P11C9 Possible Causes
- Faulty Intake Air Temperature (IAT) sensor
- Intake Air Temperature (IAT) sensor harness is open or shorted
- Poor electrical connection in the Intake Air Temperature (IAT) sensor circuit
How is code P11C9 repaired?
Start by checking the “possible causes” listed above. Visually inspect the corresponding wiring harness and connectors. Look for damaged components and check for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Check Engine Light on (or service engine soon warning light)
P11C9 Meaning
The Intake Air Temperature (IAT) sensor is a temperature-sensitive variable resistor that measures the air temperature in the intake system. The sensor’s resistance will change depending on the air temperature. The higher the temperature, the lower the resistance. The Engine Control Module (ECM) provides a reference voltage and monitors the voltage drop between a fixed-value internal resistor and the sensor’s resistance. This is called a voltage divider circuit.
IAT sensor values are used by the ECM processor to help calculate idle speed, fuel mixture, and ignition timing.
Inaccurate IAT sensor voltages can affect pulse width, idle quality, and tailpipe emissions. Intermittent signals can cause hesitation, stumbling, and surging. If an IAT sensor failure accompanies an Engine Coolant Temperature (ECT) sensor failure, cooling fan operation may also be affected.
Some manufacturers integrate the Intake Air Temperature (IAT) sensor as part of the Mass Air Flow (MAF) sensor (air flow meter).