P0110 & P0113: Intake Air Temperature Sensor Circuit — Diagnosis & Fix

How the IAT Sensor Works

The IAT sensor is a thermistor — a resistor that changes its resistance based on temperature. Nearly all automotive IAT sensors are negative temperature coefficient (NTC), meaning resistance decreases as temperature increases.

• At -40°F (-40°C): ~100,000 ohms — very high resistance, very low current flow, very high voltage signal
• At 68°F (20°C): ~2,500-3,000 ohms
• At 212°F (100°C): ~180-200 ohms — low resistance, high current flow, low voltage signal

The PCM sends a 5V reference through a pull-up resistor inside the PCM, and the IAT sensor pulls that voltage down based on its resistance. The resulting voltage tells the PCM the intake air temperature, which it uses to fine-tune fuel delivery and spark timing. Cold air is denser, so the engine needs more fuel. Hot air is thinner, so it needs less.

The Unplug Test

This is the most powerful move for any temperature sensor code. Here is the logic:

If you have P0113 (high voltage / cold reading): The sensor circuit is reading as if it is open (infinite resistance = cold). Unplugging the sensor should not change anything — it is already acting like an open circuit. If the reading does NOT change when you unplug it, the sensor wire is already open somewhere or the connector is not making contact. Probe the connector pins for corrosion, spread pins, or a backed-out terminal.

The real test: With the IAT unplugged, take a short jumper wire and connect the signal pin to the ground pin at the harness connector. This puts zero resistance across the circuit — the PCM should now see maximum temperature (very low voltage, near 0V). If it does, you just proved the wiring and the PCM are both good. The sensor is open internally.

If you jumper the pins and the voltage does NOT drop — you have a wiring issue. The signal wire or ground wire is broken between the connector and the PCM. Trace the wiring.

Resistance vs Temperature Check

Remove the IAT sensor and measure its resistance with an ohmmeter. Compare to the temperature:

If the resistance is OL (open line) at room temperature, the sensor is bad. If the resistance matches the chart but the PCM still shows a wrong temperature, the wiring between the sensor and PCM has a problem.

The Cold Soak Comparison Trick

This is one of the best diagnostic techniques most techs never use. After the vehicle sits overnight (cold soak), all temperature sensors should read within a few degrees of ambient air temperature. Before you start the engine:

1. Connect your scan tool and read IAT, ECT (engine coolant temperature), and ambient air temp if available
2. All three should be within 5-10°F of each other — they are all sitting at the same temperature
3. If IAT reads 150°F and ECT reads 72°F on a cold morning, the IAT sensor is lying — it has shifted out of calibration or has an intermittent short
4. If IAT reads -40°F and ECT reads 72°F, the IAT circuit is open (P0113 territory)

This technique catches sensors that are reading within the "plausible" range (so they do not set a code) but are still inaccurate enough to cause driveability problems. A sensor that reads 30°F high at cold soak will be 30°F high at operating temperature too.

Step-by-Step Diagnosis

Step 1: Check Live Data at Cold Soak

Compare IAT to ECT and ambient. They should match within 5-10°F. If the IAT reads -40°F, you have an open circuit.

Step 2: Inspect the Connector

Corrosion, water, spread pins, and backed-out terminals are the most common connector failures. On vehicles where the IAT is in the intake duct (not the manifold), moisture from condensation is a frequent issue.

Step 3: Unplug and Jumper Test

Unplug the sensor. Jumper signal to ground at the harness connector. If the scan tool now reads maximum temperature (low voltage), wiring and PCM are good — replace the sensor. If voltage does not change, trace wiring.

Step 4: Check if IAT is Integrated with MAF

On many 2005+ vehicles, the IAT is built into the MAF housing. This means an IAT failure might require a full MAF assembly replacement. Check your specific application before ordering a standalone IAT sensor that does not exist for your vehicle.

When the IAT Is Built Into the MAF

Common vehicles with integrated IAT/MAF sensors:

• Most GM trucks and SUVs (2005+) — IAT is inside the MAF housing
• Ford F-150 (2004+) — integrated unit
• Toyota Camry, Corolla (2007+) — integrated unit
• Honda Accord, Civic (2006+) — integrated unit

If the IAT is integrated, you cannot replace just the IAT element. You are replacing the entire MAF/IAT assembly. Some aftermarket units separate the two, but OE replaces the whole unit. Budget accordingly.

Repair Costs