Technical Description of OBD-II Trouble Code
Range/Performance Issue with Intake Air Temperature (IAT) Sensor 1 Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although 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 a thermistor that changes its resistance based on the temperature of the engine intake air. It is usually a two-wire sensor, with one wire receiving 5 Volts from the PCM (Powertrain Control Module) and the other serving as the ground. The PCM monitors the change in the supplied 5 Volts to determine the air temperature. When the intake air is cold, the resistance is high, resulting in a high signal voltage.
When the intake air is warm, the resistance is low, resulting in a low signal voltage. This code indicates that the PCM detected a larger-than-normal change in a shorter-than-expected time on the IAT signal circuit.
Symptoms
Since this code is likely indicating an intermittent problem on the IAT circuit, there may not be any present symptoms. However, the MIL (Malfunction Indicator Lamp) will likely be illuminated. The vehicle may exhibit some drivability issues, but it is more probable that there will be no noticeable symptoms for the driver.
Causes
Possible causes of the P0111 DTC include:
Possible Solutions
If there are other IAT codes present, it is recommended to diagnose them first. If not, then using a scan tool, verify the IAT voltage with KOEO (Key on Engine Off).
If, on a cold engine, the reading is the same as the CTS (Coolant Temperature Sensor), then the problem is intermittent. However, if the IAT reading is different from the CTS, refer to the diagnostic procedure for P0110. If your scan tool has a freeze frame failure records feature, use it to determine the IAT reading at the time of the failure. If the reading indicates an extremely cold temperature (around negative 30 degrees F), it suggests an intermittent high resistance reading on the IAT signal circuit.
Check for an open ground on the ground circuit and signal circuit. If they are functioning properly, try artificially raising and lowering the temperature of the IAT sensor. This can be done by removing the IAT and subjecting it to freezing temperatures and then applying heat with a heat gun (taking care not to overheat the IAT and cause it to melt). Monitor the resistance change using an ohmmeter connected to each terminal. The resistance should vary smoothly without any sudden jumps. If the reading jumps suddenly, replace the IAT sensor.
However, if the freeze frame reading indicates the highest extreme temperature (above 250 deg. F), it suggests an intermittent low resistance on the signal circuit. Check for a short to ground on the signal circuit. If it appears to be fine, perform the artificial heat test mentioned above and replace the IAT as necessary. If the problem cannot be replicated, use a voltmeter to monitor the signal voltage while “wiggling” the wiring harness. Look for a sudden change in voltage, which indicates a short or open. Replace the IAT sensor as necessary.
This is a relatively simple code that primarily detects extremely short changes with relatively high voltage. In most cases, the faulty component is the sensor itself, unless the vehicle is very old, in which case there may be issues with the wiring harness.
Other IAT sensor and circuit related DTCs: P0095, P0096, P0097, P0098, P0099, P0110, P0112, P0113, P0114, P0127
