P0112 Code: Intake Air Temperature (IAT) Sensor Circuit Low Input

Quick answer

• What it means: The Powertrain Control Module (PCM) has detected that the voltage signal from the Intake Air Temperature (IAT) sensor is lower than the expected minimum threshold.
• Severity: Moderate. You can safely drive home or to a shop, but you should not ignore it for long.
• Most common cause: A failed IAT sensor or a short to ground in the IAT sensor wiring circuit.

What the P0112 code means

The official OBD-II definition for P0112 is "Intake Air Temperature (IAT) Sensor 1 Circuit Low Input."

To put it in plain English: your engine's computer needs to know how hot or cold the air entering the engine is. Cold air is denser than warm air, meaning it requires more fuel to maintain the perfect air-to-fuel ratio. The IAT sensor uses a thermistor (specifically, a Negative Temperature Coefficient or NTC thermistor) to measure this temperature.

As the air temperature goes up, the electrical resistance in the sensor drops, which lowers the voltage signal sent back to the PCM. A "Low Input" code means the voltage has dropped to near zero (typically below 0.2 volts). Because of how the thermistor works, a near-zero voltage tells the computer that the intake air is impossibly hot—often pegging the reading at 284°F to 300°F (140°C to 150°C). When the PCM sees this impossible reading, it triggers the check engine light and sets code P0112.

Common symptoms

When the PCM believes the engine is ingesting extremely hot air, it will lean out the air-to-fuel mixture. This causes several noticeable driveability issues:

• Illuminated Check Engine Light: This is usually the first and most obvious symptom.
• Poor fuel economy: The engine may struggle to run efficiently, forcing the PCM into a default "fail-safe" fuel mapping.
• Rough idling or hesitation: A lean condition can cause the engine to stumble, especially upon acceleration.
• Hard starting: Particularly when the engine is cold, since the computer thinks the air is already piping hot and doesn't provide the rich fuel mixture needed for a cold start.
• Engine pinging or knocking: A lean fuel mixture can cause pre-ignition, which sounds like a metallic rattling under load.

Common causes

Here are the most frequent culprits behind a P0112 code, ranked from most to least likely:

1. Faulty IAT sensor: The thermistor inside the sensor has failed internally and shorted out. (Note: On many modern vehicles, the IAT is integrated into the Mass Airflow (MAF) sensor).
2. Shorted wiring: A short to ground in the signal wire between the IAT sensor and the PCM (often caused by chafed wiring harnesses).
3. Corroded or damaged connector: Water intrusion, bent pins, or a melted connector can bridge the circuit and create a short.
4. Faulty PCM: Very rare, but an internal short in the engine computer can theoretically cause this issue.

How a technician diagnoses it

A master diagnostic technician won't just throw a sensor at the car. We use a systematic approach to prove exactly where the short is located:

1. Scan tool data and freeze frame: We hook up an OBD-II scanner and pull up the live data stream for the IAT sensor. If the code is active, the IAT reading will typically show a fixed value around 284°F to 300°F.
2. The disconnect test: With the scan tool still showing live data, we unplug the IAT sensor.
   • If the temperature reading instantly drops to -40°F (the default reading for an open circuit), the wiring is perfectly fine. The sensor itself is shorted internally and must be replaced.
   • If the reading stays pegged at 300°F even with the sensor unplugged, the sensor is not the problem. There is a short to ground in the wiring harness between the plug and the PCM.
3. Checking the 5-volt reference: Using a digital multimeter (DMM), we check the disconnected harness plug with the key ON, engine OFF. We should see a 5-volt reference signal from the PCM and a good ground. If the 5-volt wire reads 0 volts, it is shorted to ground somewhere in the harness.
4. Visual inspection: We trace the wiring harness back to the PCM, looking for chafed wires resting against metal brackets or the exhaust manifold.
5. Pinpoint resistance testing: If a wiring short is suspected, we disconnect the harness at the PCM and the sensor, checking for continuity to ground on the signal wire.

Typical repair cost

The cost to fix a P0112 code depends on whether the IAT sensor is a standalone unit, integrated into the MAF sensor, or if there is a wiring issue.

• Standalone IAT Sensor Replacement: Parts range from $20 to $50, with labor running about $50 to $100. Total: $70 to $150.
• Integrated MAF/IAT Sensor Replacement: If the IAT is built into the MAF sensor, the part is more expensive. Parts are typically $80 to $200, with labor around $50 to $100. Total: $130 to $300.
• Wiring repair: If the sensor is fine but a wire is shorted, there are no major part costs, but diagnostic and repair labor can take 1 to 2 hours. Total: $100 to $250.

Can I keep driving with this code?

Yes, you can safely drive your vehicle home or to a repair shop with a P0112 code. It is not an immediate emergency that will leave you stranded. However, you should not keep driving with it for weeks on end. Because the engine computer is receiving inaccurate temperature data, your vehicle will likely run lean, suffer from poor gas mileage, and could potentially fail an emissions test. Prolonged driving with a lean condition can also increase the risk of premature engine wear or catalytic converter damage.

Related codes

When dealing with a P0112, you might also see these related diagnostic trouble codes:

• P0111: Intake Air Temperature Sensor 1 Circuit Range/Performance (sensor reading is erratic).
• P0113: Intake Air Temperature Sensor 1 Circuit High Input (the exact opposite of P0112; usually an open circuit or unplugged sensor).
• P0114: Intake Air Temperature Sensor 1 Circuit Intermittent (loose connection).
• P0101 / P0102: Mass Airflow (MAF) Sensor codes, frequently seen together if the IAT and MAF are housed in the same unit.

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