What does it mean?
P1111 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: IAT Sensor Circuit High Input (Intermittent) .
Symptoms
- Check engine light that appears and clears again over several trips
- Intake air temperature in live data jumping to an extremely cold value for a moment
- Rich running with black smoke and a fuel smell during the fault
- Hesitation, a stumble or a brief surge while driving
- Hard starting when the fault happens at cranking
- Fuel consumption higher than the driver expects
Likely causes
- Loose or spread terminal in the IAT sensor connector that loses contact with vibration
- Broken strand inside the signal or ground wire that separates when the harness moves
- Sensor element that opens internally when it heats up
- Corrosion in the connector raising the resistance for short periods
- Harness chafing at a clip or bracket near the air intake
- Poor engine ground point serving the sensor return circuit
- Where the sensor is built into the mass airflow unit, an internal fault in that unit
How to fix it
- Graph the intake air temperature during a road test and note the moments the value jumps
- After an overnight soak, compare intake air temperature with coolant temperature — they should be within a few degrees
- Wiggle the connector and loom with the ignition on while watching the value to reproduce the dropout
- Inspect the connector for spread terminals, corrosion and a broken latch; restore terminal tension
- Measure the sensor resistance cold and warm and compare it with the resistance table
- Voltage-drop test the ground wire and clean the ground point if needed
- Repair the wiring or replace the sensor, then confirm the reading is stable through a full drive cycle