P0115Powertrain
Powertrain · SAE
ECT Sensor — Circuit Fault
Meaning
The ECU has detected a problem in the engine coolant temperature (ECT) sensor circuit: the signal voltage is out of range (too high or too low) or the signal is absent. The fault prevents reliable coolant temperature measurement.
Common causes
- Faulty ECT sensor (resistance out of specification)
- Short to ground or to supply voltage in the ECT wiring
- Open circuit in the wiring or sensor connector
- Corroded or damaged connector
- Failed 5 V reference supply from the ECU
Symptoms
- Check-engine light (MIL) on
- Temperature gauge stuck at cold or pegged at hot
- Prolonged cold-enrichment fueling (engine never exits cold-start mode)
- Starting difficulty
- Possible continuous cooling fan operation
Severity
Moderate to high: without a valid ECT signal the ECU cannot correctly manage fuel mixture and ignition timing; overheating risk if the cooling fan fails to activate.
What to do
- Measure ECT signal voltage at the connector (0.5–4.5 V with a warm engine)
- Measure ECT sensor resistance and compare with the manufacturer's curve
- Check the wiring for shorts and open circuits
- Inspect and clean the connector
- Replace the ECT sensor if out of specification