P0117 Engine Coolant Temperature Circuit Low

P0117 indicates a low engine-coolant-temperature circuit input. The module sees a voltage or signal condition lower than expected from the coolant temperature circuit.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not diagnose overheating or cooling-fan behavior until the coolant temperature signal itself is proven accurate.

Symptoms of P0117

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0117

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Check coolant temperature live data against actual engine temperature and cold-soak ambient conditions.
Inspect sensor wiring for short-to-ground, connector corrosion, coolant contamination, and damaged insulation.
Review fan operation, enrichment behavior, and temperature gauge behavior to see whether the signal fault is affecting strategy.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.