Fault code P0117 – a step-by-step guide to diagnosing and fixing it

Error code P0117 is displayed and the check engine light is on - what does this mean?

DTC P0117 is triggered by the OBD system when the coolant temperature sensor (ECT) sends a signal to the engine control unit that is too low. This EOBD fault code indicates a problem with the coolant temperature circuit, which can affect engine performance and fuel consumption.

What can cause this fault code?

• Defective coolant temperature sensor (ECT sensor)
• Damaged or corroded cable connections to the sensor
• Short circuit in the sensor wiring
• Defective engine control unit (ECU)
• Low coolant level
• Defective thermostat
• Loose or corroded plug connections
• Interruption in the sensor circuit

What symptoms occur in parallel with fault code P0117?

• Starting problems: The vehicle is difficult to start or requires several attempts to start
• Increased fuel consumption: The engine runs continuously in cold running mode
• Poor engine performance: Reduced power and rough engine running
• Black smoke: Excessive soot formation in the exhaust gas
• Overheating: Engine quickly reaches high operating temperatures
• Irregular idling: Engine runs unevenly at idle speed

How can the problem with error code P0117 be rectified?

• The repair requires a systematic diagnosis of the coolant temperature system.
• Replace the coolant temperature sensor completely and apply sealant to the sensor thread
• Check the sensor wiring completely and replace damaged cables or plug connections
• Check coolant level and top up if necessary, at the same time check cooling system for leaks
• Replace thermostat if it is permanently open or closed
• Test the engine control unit and have it replaced by a specialist workshop if defective
• Flush and bleed the entire cooling system in the event of contamination or air bubbles