P0119: Engine Coolant Temperature Sensor 1 Circuit Intermittent/Erratic. Meaning, possible symptoms and checks before repair.
Meaning, symptoms, causes and checks
Coolant temperature sensor 1’s signal has interruptions or implausible jumps. Actual temperature cannot change instantly like an unstable electrical contact. The fault may occur only with vibration, heat or moisture.
Affected system: Powertrain
Symptoms
- Difficult starting or unusual idle, depending on the calculated temperature.
- Higher consumption, engine warning light or a fallback fan strategy, depending on the vehicle.
Possible causes
- Corroded connector, open/shorted wiring or a failed sensor.
- Incorrect reference or ground; for plausibility faults, check actual coolant level and warm-up.
What to check
- With the engine cold, check coolant level and leaks; do not open the cap while the system is hot.
- After a complete cold soak, compare ECT with intake air and ambient temperature, allowing for location and residual heat.
- Inspect sensor 1’s connector and harness; test signal, supply and ground with the exact engine wiring diagram.
- Log ECT and signal voltage while gently moving the harness; watch for jumps, including as the engine warms.
- After repair, clear codes and recheck ECT temperature under the original recorded conditions, following the manufacturer’s procedure.
Also written as: P0119-00, P011900, PO119 (some scan tools add the fault-type byte, e.g. -00).