Error Code P0112: Intake Air Temperature Circuit Low Input

Error Code p0112 is defined as IAT (Intake Air Temperature) Sensor 1 Circuit Low. This means, there’s the PCM receives excessively low voltage from the IAT sensor, and usually caused by a failed IAT sensor or wiring issue.

It’s a generic trouble code applicable to any vehicle equipped with OBD-II, though specifications and repairs of course, vary from one make and/or model to another.

Definition

The job of the IAT sensor is to measure the temperature of air that gets into the engine. It is built into the MAF (mass airflow) sensor (or mounted to the air filter duct housing in some vehicles) and works by detecting the intake air temperature and transmits the information to the PCM (powertrain control module, also known as ECM or engine control module). It reads temperature through a thermistor, a component sensitive to changes in temperature. This thermistor is supplied with 5V as reference voltage from the PCM and a ground.

When the air that enters is cold, the resistance in thermistor will be high; the opposite goes when it’s warmer. Changes in resistances of the 5V reference from the PCM inform the PCM of the change in temperature of the incoming air. To keep the temperature from causing combustion problems, the intake air tubing should be intact, and allow the engine to “breathe” air supplied from the engine compartment.

Intake air temperature is important, as the higher the temperature, the higher the combustion temperatures, resulting to higher NOx (nitrogen oxides) emissions. If the incoming air is too high than its allowable range, when the engine is still relatively low, then it will trigger the error codeP0112.

Common Symptoms

Aside from the activation of Check Engine light and the PCM going to failsafe mode, there are no obvious drivability problems for this error code. Though the engine may be harder to start, and fuel mileage may suffer.

The most obvious symptom however, is black smoke coming out from the tailpipe on acceleration. Also, depending on the type of IAT failure, emission test will show higher level of NOx or the engine may ping under load.

Possible Causes

As said earlier, Error Code P0112 is usually caused by bad IAT sensor; it could be damaged, internally shorted or open. However, it can also be caused by a number of different factors, such as:

  • Open wire causing the absence of reference voltage for the IAT sensor
  • Corroded or faulty IAT sensor connectors or wiring
  • Excessively high intake air temperature
  • Damaged IAT connector
  • Short or ground on signal circuit
  • Dirty air filter
  • Defective MAF sensor
  • Bad PCM

How to Check

As with diagnosing other error codes, qualified mechanics start their diagnosis by recording the freeze frame rate data, and then duplicate the conditions when the code was set through a test drive. The mechanic will pay attention to engine load, RPM, throttle RPM and road speed through the live data streaming scan tool. He will compare the values to the IAT parameter ID while driving the vehicle, and compare the results to IAT voltages or readings to the readings from the Coolant Temperature sensor. These two should move in tandem with each other, with the Engine Coolant Temperature having a higher temperature range.

At cold engine, the IAT should roughly match the reading from the coolant, as both will reach their ambient temperature. If the reading from the IAT is excessively high, then the mechanic will test the IAT connector for damage. If there’s none, the IAT sensor will be unplugged and plugged again to refresh the electrical connection. This should now show a minimum, around -20˚. If it doesn’t, then that means the IAT sensor is damaged and must be replaced.

If the reading is still high, that means the sensor must be unplugged and checked for resistance through the two wiring harness terminals. Infinite resistance means the PCM is the defective one. For finite resistance, you need to inspect and repair short to ground on signal circuit.

You can also check the IAT sensor, with key on, engine off. There should be 5V reference voltage and a good ground. Check with the vehicle’s engine performance wiring diagram to be sure.

How to Fix

Error Code P0112 is a simple trouble code which requires simple steps to fix, such as:

  • Repair or replacement of the IAT connector
  • Repair or replacement of wiring
  • Replacement of IAT sensor

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