Fault code P0115 – a step-by-step guide to diagnosing and fixing it

Error code P0115 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has detected a fault in the coolant temperature sensor circuit. This DTC P0115 indicates a problem with the engine coolant temperature (ECT) sensor or its wiring. For various manufacturers, this trouble code may also be referred to as "Engine Coolant Temperature Circuit Malfunction".

What causes can this error code have?

• Defective coolant temperature sensor (ECT sensor)
• Damaged or corroded wiring to the sensor
• Loose or dirty plug connections
• Short circuit in the sensor cable
• Defective engine control unit (ECU)
• Low coolant level
• Thermostat problems
• Interrupted ground connection

What symptoms occur in parallel with fault code P0115?

• Starting problems: The vehicle starts poorly, especially when the engine is cold
• Irregular idling: The engine runs erratically or stutters when idling
• Poor fuel efficiency: Increased fuel consumption due to incorrect mixture formation
• Radiator fan problems: Fan runs permanently or does not switch on
• Power loss: Reduced engine power, especially when the engine is cold
• Incorrect temperature display: Temperature display in the dashboard does not work correctly

How to fix the problem of fault code P0115?

• Repairing fault code P0115 requires a systematic diagnosis of the coolant temperature components.
• Replace the coolant temperature sensor: Locate the faulty ECT sensor and replace it with a new original part, draining the coolant and bleeding it after installation
• Check and repair wiring: Inspect all cables to the sensor for damage, corrosion or breaks and replace defective cables
• Clean plug connections: Disconnect sensor plug, clean contacts with contact spray and reconnect firmly
• Check the cooling system: Check coolant level, top up if necessary and check system for leaks
• Replace thermostat: In the event of thermostat-related temperature problems, replace the defective part with a new one
• Diagnose the engine control unit: Use professional diagnostic software to check the ECU for defects and repair or replace if necessary