Technical Description of OBD-II Trouble Code
The input from the Intake Air Temperature Sensor 1 Circuit is registering as low.
What does that signify?
This diagnostic trouble code (DTC) is a standard powertrain code that is applicable to vehicles equipped with OBD-II. While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The IAT (intake air temperature) sensor is responsible for measuring the temperature of the air entering the engine. The intake air temperature is crucial because higher intake air temperatures lead to higher combustion temperatures. Increased combustion temperatures result in higher emissions of Nox (Nitrogen oxides).
To prevent these higher temperatures from causing further combustion temperature increases, it is important for the intake air tubing to be intact, allowing the engine to receive air that is not sampled from the engine compartment. The IAT measures air temperature using a thermistor, which is supplied with a 5-volt reference voltage from the PCM (powertrain control module) and a ground. Typically, when the air temperature is cold, the resistance in the thermistor is high, and when the air temperature is warmer, the resistance decreases. This change in resistance alters the 5-volt reference from the PCM, providing information to the PCM about the temperature of the incoming air. If the PCM detects an unusually high incoming air temperature, such as 300 degrees, when the engine temperature is still relatively low, it will trigger a P0112 code.
Symptoms
There may not be any noticeable symptoms of a P0112 code other than the illumination of the Malfunction Indicator Lamp (MIL). However, an emissions test may reveal higher Nox readings depending on the type of IAT failure. Additionally, the engine may ping under load depending on the type of IAT failure.
Causes
Typically, a P0112 code is caused by a faulty IAT (internally shorted, open, or otherwise damaged). However, it could also be caused by:
Possible Solutions
Connect your scan tool or code reader to read the IAT reading. With a cold engine, the IAT reading should roughly match the coolant reading, as both will reflect the ambient temperature. If the IAT reading is excessively high, inspect the IAT connector for any damage. If no damage is found, unplug the IAT sensor and recheck the reading. It should now display the minimum temperature, around -20 degrees. If it does, then replace the IAT sensor. However, if the reading is still high, unplug the sensor and check for resistance across the two wiring harness terminals. If there is infinite resistance, then the PCM itself is faulty. If the resistance is not infinite, then investigate and repair the short to ground on the signal circuit.
Other DTCs related to the IAT sensor and circuit: P0095, P0096, P0097, P0098, P0099, P0110, P0111, P0113, P0114, P0127
