P0115 — Engine Coolant Temperature Circuit Malfunction

What it means

The control module has detected an electrical fault in the engine coolant temperature (ECT) sensor circuit. This sensor governs cold start enrichment, radiator fan operation and ignition timing. Consequences can be hard cold starting, a rich or lean mixture, permanently running or non-running cooling fans and, in the worst case, overheating.

Likely causes (most common first)

1. Faulty coolant temperature sensor
2. Damaged wiring or a corroded connector at the sensor
3. Open circuit or short in the harness to the control module
4. Low coolant level so the sensor is not immersed in liquid
5. Poor ground connection in the sensor circuit
6. Faulty engine control module (rare)

Can you drive with it?

You can drive short distances while watching the temperature gauge; stop at once if the engine overheats.