P0112 – Intake Air Temperature (IAT) Sensor Circuit Low Input

The Diagnostic Trouble Code (DTC) P0112 indicates that the Engine Control Module (ECM/PCM) has detected a lower-than-expected voltage signal from the Intake Air Temperature (IAT) sensor. Since the IAT sensor is a negative temperature coefficient (NTC) thermistor, a low voltage usually indicates that the ECM interprets the intake air temperature as extremely high.

Symptoms

• Check Engine Light is illuminated.
• Hard starting.
• Rough idle.
• Poor engine performance.
• Reduced fuel economy.
• Engine hesitation during acceleration.
• Increased exhaust emissions.

Possible Causes

• Faulty IAT sensor.
• Short to ground in the signal circuit.
• Damaged wiring harness.
• Corroded or contaminated connector.
• Poor sensor insulation allowing moisture intrusion.
• ECM fault (rare).

Diagnostic Procedure

1. Read all stored and pending DTCs.
2. Inspect the IAT sensor connector and wiring.
3. Check for a short-to-ground condition.
4. Measure sensor resistance and compare it with specifications.
5. Verify the reference voltage and ground.
6. Compare live data with ambient air temperature.
7. Replace the sensor only after confirming failure.

Live Data Diagnosis (Autel Scanner)

Using an Autel scan tool:

1. Navigate to ECM → Live Data.
2. Select the IAT (°C or °F) parameter.
3. With the engine cold, the reading should be close to ambient temperature.
4. If the scan tool displays an extremely high temperature (often above 130°C or 266°F), inspect the sensor and wiring for a short to ground.
5. Compare the IAT value with the Engine Coolant Temperature (ECT) after the vehicle has been parked for several hours.

Typical IAT Signal Path

Intake Air
     │
     ▼
 IAT Sensor
     │
   Signal
     ▼
 ECM / PCM
     │
Fuel & Ignition Control

Note: Many vehicles integrate the IAT sensor into the MAF sensor. Wiring colors, terminal identification, and voltage specifications vary by manufacturer and model.

Smoke Test

A smoke test is generally not required for diagnosing DTC P0112 because this code is primarily caused by an electrical fault.

If an intake leak is suspected after the sensor, a smoke test may still be useful to rule out additional intake system problems.

Common Repairs

• Repair damaged wiring.
• Repair a short-to-ground condition.
• Clean or replace corroded connectors.
• Replace the faulty IAT sensor.
• Repair intake air leaks if necessary.

Important Note

P0112 commonly results from a short-to-ground in the sensor circuit or a failed IAT sensor. Always verify live data, resistance values, and circuit integrity before replacing the sensor.