Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.
P0116: Engine coolant temperature circuit range/performance
The engine computer can see a coolant-temperature signal, but the reading is not changing in the expected way as the engine warms or cools.
What P0116 means
The engine computer can see a coolant-temperature signal, but the reading is not changing in the expected way as the engine warms or cools. The value may be stuck, slow to respond or inconsistent with other operating conditions. The code does not prove that the temperature sensor itself has failed.
Can I still drive?
Book diagnosis promptly. A short, gentle trip to a nearby garage may be reasonable only if the coolant level is correct when fully cold, the gauge remains normal, the heater behaves normally and there is no red temperature warning, steam, leak, misfire or power loss. Stop safely and switch off if the engine is overheating or losing coolant; continued driving can cause major engine damage.
Symptoms
- Engine-management light.
- Temperature gauge that rises slowly, moves erratically or does not settle normally.
- Cooling fan running unexpectedly.
- Difficult cold starting, raised idle, poorer fuel economy or rough running.
- Weak cabin heat if the thermostat is holding the engine too cool.
- No obvious symptom other than the warning light on some cars.
Common causes
- Coolant-temperature sensor that is biased, slow or intermittently faulty.
- Thermostat stuck open or otherwise not regulating temperature correctly.
- Low coolant or trapped air around the sensor.
- Corroded connector, damaged wiring or poor electrical earth.
- A control-unit fault is possible but uncommon and should not be assumed first.
Safe first checks
- With the engine completely cold, check the coolant level using the handbook procedure and look for visible leakage. Save all codes and freeze-frame data before clearing anything. If a scan tool shows live data, compare coolant temperature with the surrounding air before the first start, then check that the reading rises smoothly. With the ignition off, inspect the accessible sensor connector and loom for moisture, damage or looseness. Do not remove a hot pressure cap or bridge electrical terminals.
Typical UK fix cost
Approximately £90–£350, including initial diagnosis and a typical sensor, local connector/wiring repair or mainstream thermostat replacement. An integrated thermostat housing, difficult access, extensive loom damage or repairs following genuine overheating may cost considerably more. This is an editorial working range, not a quotation.
Related models
This is a generic OBD-II code used across many makes and models. The exact test thresholds, component layout and repair route vary by engine and manufacturer, so check vehicle-specific technical information before ordering parts.
Related fault codes
- P0113: Intake-air temperature sensor 1 circuit high input
- P0115: Engine coolant temperature sensor 1 circuit
- P0117: Engine coolant temperature circuit low input
- P0118: Engine coolant temperature circuit high input
Sources
- Toyota service information — P0116 monitor and diagnostic description
- HELLA Tech World — coolant-temperature sensor function and testing
- GOV.UK Highway Code, Annex 6 — vehicle breakdown and overheating precautions
- ClickMechanic — UK coolant-temperature sensor replacement guide
A diagnostic trouble code identifies a system or circuit to investigate. It does not prove that a named part has failed. Preserve freeze-frame data and seek a vehicle-specific diagnosis before clearing the code.