timing is being pulled back to guard against knock the sensor is falsely predicting. It will still fail an MOT on the lamp.
Will P0112 fail an MOT?: Yes, on the lamp rather than the emissions. An illuminated engine malfunction indicator lamp is a major defect under section 8.2.1.2 for petrol cars first used on or after 1 July 2003 and 8.2.2.2 for diesels from 1 July 2008, and 371,859 failures have been recorded against it. The tester has no discretion to weigh up how minor the underlying fault is.
How do I test an intake air temperature sensor?: Leave the car overnight so everything is at ambient temperature, then switch the ignition on and compare the intake air temperature reading with the coolant temperature reading. They should be within a few degrees of each other and of the actual outside temperature. Then unplug the sensor with the ignition still on: the reading should immediately swing to the coldest end of the scale. If it does not move, the signal wire is shorted to earth.

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