Draft guidance: awaiting Claude spot-check, qualified-mechanic review and named-editor approval. Do not use a fault code alone to replace parts.
P0117: Engine coolant temperature circuit low input
The engine computer is seeing voltage below the permitted range in the coolant-temperature circuit.
What P0117 means
The engine computer is seeing voltage below the permitted range in the coolant-temperature circuit. On the common negative-temperature-coefficient sensor design, this is normally interpreted as an implausibly hot reading. It often indicates a short to earth or a shorted sensor, but genuine overheating must still be ruled out.
Can I still drive?
Treat the displayed temperature as unreliable until checked. Consider only a short trip to a garage if the engine is clearly at a safe temperature, the coolant is at the correct level when cold, and there is no red warning, steam, leak, rough running or abnormal gauge movement. Stop immediately if there is any evidence of actual overheating.
Symptoms
- Engine-management light.
- Gauge or scan data suddenly showing an extremely high temperature.
- Cooling fan running continuously on some vehicles.
- Hard starting, rough idle, stalling or altered fuelling.
- Poor fuel economy.
- Few noticeable symptoms where the computer substitutes a default value.
Common causes
- Signal wire shorted to earth.
- Internally shorted coolant-temperature sensor.
- Coolant, water or corrosion inside the connector.
- Chafed, trapped or heat-damaged loom.
- Poor connection at the engine computer.
- Genuine extreme overheating in exceptional cases; control-unit failure rarely.
Safe first checks
- Check coolant level and leakage only when the engine is fully cold. Record codes and freeze-frame data, then compare cold-engine live coolant temperature with ambient temperature if suitable scan data is available. With the ignition off, inspect the plug and nearby wiring for moisture, bent pins, rubbing or melted insulation. Remember that “circuit low” refers to electrical voltage, not low coolant temperature.
Typical UK fix cost
Approximately £90–£250 for diagnosis and a typical sensor, connector or accessible wiring repair. Extensive harness work, control-unit testing or damage caused by real overheating sits outside this working range.
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
- P0115: Engine coolant temperature sensor 1 circuit
- P0116: Engine coolant temperature circuit range/performance
- P0118: Engine coolant temperature circuit high input
- P0120: Throttle/pedal position sensor or switch “A” circuit
Sources
- Toyota service information — P0117/P0118 circuit description and diagnostics
- HELLA Tech World — coolant-temperature sensor checks
- NRF technical article — coolant-temperature sensor operation and faults (PDF)
- ClickMechanic — UK diagnostic-inspection cost 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.