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P0117: Engine Coolant Temperature (ECT) Circuit Low

Quick Answer

Safe to drive (short-term)

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.

Severity
Moderate · Cooling System
Estimated repair cost
From €12 to €190+, varies by vehicle

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What does P0117 mean?

P0117 is a cooling system-related diagnostic trouble code classified as moderate severity.

What are the symptoms of P0117?

  • 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

What causes P0117?

  • Coolant temperature sensor shorted internally (low resistance)

    : high

  • Signal wire shorted to ground

    : high

  • Corroded connector bridging the sensor terminals

    : medium

  • Chafed harness shorting the signal to chassis

    : medium

  • Wrong sensor fitted with incorrect resistance curve

    : low

  • ECU internal fault on the sensor input (rare)

    : low

Is it safe to drive with P0117?

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.

How do you diagnose 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

How much does P0117 cost to fix?

Repair Parts Cost Labor Cost Total Estimate DIY Difficulty
Replace coolant temperature sensor (DIY) €12–€45 €0–€0 €12–€45 Easy
Replace coolant temperature sensor (shop) €12–€45 €40–€100 €52–€145 Easy
Repair shorted wiring or connector €5–€30 €60–€160 €65–€190 Moderate
Diagnose short to ground (shop) €0–€0 €60–€120 €60–€120 Professional

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

P0117 on specific vehicles

Toyota

Toyota Corolla

2005-2024

On the Corolla, P0117 most often comes from a shorted sensor or moisture-induced corrosion bridging the connector terminals. The sensor is inexpensive and easy to reach, so confirm with live data and a resistance check before replacing.

Volkswagen

Volkswagen Golf

2005-2024

VW Golf combined coolant sensors can fail internally and short, producing a pinned-high reading. Connector and clip damage is also common on these sensors, so inspect the four-pin plug for moisture and a secure fit.

BMW

BMW 3 Series

2006-2024

On BMW 3 Series engines a shorted coolant sensor will trigger the cooling fan to run at full speed, which is often the owner's first clue. Connector fretting and harness chafing near the engine are worth inspecting before replacing the sensor.

Ford

Ford Focus

2005-2024

The Ford Focus can set P0117 from a shorted sensor or from a chafed harness near the engine, where insulation rubs through and grounds the signal wire. Inspect the pigtail for heat and abrasion damage before condemning the sensor.

Common questions about P0117

Why does P0117 make the gauge read hot when the engine is cold?
The coolant sensor is a thermistor whose resistance drops as it gets hotter, so a low signal voltage looks identical to a very hot engine. When the circuit shorts to ground, the voltage drops to near zero and the ECU interprets that as maximum temperature, even on a stone-cold engine.
Can I drive with P0117?
For short trips usually yes, but be careful. The ECU thinks the engine is overheating, so it may run the fan flat out and lean the mixture, hurting economy. The real danger is that a false high reading hides genuine overheating, so confirm actual temperature in live data and fix it soon.
Is P0117 the sensor or the wiring?
It can be either. A shorted thermistor inside the sensor is common and easy to confirm by unplugging the connector and checking whether the reading changes. If unplugging does not clear the implausible reading, suspect a signal wire shorted to ground in the harness.
How much does it cost to fix P0117?
If a shorted sensor is the cause, parts are usually 12 to 45 EUR and a DIY swap can be under 50 EUR. A shop sensor replacement runs roughly 60 to 150 EUR. Chasing a wiring short costs more because diagnostic labour is involved.

Read our detailed guides

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