CodeXOBD

P0117 — Engine Coolant Temperature Circuit Low Input

P0117 means the coolant temperature sensor signal is stuck low, which the module interprets as an extremely hot engine. A shorted sensor or wiring fault is the cause.

Moderate

The module believes the engine is overheating. It may run cooling fans constantly, alter fueling dramatically, and display a temperature gauge reading that does not match reality. This code will cause an emissions test failure.

$10–$50Parts, typical range
0.2–1 hLabour
estimateNot a quote · 2026 basis

What P0117 means

The engine coolant temperature sensor is a thermistor whose resistance changes with temperature. As temperature rises, resistance falls and the signal voltage drops. P0117 sets when the voltage drops below the minimum threshold, which the module reads as a temperature so high it cannot be real. This can cause the module to run extremely lean or rich, activate cooling fans permanently, or enter a protective mode.

Technical summary
SystemPowertrain — cooling and temperature
How engine temperature is heldThe thermostat blocks flow to the radiator until the engine is warm, then opens. The coolant temperature sensor is the module's only way to know the engine's temperature, and it commands the fan from that reading. Stuck open, the engine never warms; stuck closed, it overheats; and a sensor reading wrongly produces both symptoms without either being true.Enginemakes heatThermostatopens when warmRadiatorFanwhen stationaryThe temperature sensor is the module's only sense of heat — everything follows it

Symptoms you may notice

What causes P0117

ECT sensor shorted internally

Very likelylow costeasy

The thermistor has failed short-circuit, producing a very low resistance that the module reads as extreme heat.

Signal wire shorted to ground

Likelylow costeasy

Chafed wiring near the engine can contact ground, pulling the signal voltage to zero.

Connector damaged or corroded

Possiblelow costeasy

Corrosion or damage in the sensor connector can create a short or near-short condition.

How to diagnose it

1

Check the temperature gauge or live data

With the engine cold and the ignition on, check what temperature the module is reading. If it shows maximum temperature on a cold engine, the sensor circuit is shorted.

Tools: OBD-II scanner with live dataExpected: Ambient temperature on a cold engineIf it passes: Reading matches ambient. The fault may be intermittent.If it fails: Reading shows extreme heat on a cold engine. Continue to step 2.
2

Measure sensor resistance

Disconnect the ECT sensor and measure resistance. On a cold engine it should be high (2,000-4,000 ohms). If it reads near zero, the sensor is shorted.

Tools: MultimeterExpected: 2,000-4,000 ohms when coldIf it passes: Resistance is in range. Check the wiring for a short to ground.If it fails: Near-zero resistance — replace the sensor.
3

Check the wiring for a short to ground

With the sensor disconnected, measure resistance from the signal wire to ground at the harness side. There should be no continuity to ground. If there is, the wire is chafed and shorted somewhere along its run.

Tools: MultimeterIf it passes: No continuity to ground. The sensor was the fault.If it fails: Continuity to ground — trace the wire and repair the short.

Related codes

P0118P0125P0128

Common questions

Can I drive with P0117?

You can, but the module thinks the engine is extremely hot and may run the cooling fans constantly, alter fueling, or limit power. Fix it promptly — the sensor is cheap and easy to replace.

Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)

This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.