Code guide
P0113 — intake air temperature circuit high
The intake air temperature sensor is a thermistor, and its failure math is elegant: a broken circuit reads as the coldest value possible. Which is why a live reading of -40° isn't a weather report — it's the diagnosis.
IAT circuit · Air metering · Often paired with P0102
The short version
P0113 means the intake air temperature signal sat at the high-voltage end of its range — which, for this sensor's electronics, is the reading it produces when the circuit is broken. An unplugged connector, a snapped wire, a corroded pin, or a failed sensor element all look identical to the computer: infinitely cold air.
The suspects, in order:
- The connector — especially if air-filter, intake, or MAF work happened recently.
- The wiring to it — chafe and breaks where the harness flexes.
- The sensor element itself, failed open.
This is one of the cheapest code families on the car to put right — and one glance at live data usually confirms it.
Reading codes and live temperature data are free in Fixiom — always, no credits and no subscription.
Why -40° means open circuit
The sensor is a thermistor — a resistor whose resistance falls as it warms. The computer feeds the circuit a reference voltage and reads temperature from how much comes back. Cold air = high resistance = high voltage; hot air = low resistance = low voltage.
Break the circuit entirely and the computer sees the reference voltage undisturbed — the highest reading possible, which its table translates as the coldest temperature it knows: -40° (the one temperature that's the same number in Fahrenheit and Celsius, which is why that specific value shows up on scan tools everywhere).
So a pinned -40° isn't a strange sensor reading. It's the electrical signature of an open circuit, drawn in temperature units. (The mirror-image code, P0112, is the circuit shorted — pinned impossibly hot.)
The one-glance test
- Put intake air temperature on screen. Reading -40° (or something equally absurd like 300°) with the engine running: circuit fault confirmed, exactly as the code claims. Move to the connector.
- The cold-soak sanity check, for subtler cases: after the vehicle sits overnight, intake air temperature, coolant temperature, and the actual weather should all agree within a few degrees before startup. A sensor that disagrees wildly with its neighbours is lying.
- The warm-idle drift check: parked and idling, the intake picks up engine-bay heat, so a healthy IAT slowly climbs above ambient. A reading that never moves at all, ever, is suspicious even when it's plausible.
- Then the connector, engine off and cool: unlatch, inspect both halves for bent or corroded pins and oil intrusion, check the harness where it flexes, reseat to the click. If the live reading snaps from -40° to a believable number, you just watched the fault get fixed.
Where the sensor actually is
On most modern engines the IAT sensor is built into the mass air flow sensor assembly and shares its connector — a standalone IAT screwed into the intake tract is the older arrangement, though plenty of vehicles still have one (and some turbocharged engines have two).
The integration has a diagnostic consequence worth knowing: P0113 arriving together with P0102 — MAF signal low — almost always means the shared connector or harness took both signals out at once. One plug, one fault, two codes. It also explains a classic head-scratcher: "my IAT code started after I cleaned the MAF" usually means the shared connector didn't go back on quite right.
What it does to the engine
Air density depends on temperature, so the computer uses this reading to fine-tune fuelling and spark. Told the air is -40° — far denser than reality — it errs rich and conservative. In practice, with the fault present you may notice:
- Slightly rough or rich running, occasionally a fuel smell, and worse economy.
- Harder starts, particularly in genuinely cold weather where correct temperature compensation matters most.
- Often, honestly, very little — many computers substitute a modelled default once the code sets, and the car masks the fault well. The emissions inspection won't be fooled, though: a stored code with the light on is still a fail.
It's drivable. It's also usually a connector reseat or an inexpensive sensor — the ratio of fix-cost to nuisance is about as good as OBD2 gets.
What a phone adapter can't see
What it genuinely gives you: the live reading whose -40° pin is the diagnosis, the cold-soak comparison against coolant temperature and the weather, the freeze frame, and any paired codes that move the suspicion onto a shared connector.
What it cannot do:
- Measure the sensor's resistance to confirm the element itself — that's a meter across its pins against a temperature spec.
- Find the break in a harness — eyes, fingers, and sometimes a wiring diagram.
- Distinguish sensor from wiring definitively. The data proves the circuit is open; which piece of the circuit takes the meter.
Common questions
What does P0113 mean?+
The intake air temperature circuit read at the high-voltage end of its range, which is what an open circuit looks like — an unplugged connector, broken wire, corroded pin, or failed sensor element. The computer translates that as impossibly cold air, typically displaying -40°.
Why does my intake temperature read -40 degrees?+
Because the circuit is open. The sensor is a thermistor: colder air means higher voltage back to the computer, and a broken circuit returns the full reference voltage — the coldest reading on the table. -40° is the electrical signature of a break, not a temperature.
Can I drive with P0113?+
Yes — the computer substitutes a default and errs rich, so you may notice slightly rough running, harder cold starts, and worse economy, or often very little at all. It still fails an OBD2 emissions inspection, and the fix is usually cheap, so there's little reason to live with it.
Why do I have P0113 and P0102 at the same time?+
On most modern engines the IAT sensor lives inside the MAF assembly and shares its connector — so one connector or harness fault silences both signals at once. Two codes, one plug. Check that connector before suspecting either sensor.
Where is the intake air temperature sensor?+
Most commonly built into the mass air flow sensor in the intake tube; on other vehicles it's a small standalone sensor in the intake tract, and some turbocharged engines carry two. If it's the integrated kind, its problems and the MAF's arrive through the same connector.
How do I know if it's the sensor or the wiring?+
Live data proves the circuit is open; splitting sensor from wiring takes a meter. A quick practical filter first: inspect and reseat the connector with the engine off — if the reading snaps from -40° to something believable, it was the connection all along.
Related guides
- P0102 — MAF signal low — a circuit code, not a cleaning code. Start at the connector.
- Cleaning a MAF sensor — How to clean it properly — and how to tell first whether it's actually the problem.
- P0171 — System too lean — where fuel trims tell you the answer in about two minutes.
-40° isn't a temperature. It's a broken wire, in disguise.
Live temperature data, codes, and freeze frames are free in Fixiom — always. Some diagnoses really are one glance long.