Intake Air Temperature Sensor Circuit Low Input
The P0112 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the Intake Air Temperature (IAT) sensor that is lower than the expected range (typically below 0.2 volts). This usually means the sensor is reading an extremely high temperature (e.g., over 300°F) or the circuit has a short to ground. The IAT sensor is a thermistor that changes resistance with temperature; low voltage suggests low resistance, often due to a short circuit, faulty sensor, or wiring issues. This can cause incorrect air-fuel mixture, leading to poor performance and increased emissions.
1. Most Common Causes
- Faulty Intake Air Temperature (IAT) sensor
- Short to ground in the IAT sensor signal circuit
- Open or shorted wiring in the IAT sensor harness
- Corroded or damaged IAT sensor connector
- ECM internal failure (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor engine performance, hesitation, or stalling
- Rough idle or hard starting
- Decreased fuel economy
- Black smoke from exhaust (rich condition)
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the P0112 code and check for any other related codes.
Step 2: Visually inspect the IAT sensor and its wiring for damage, corrosion, or loose connections.
Step 3: Disconnect the IAT sensor and measure its resistance with a multimeter; compare to manufacturer specs (typically 2-5 kΩ at 68°F).
Step 4: Check the voltage at the IAT sensor connector with the ignition on; should be around 5V reference. If low, check for shorts to ground.
Step 5: If sensor and wiring are good, test the ECM by backprobing the signal wire; if voltage is still low, replace the ECM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with P0112, as it can cause poor engine performance, reduced fuel economy, and potential damage to the catalytic converter due to a rich air-fuel mixture.
How much does it cost to fix?▼
The cost to fix P0112 typically ranges from $50 to $150, including parts (IAT sensor usually $20-$50) and labor. Diagnostic fees may add $50-$100.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.