Error Code P0111 is described as (IAT) Intake Air Temperature Malfunction. It refers to a problem on IAT circuit range or performance problem, which is usually caused by short or open circuit.


The IAT is actually a thermistor, which means it varies its resistance depending on the temperature of the engine air intake. Basically, it measures the rise and fall of air temperature in the Intake Manifold. This sends important data for the PCM (powertrain control module, or also called as ECM or ECU electronic control module and engine control unit, respectively, in some makes) to control both Air Fuel Ratio and Ignition Spark Timing, as well as other components of the Emission Control Systems.

The IAT is usually a two-wire sensor, where one is supplied with 5V from the PCM and the other for ground. Changes in the 5V will determine the air temperature. If the intake air is cold, both resistance and signal voltage will be high. When the air is warm, resistance will be low, as well as the signal voltage.

Therefore, the Error Code P0111 is set when there is erratic voltage signal performance in the PCM from the Intake Air Temperature Sensor circuit, or if the voltage signal goes outside the set range relative to the values of the Coolant Temperature sensor. Or, if the PCM determines an abnormally larger change in an abnormally shorter time on the IAT signal circuit.

Common Symptoms

Obviously, this error code will activate the Check Engine light on the dashboard. In terms of drivability problems, issues may be hard to determine as they’re pretty common to other error codes. These symptoms include:

  • Hard starting
  • Poor engine performance
  • Hesitation on acceleration
  • Poor fuel economy
  • Black smoke from thee exhaust (in some cases)

Possible Causes

Potential causes for Error Code P0111 includes:

  • Defective IAT sensor
  • Open in signal or ground circuit
  • Short to ground in signal circuit
  • Dirty air filter
  • Defective MAF sensor
  • Poor connection at the PCM or at the sensor (faulty or corroded connections or wirings)

How to Check

As with other error codes, qualified mechanics diagnose P0111 by checking through a freeze frame data. They will then duplicate the conditions that set the code through a test drive and pay attention to engine load, RPM, throttle position, road speed, etc., and check the results through the data streaming scan tool and see if the code comes back.

The mechanic will also observe the live data for temperature output to see if it stays within its specifications. If there are no evident problems noted, then the technician will conduct a specific pinpoint test for this error code and do the needed repairs.

Vehicle owners can also conduct a key on, engine off voltage output test through the IAT sensor. A heat gun can be used to raise the temperature of the area surrounding he sensor and study the changes in values of the Intake Air Temperature. Again, scan tool data stream must be used in this test to verify the IAT connections and hardness.

How to Fix

Repairs for this error code are:

  • Repair or replace IAT sensor
  • Repair or replace faulty connectors or wirings
  • Move the sensor back into the air filter housing or the intake air tube
  • Replace the IAT sensor

Error Code P0111 is actually a pretty simple trouble code; simply look for extremely short changes that are extremely high in voltage. If the vehicle is really old, the harness is the usual cause of the problem. If not, then it’s the sensor that is the suspect for this code.

This trouble code puts the PCM to failsafe mode, which means, depending on the maker’s failsafe mode strategy, it may cause excessive fuel consumption, various drivability issues, and carbon fouling of engine components.

Driving with this problem for an extended period of time can cause further carbon or ignition problems, among others.