Intake Air Temperature Sensor 1 Circuit Low
The Powertrain Control Module (PCM) has detected an unexpectedly low voltage signal from the Intake Air Temperature (IAT) sensor 1 circuit. Because the sensor uses a negative temperature coefficient, this low voltage translates to an impossibly high intake air temperature reading, typically indicating a short circuit.
While the vehicle will usually still drive, the engine computer will substitute a default temperature value, leading to poor fuel economy and increased emissions. It should be diagnosed and repaired soon to restore proper engine performance and efficiency.
Common symptoms
- Illuminated Check Engine Light
- Decreased fuel economy
- Rough idling or engine hesitation
- Difficulty starting the engine when cold
- Strong exhaust smell due to rich running conditions
Likely causes
- Defective Intake Air Temperature (IAT) sensor (internal short)
- Short to ground in the IAT sensor wiring harness
- Damaged or melted IAT sensor connector
- Corrosion or debris bridging the connector terminals
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the IAT sensor, connector, and wiring harness.
Look for: Look for melted wires, rubbed through insulation, or a damaged connector that could cause a short to ground.
Connect an OBD-II scan tool and view live data for the IAT sensor.
Look for: Check if the IAT reading is stuck at an extremely high temperature (often 284°F to 300°F+), which confirms the low voltage/short circuit condition.
Disconnect the IAT sensor and observe the scan tool live data.
Look for: If the temperature reading drops to an extremely low value (like -40°F), the wiring and PCM are good, indicating the sensor itself is shorted.
Measure the internal resistance of the IAT sensor using a multimeter.
Look for: Compare the resistance reading to the manufacturer's temperature-resistance chart; near-zero resistance indicates an internally shorted sensor.
Test the IAT signal wire for a short to ground with the sensor and PCM disconnected.
Look for: Continuity between the signal wire and chassis ground indicates a short in the wiring harness that must be repaired.
This page explains the generic P0112 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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