P0117: Engine Coolant Temperature (ECT) Circuit Low

P0117 means the engine coolant temperature (ECT) sensor circuit voltage is too low, which the ECU reads as an implausibly high temperature. Because the sensor is a thermistor whose resistance falls as it heats, a short to ground or a shorted sensor produces a low voltage that mimics extreme heat. The ECU often responds by running the cooling fan at full speed. Repair typically costs 40 to 180 EUR for a sensor or wiring fix.

P0117 is a cooling system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0117 and illuminates the check engine light.

If your vehicle has triggered P0117, you may notice one or more of these symptoms:

• Check engine light illuminated
• Temperature gauge reading very high or pinned
• Cooling fan running constantly at high speed
• Lean fuelling and possible hesitation
• Hard starting if the ECU thinks the engine is already hot
• Reduced fuel economy

Here are the most common causes of P0117, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. Usually safe to drive short distances. P0117 means the coolant sensor signal voltage is too low, which the ECU interprets as an implausibly hot engine (a low-resistance short reads as high temperature). This can force the cooling fan to run at full speed and lean out fuelling, hurting economy. Because the gauge may show a false high reading, confirm the real temperature in live data and fix the fault promptly so you do not mask genuine overheating.

Follow these steps to pinpoint the root cause of P0117:

1. Read the code and watch the live coolant temperature PID with Skanyx. P0117 typically shows the maximum value (often around 120 C or higher) even on a cold engine, which is a clear sign of a low-voltage short rather than a real overheat
2. Compare the live coolant reading against actual engine temperature by touching the upper radiator hose; if the engine is cold but the PID reads hot, the circuit is shorted
3. Unplug the sensor connector and check whether the reading drops to the open-circuit default; if it does, the sensor itself is likely shorted internally
4. Inspect the connector and harness for corrosion, moisture, or a chafe point shorting the signal wire to ground or to the sensor body
5. Measure the sensor resistance with a multimeter and compare to the manufacturer table; an abnormally low resistance confirms a failed sensor
6. If the sensor and connector are good, test the signal wire for a short to ground back toward the ECU

Repair costs for P0117 vary depending on the root cause and your vehicle. Here are typical estimates:

P0117 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0117 or indicate related issues: