Error Code P0110 is described as Intake Air Temperature (IAT) Circuit Malfunction. It’s actually a general trouble code for a problem on IAT electrical circuit sensor, as it sends incorrect voltage input signals to the PCM (Powertrain Control Module, or also known as ECU or Engine Control Unit), causing the latter to manage the fuel system incorrectly.

Definition

The IAT acts as a thermistor, meaning it measures the air temperature by reading the resistance in the air. It is located inside the Intake Manifold (or in the intake air ductwork) and it provides a crucial data that the PCM needs to control multiple things in the engine, from Air Fuel Ratio, Ignition Spark Timing and other important components of the Emission Control System. It usually comes with a two wire sensor supplied with 5V reference wire (also works as signal wire) from the PCM and the ground wire.

Resistance changes as air passes through the sensor. A change in resistance affects the 5V supplied to the sensor accordingly. Colder air will provide higher resistance and signal voltage, while warmer air offers lower in both resistance and signal voltage. The PCM monitors these changes in 5V and calculate the air temperature. If the PCM determines that the voltage is outside of its normal operating range, then it will trigger the Error Code P0110.

Common Symptoms

The most common tell-tale sign is the illumination of Check Engine light. It can also cause some drivability issues, such as:

  • Poor engine performance, poor idle
  • Erratic or hesitation upon acceleration
  • Running rich and backfires due to throttle position sensor and IAT sensor not being electrically synchronized together
  • Hard starting
  • Poor fuel economy

Possible Causes

The most common source of problems for this error code are the connector and wiring problems and damaged IAT sensor, sometimes it’s the PCM itself.

For connector and wiring problem, the wiring could be too close to components with higher voltage consumption, especially ignition wires or alternators, causing the wire’s voltage to fluctuate. Poor electrical ground can also contribute to the problem.

For the IAT sensor, it could be operating outside its specific operating range. Or it could be that there are damaged components inside.

Other possible causes include:

  • Open or Shorted to ground on signal circuit to IAT
  • Open in ground circuit to IAT
  • Poor connection at IAT (broken connectors, backed out terminals, etc)

How to Check

As with other error codes, P0110 is diagnosed using an OBD-II scanner. Qualified mechanic will reset the code then take the vehicle for a test drive and check whether the code comes back through its live feed. If the Check Engine light comes back, along with the error code, then that means error code is certain and needs a more thorough diagnosis to determine what really caused it.

With the key on and the engine off, the mechanic will have to check the IAT sensor connector. There should be a steady supply of 5V reference voltage and a good ground. The mechanic will then look for the proper engine performance wiring diagram to determine the right color and position of the connectors and wires to make sure nothing is loose or weak that causes bad temperature readings.

If the sensor input voltages to the ECU are incorrect, that would mean the IAT sensor has gone bad and needs replacement.

How to Fix

  1. Start by resetting the OBD-II code scanner, take the vehicle for a road test and see if it comes back.
  2. If the code comes back, check the voltage of the IAT sensor (normally at 5V) and the other electrical connectors and wiring. Disconnect all electrical connectors and reconnect them again to refresh the electrical connection.
  3. Check the voltage on IAT output on the sensor to see whether it increase from 0.5V to 5V as the intake and engine air temperature rises.
  4. If all the readings and wirings are in good condition, then you need to check whether the IAT sensor is defective and if it has incorrect or no output before you replace the MAP sensor.
  5. If everything seems good, your final test must be checking whether the PCM has gone bad.

Depending on the severity of the condition, the diagnosis and repair for error code P0110 can be meticulous, if not difficult, and would definitely require advanced tools and of course, skills. So if the problem persists despite of your diagnosis, then you should never hesitate to take your vehicle to your dealer or to a qualified mechanic.

This error code causes poor engine performance, and issues on the IAT sensor can result in excessive fuel consumption, low power, rough operation and hard starting in some cases. Continuous driving with this problem can cause serious internal damage to the engine.