P0111 – Intake air temperature (IAT) sensor -range/performance problem

By Ti (Contact Me)
Last Updated 2016-06-02
Mechanical Engineer
CodeFault LocationProbable Cause
P0111 Intake air temperature (IAT) sensor""" range/performance problem
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IAT sensor

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Table of Contents

  1. What Does Code P0111 Mean?
  2. What are the common causes of code P0111 ?
  3. How do you troubleshoot code P0111 ?
  4. Get Help with P0111

What Does Code P0111 Mean?

The P0111 occurs when the PCM reads a signal in the IAT circuit which varies from expected values based on other sensor readings (such as the Engine Coolant Temperature sensor).  This is a distinct condition from related codes P0112 and P0113.  For these codes the PCM reads either a consistent high or low voltage in the IAT circuit.

See the IAT in depth article (P0112) for more background on the IAT sensor.

Note: A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors. The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with these codes, it is important to regard all sensors and components as part of the control circuit the code refers to.

What are the common causes of code P0111 ?

Depending on year, make, and model, DTC P0111 may have number of causes. Here are some of the most common.

  • Defective IAT Sensor – As with all solid-state components, the IAT sensor may cease to function properly, be it due to manufacturing processes or damage.
  • Contaminated Sensor – If the IAT sensor is especially dirty, such as due to a poorly-installed air filter or excessive positive crankcase ventilation (PCV) blow-by, the sensor may deteriorate or won’t react as fast to temperature changes. This type of failure would likely be accompanied by DTC P0110.
  • Improper Installation – The IAT sensor needs to be in the full flow of air into the engine intake. If the sensor is touching a metal surface, such as IAT sensors installed in the intake manifold, it could ruin the sensor or throw off its reaction to temperature changes.
  • Stored Vehicles – Stored vehicles are particularly susceptible to rodent damage. In building their nests and making room for runways, rodents may gnaw through wires, among other things, interrupting circuits critical to your engine’s operation.

Diagnosing DTC P0111 is not a particularly difficult task. The sensor itself is simple in operation, which makes its analysis easy. On the other hand, if you have to trace an open or short circuit in the wiring harness, this will take time and patience. Depending on year, make, and model, the IAT may be reasonably priced, less than $100 in many cases, but if it is part of the MAF sensor, this will increase the price significantly. Have a professional double check your work before you condemn the MAF/IAT. Similarly, if you have done all your checks and suspect the ECU may be at fault, have your work double checked by a professional, before you condemn an expensive ECU.

How do you troubleshoot code P0111 ?

This is a simple circuit, just two wires running from the ECU to the IAT sensor. If you have access to a scan tool, you can use it to read temperatures directly, otherwise you can use a DVOM (digital volt-ohm meter), thermometer, and a short pin, such as a thin wire or paper clip. A resistance table for your specific year, make, and model, will be especially helpful. You can often find these online, or perhaps if you ask your local trusted automobile technician.

  1. Sensor Check – With the key in the off position, disconnect the IAT sensor. With your DVOM set to Ohms Ω, measure the resistance across the terminals of the sensor.
    1. If you read an open circuit or short circuit (∞ Ω or 0.0 Ω), the sensor is at fault. Replace the sensor and you should be good to go.
    2. If you read resistance, check it against the temperature / resistance chart. If the engine is cold, then the IAT temperature / resistance should be fairly close to ambient temperature, which you can measure with a thermometer. If the resistance is correct at ambient temperature, you may still have a sensor problem. A sensor that reads properly at ambient temperature may go out of range at other temperatures. You can check for sensor problems by checking the resistance after you change its temperature, such as by putting it in a pot of boiling water or in the freezer.
  2. Circuit Check – If the sensor itself appears to be properly responding to temperature changes, then you can proceed with circuit checks.
    1. With KOEO (key on, engine off), disconnect the IAT sensor, and check for voltage in the connector.
      1. One of the wires should read 5 V reference. If you have no 5 V reference, you may have an open circuit or an ECU fault.
      2. The other wire should read 0 V. If you can properly identify the signal wire, check for resistance to ground, which should read 0.0 Ω. An open circuit likely means you have a wiring problem. On the other hand, 0.0 Ω could still indicate a short to ground.
    2. If there is no 5 V reference voltage, there could be an open circuit between the ECU and the sensor, a short circuit to ground, or the ECU itself may be at fault. If there is no signal voltage on the other line, then you could have a defective sensor, open circuit, or short to ground.
      1. At the ECU, check for reference and signal voltage. If there is no 5 V reference, the ECU may be at fault. If there is low or no signal voltage, check for corrosion or an open circuit in the wires to the IAT sensor.
      2. Turn the key to the off position, disconnect the ECU connector, and check for resistance. If the resistance reading is the same as the sensor check, then the ECU may be at fault. If you measure 0.0 Ω or ∞ Ω, check for open or short circuit in the wiring to the IAT sensor.
  • Disconnect the sensor and measure resistance again, it should now read as an open circuit, ∞ Ω. If you read any resistance at all, check for short circuits in the wiring to the IAT sensor.
  1. Install a short wire, in the IAT sensor connector, and check for resistance in the circuit.
    1. The proper reading should be 0.0 Ω. Any reading over 1 Ω could indicate corrosion or an open circuit.
    2. Check for resistance to ground. Any reading under 1,000 kΩ could indicate a short to ground in one of the wires to the IAT sensor.
  2. If you have access to a scan tool and live data, you can perform many of these checks simply by reading ECU IAT readings. With KOEO, read the temperature with the sensor connected, and then disconnected. If there is no change, you have a circuit problem. If there is a change, you have a sensor problem.

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