What causes fault code P0117?

• Most likely: Faulty Engine Coolant Temperature (ECT) sensor (internal short) • Likely: Short to ground in the signal wire circuit • Possible: Corroded or damaged ECT sensor connector pins • Rare: Internal ECM/PCM failure

How do you fix fault code P0117?

STEP 1: Inspect the ECT sensor connector for moisture or damage. Clean as necessary. STEP 2: Use a scan tool to monitor Live Data. If it reads 140°C+, unplug the sensor. If the value drops to -40°C, the sensor is faulty. If it remains high, the short is in the wiring. STEP 3: Check reference voltage at the connector with ignition ON. It should be 5V. STEP 4: Measure sensor resistance with a multimeter. At 20°C (68°F), it should be approx. 2k-3k Ohms; at 90°C (194°F) approx. 200-300 Ohms. STEP 5: Replace ECT sensor if resistance is out of spec.

Powertrain (Engine & Gearbox)Standard EOBD

P0117 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Low

Q: What are the symptoms of fault code P0117?

• Check engine light (MIL) illuminated • Engine cooling fans running continuously (failsafe mode) • Difficult to start when cold (ECM believes engine is already hot) • Poor fuel economy and rich exhaust (black smoke) • Temperature gauge stays at maximum or fluctuates erraticly

Last updated:1 February 2026

Related:Engine Coolant Temperature (ECT) Sensor, Engine Control Module (ECM), Wiring Harness, Cooling Fan Relay

System

Powertrain (Engine & Gearbox)

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Technical Description

P0117 is set when the Engine Control Module (ECM) detects an Engine Coolant Temperature (ECT) sensor signal voltage that is lower than the expected range. The ECT is an NTC sensor (Negative Temperature Coefficient), where resistance drops as temperature rises. A very low voltage (typically below 0.14V) is interpreted as an extremely high temperature (over 140°C/284°F), usually caused by a short to ground in the signal circuit or a failed sensor.

Possible Causes

Faulty Engine Coolant Temperature (ECT) sensor (internal short)

Short to ground in the signal wire circuit

Corroded or damaged ECT sensor connector pins

Internal ECM/PCM failure

Symptoms

Check engine light (MIL) illuminated

Engine cooling fans running continuously (failsafe mode)

Difficult to start when cold (ECM believes engine is already hot)

Poor fuel economy and rich exhaust (black smoke)

Temperature gauge stays at maximum or fluctuates erraticly

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P0117 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Low

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P0117 - Engine Coolant Temperature (ECT) Sensor 1 Circuit Low

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