Fault code P0078 – a step-by-step guide to diagnosing and fixing it

Error code P0078 is displayed and the check engine light is on - what does this mean?

DTC P0078 is recognized by the OBD/EOBD system when a problem is detected with the Intake Air Temperature Sensor Circuit High. This error code occurs when the control unit measures too high a voltage at the IAT sensor, which indicates a defect in the sensor or the associated wiring.

What can cause this error code?

• Defective intake air temperature sensor (IAT sensor)
• Broken or damaged sensor cable
• Corroded or loose plug connections on the IAT sensor
• Short circuit in the sensor wiring to ground
• Defective engine control unit (ECU)
• Dirty or contaminated sensor
• Faulty ground connection in the sensor system

What symptoms occur in parallel with fault code P0078?

• Starting problems: The vehicle starts with difficulty or irregularly
• Unsteady idling: Engine runs unstable or stutters when idling
• Poor engine performance: Reduced power and sluggish acceleration
• Increased fuel consumption: Significantly higher fuel consumption than usual
• Black smoke: Black exhaust fumes from the exhaust pipe
• Check engine light: Permanently lit check engine light

How to fix the trouble code P0078 problem?

• Repairing trouble code P0078 requires a systematic diagnosis of the intake air temperature sensor components.
• Replace the intake air temperature sensor: Replace the defective IAT sensor with a new original part and check the function with a diagnostic device
• Repair sensor wiring: Check all cables to the IAT sensor for breaks or damage and repair or replace defective cables
• Clean plug connections: Clean the plug contacts on the sensor with contact spray and make sure the connections are securely seated
• Check the ground connection: Check the ground connection of the sensor system and clean or repair corroded ground points
• Clean the sensor: Remove dirt from the IAT sensor with a suitable sensor cleaner and then check the function