P0112 Code: Intake Air Temperature Sensor 1 Circuit Low
The IAT signal is near zero volts, so the PCM believes the intake air is scorching hot, usually a short.
At a glance
Severity: Low
- Meaning
- Intake Air Temperature Sensor 1 Circuit Low
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$450
- DIY difficulty
- Easy
The IAT sensor's resistance, and with it the voltage the PCM reads, falls as the air gets warmer. A voltage close to zero would mean air far hotter than any intake ever sees, so P0112 sets when the signal stays below the lower limit, usually a few tenths of a volt, and live data shows a maxed-out temperature, often somewhere around 250 to 300°F depending on the vehicle. Unlike the open circuit behind P0113, this fault needs a path to ground: the signal wire rubbed through against the engine or body, a thermistor that has shorted internally, or moisture and corrosion bridging the pins inside the connector. Believing the air is extremely hot, the PCM may retard spark and trim boost to protect against knock until it substitutes a default value.
Can I keep driving? Safe to drive at normal loads. Expect the engine to feel a bit sluggish, and cold starts may be harder, because the PCM enriches less when it thinks the incoming air is hot.
How to read P0112
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 12 Specific fault
Symptoms
- Check engine light on
- Live data shows a maxed-out IAT, such as 250°F or more, even on a cold engine
- Hard or rough cold starts, most noticeable in winter
- Sluggish acceleration from retarded spark timing
- Reduced boost on turbocharged engines
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- IAT thermistor shorted internally
- Signal wire chafed through and touching engine, bracket or body ground
- Water, oil or corrosion bridging terminals inside the connector
- Harness pinched during air box, intake or MAF replacement
- Replacement sensor with the wrong resistance curve
- PCM input shorted internally
Diagnosis step by step
Confirm the reading on a cold engine
After an overnight cool-down, an IAT of 250°F or more while coolant temperature matches the weather confirms a circuit problem, not real heat. Don't confuse it with normal heat soak: right after a hot shutdown, a manifold-mounted sensor can honestly read 140 to 160°F.
Tools: OBD-II scanner
Unplug the sensor and watch live data
Key on, disconnect the IAT, or the MAF or combined MAP sensor it lives in. The reading should swing to the coldest value, about -40°F. If it does, the short is inside the sensor; if it stays pinned at the maximum, the signal wire is grounded somewhere in the harness.
Tools: OBD-II scanner
Measure the sensor's resistance
A good sensor reads thousands of ohms at room temperature. A shorted one reads close to zero, or far lower than it should for the temperature it's sitting at. On a MAF with integrated IAT, measure across the two temperature pins shown in the wiring diagram.
Tools: Multimeter
Check the signal wire for a short to ground
With the battery, sensor and PCM disconnected, measure from the signal wire to engine ground: it should read open. Any continuity means damaged insulation, so inspect the harness where it's clipped to the air box, runs past the throttle body or rests on metal brackets.
Tools: Multimeter
Inspect the connector for contamination
Look for water, engine oil from a leaking valve cover or PCV hose, and white or green corrosion between the pins. A contaminated connector can create a leakage path that pulls the signal down even though sensor and wiring test fine when dry.
Tools: Flashlight
Where the parts are
- 1MAF sensor
- 2Turbocharger
- 3Throttle body
- 4Intake manifold
- 5Fuel injector
- 6EGR valve
- 7Fuel pump
- 8Thermostat
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Dry and clean the connector | Yes | $0–$40 |
| Replace standalone IAT sensor | Yes | $25–$120 |
| Replace MAF sensor with integrated IAT | Yes | $150–$450 |
| Repair grounded signal wire | No | $100–$300 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
The car fails the OBD-II check in state emissions programs while the check engine light is on. Once the short is repaired and the code cleared, drive normally for a few days so the readiness monitors can finish.
Frequently asked questions
My IAT reads 150°F after sitting in traffic. Is that P0112?
No, that's normal heat soak, especially on sensors mounted in the intake manifold. P0112 needs a reading beyond any real intake temperature, typically near the scanner's maximum, and on a cold engine it shows that same extreme value.
Why is my car harder to start in winter with P0112?
The PCM uses air temperature to decide how much extra fuel a cold start needs. If it believes the air is very hot, it adds less fuel than a freezing morning demands, so the engine cranks longer or stumbles until it warms up.
Can I unplug the IAT sensor to get rid of the hot reading?
Unplugging simply trades P0112 for P0113, and the PCM then runs on a default temperature. It can confirm whether the sensor or the wiring is shorted, but it isn't a repair.
Is P0112 always a bad sensor?
Most often, but not always. A signal wire rubbed through to ground or a connector full of water gives exactly the same reading. The unplug test tells you which one you're dealing with before you buy parts.