P0113 Code: Intake Air Temperature Sensor 1 Circuit High

What the P0113 code means

The IAT sensor is a negative temperature coefficient thermistor: its resistance drops as the air heats up. The computer applies a five volt reference through an internal resistor and measures how much voltage is left in the circuit. Cold air means high resistance and high voltage. Hot air means low resistance and low voltage.

When that voltage rises above the programmed upper limit, around 4.6 volts sustained, the computer decides the circuit is open and stores the P0113 code. In other words, the sensor is telling it the intake air is at impossible temperatures, far below any real condition.

This data is used to correct for air density and to adjust the mixture and the ignition timing, so a wrong value makes cold starts and fuel economy worse, although it does not stop you from driving.

It is worth knowing the real effect of this sensor on how the engine runs, because it is usually underestimated. The computer uses the air temperature to work out the air density: cold air is denser and holds more oxygen per liter than hot air. With that figure it corrects the amount of fuel and, on many engines, the ignition timing as well.

When the sensor reports an absurdly low temperature, the computer assumes very dense air and enriches the mixture permanently. That is where the higher fuel use and the hard starting come from, even if the engine seems to run normally.

P0113 code symptoms

• Check engine light on.
• Hard starting when cold, or a mixture that is too rich.
• Slightly higher fuel use.
• On some vehicles, cooling fans running all the time.
• An absurd intake temperature reading on the scan tool, such as minus 40 degrees with the engine hot.
• A permanently enriched mixture, with constantly higher fuel use.
• More conservative ignition timing, with a slight loss of response.

Likely causes of the P0113 code

1. Connector unplugged or not fully seated, very common after earlier work on the intake.
2. Broken wire or intermittent contact in the signal or ground circuit.
3. Connector pins that are corroded, open or pushed back.
4. IAT sensor failed internally with an open circuit.
5. Faulty sensor built into the MAF, on vehicles where both share one body.
6. Failure of the ground circuit shared by several sensors, which then usually sets other codes at the same time.
7. Water in the connector after an engine wash, which corrodes the pins and opens the circuit.
8. Sensor broken during installation, from forcing it into a plastic housing.
9. Wire broken inside the insulation in the stretch that runs along the intake boot, subject to vibration.

How to diagnose the P0113 code step by step

1. Read the intake temperature in live data with the engine cold. It should be close to the ambient temperature. A value of minus 40 degrees (minus 40 F as well) confirms the open circuit.
2. Inspect the connector. Unplug it, check that the pins are not green or pushed back, and plug it back in firmly.
3. Jumper the two pins of the connector with the key on and watch the scan tool reading. If it jumps to a very high temperature, the wiring is good and the sensor is the failed part.
4. Measure the sensor resistance with a multimeter and compare it with the reference table.
5. Check the 5 volt reference on the signal pin and the continuity of the ground to the computer.
6. Wiggle the harness with the engine running while watching the reading. A momentary jump gives away a wire broken inside its insulation.
7. Compare the reading with the engine fully cold. It should match the ambient temperature within a few degrees.
8. Flex the stretch of wire that runs along the intake boot while watching the reading, to find internal breaks.
9. Find out whether the engine was washed recently. It is a common cause of corrosion in this connector.

How to fix the P0113 code

• Plug the sensor back in if it was loose and clean the pins with electrical contact cleaner.
• Repair or replace the damaged stretch of wire, splicing with solder and heat shrink tubing instead of quick connectors.
• Replace the IAT sensor if the jumper test confirms the wiring is good.
• Replace the MAF assembly with the built-in IAT when the sensor is not sold separately.
• Clean and tighten the shared ground point if several sensors are affected.
• Dry and clean the connector if water got in, and protect it with dielectric grease.
• Replace the stretch of wire if flexing it reproduces the fault, instead of splicing it.
• Tighten the sensor gently in plastic housings so you do not crack it during installation.

After the repair, clear the P0113 code and check that the temperature shown with the engine cold matches the ambient temperature.

Technical reference data

Approximate resistance values for a typical IAT sensor:

• Voltage that sets the code: above 4.6 V sustained. The circuit works on a 5 V reference.
• With the engine cold, the reading should match the ambient temperature within about 5 degrees C (9 degrees F).
• Cold air is denser: a falsely low reading enriches the mixture permanently.

Brand-specific notes

On many modern vehicles the IAT sensor is not a separate part. It comes built into the MAF sensor or into the manifold pressure sensor. Check how your engine is set up before you order the replacement.

This is one of the cheapest codes to fix in the whole OBD2 system. Before you order anything, unplug the sensor and plug it back in firmly: a poorly seated connector explains a good share of the cases.

Frequently asked questions about P0113