What Does P0111 Code Mean?
OBD-II Code P0111 is defined as a Intake Air Temperature Circuit Circuit Range/Performance Problem
The Intake Air Temperature Sensor measures the rise and fall of the air temperature inside the Intake Manifold. This provides critical data needed for the Powertrain Control Module (PCM) to control the Air Fuel Ratio, the Ignition Spark Timing and many components of the Emission Control Systems.
Code P0111 sets when there is erratic performance in the voltage signal to the PCM from the Intake Air Temperature Sensor Circuit or when the voltage signal goes outside the appropriate range when compared to the values of the Coolant Temperature Sensor.
P0111 Symptoms
- Check Engine Light will illuminate
- In some cases, the engine may be hard starting and/or get poor fuel economy
- Poor engine performance/hesitation on acceleration
Common Problems That Trigger the P0111 Code
- Defective Intake Air Temperature Sensor
- Dirty air filter
- Defective Mass Air Flow Sensor
- Faulty or corroded Intake Air Temperature Sensor wiring or connections
Common Misdiagnoses
- Intake Air Temperature Sensor is replaced when the real cause is a dirty air filter
- Intake Air Temperature Sensor is replaced when the real cause is a poor connection or chafed wiring
- Intake Air Temperature Sensor is replaced when the real problem is in the Mass Air Flow Sensor
Polluting Gases Expelled
- HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
- CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
- NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
P0111 Diagnostic Theory for Shops and Technicians
When diagnosing a P0111 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive while paying close attention to engine load, throttle position, RPM, and road speed on a data streaming scan tool. As you drive the vehicle, compare these values to the Intake Air Temperature Sensor PID or parameter ID. The Intake Air Temperature Sensor voltage values should rise and fall with changes in engine temperature. Compare the Intake Air Temperature or IAT readings to the Coolant Temperature Sensor readings, as they should move in tandem with each other. However, the Engine Coolant Temperature sensor will have a much higher temperature range.
Check the IAT sensor connector with the key on and the engine off. There needs to be a steady 5 volt reference voltage and a very good ground. Find and use the proper engine performance wiring diagram to discern the proper color and position of these wires in the connector.
It never hurts to do a key on-engine off voltage output test of the IAT sensor. Typically, I CAREFULLY use a heat gun to raise the temperature of the area around the sensor and study the change in values of the Intake Air Temperature. It's important to use the scan tool data stream as this will verify the IAT harness and connections.
