P0117Generic code

P0117 Code: Engine Coolant Temperature Circuit Low

The P0117 code means the ECT sensor signal is below its minimum value. On a thermistor, that means the computer reads an impossibly high temperature, almost always because of a short to ground.

Severity
Medium
Can I keep driving?
Yes, but with caution
Estimated cost
$15 to $250
Difficulty
Easy
System
Air and Fuel
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0117 code means

The engine coolant temperature (ECT) sensor sits in the cylinder head or in the thermostat housing, in contact with the coolant. The computer relies on it because it decides cold enrichment, idle speed, when to enter closed loop, the radiator fan and, on automatic transmissions, torque converter lockup.

The sensor is an NTC thermistor: its resistance drops as the temperature rises. The computer sends it 5 V and reads the resulting voltage. A signal below the minimum (normally less than 0.1 to 0.2 V) is the same as an impossibly high temperature, and that almost always means a short to ground: the signal wire touches metal, or the sensor is shorted inside. While the fault lasts, the computer believes the engine is hot: hard starting when cold, low idle, a lean mixture when cold, and the fan may run nonstop.

Remember that the P0117 code points to the circuit where the computer saw the anomaly, not necessarily the failed part. Check the wiring before you replace the sensor, and test the ECT sensor step by step as described below.

P0117 code symptoms

  • Check engine light on steadily.
  • The computer believes the engine is hot: hard starting when cold, low idle, a lean mixture when cold, and the fan may run nonstop.
  • Radiator fan running continuously.
  • Erratic temperature gauge on vehicles where the dash uses this sensor.
  • Companion codes for the same sensor may appear (low signal, high signal or intermittent).

Likely causes of the P0117 code

  1. Signal wire shorted to ground by rubbing against the engine or chassis, very common where the harness passes near metal brackets.
  2. Sensor shorted internally, with its resistance dropping to nearly zero ohms.
  3. Connector with water or corrosion that creates a path between pins.
  4. Complementary check: a low coolant level leaves the sensor surrounded by air and gives erratic readings, so top off and bleed the system before you diagnose.

How to diagnose the P0117 code step by step

  1. Read the sensor live data and compare it with what is expected. With a cold engine after a full night, the ECT should match the IAT. After starting, the temperature should climb steadily to 85 to 105 °C (185 to 221 °F).
  2. Inspect the connector. Unplug it, look for green, backed-out or oily pins, and plug it back in firmly.
  3. With the key on and the sensor unplugged, measure the reference at the connector. There should be about 5 V between the signal and ground.
  4. Jumper test. With the sensor unplugged, the scan tool should show about -40 °C (-40 °F). When you join the two connector pins with a wire, it should jump to more than 120 °C (248 °F). If it does, the wiring is fine and the problem is the sensor.
  5. Measure the sensor resistance and compare it with the technical data table at the current temperature.
  6. Do the wiggle test with the engine running. Move the harness and the connector while you watch the live data, because a jump shows you where the fault is.
  7. Check the continuity of each wire between the sensor connector and the computer connector with the key off.

How to fix the P0117 code

  • Find where the wire is rubbing against ground and repair the insulation.
  • If the code changes to high signal when you unplug the sensor, the sensor is shorted, so replace it.
  • Dry and clean the connector if it had water in it.
  • Use a quality original or equivalent sensor, because cheap generic ones often have different response curves.
  • Clear the codes, drive one full cycle and check in live data that the reading makes sense.

Technical reference data

  • Approximate resistance: about 2,500 ohms at 20 °C (68 °F) and 200 to 300 ohms at 90 °C (194 °F).
  • Approximate signal voltage: 3 to 3.5 V cold and 0.5 to 1 V with the engine hot.
  • Normal operating temperature: 85 to 105 °C (185 to 221 °F).
  • Open circuit on the scan tool: about -40 °C (-40 °F). Short to ground: more than 130 °C (266 °F).
  • Values are approximate, so check the manufacturer data for your engine.

Brand-specific notes

Many engines have two sensors: one for the computer and one for the dash gauge. A gauge that reads correctly does not rule out an ECT fault, which is worth remembering with any P0117 code.

P0117 on Renault

On some Renault engines the sensor is dual, with two signals in one body.

P0117 on Peugeot

On some Peugeot engines the sensor is dual, with two signals in one body.

P0117 on Volkswagen

On some Volkswagen engines the sensor is dual, with two signals in one body.

Frequently asked questions about P0117

Can I drive with a P0117 code?
With caution and only for a short time. The engine runs on substitute values, so it may lose power or use more fuel and, in some cases, go into limp mode.
Does the P0117 code always mean replacing the ECT sensor?
No. In most cases the fault is in the connector or the wiring. Do the power, ground and continuity tests first.
What is the difference between low signal and high signal?
On a thermistor, a low signal means an impossibly high temperature (a short circuit) and a high signal means an impossibly low temperature (an open circuit).
How much does it cost to fix P0117?
Roughly $15 to $250. The cheapest repair is fixing a connector and the most expensive is replacing the sensor with labor. It varies by shop and region.
What does the P0117 code mean?
It is a generic OBD2 code that means the engine coolant temperature sensor signal is too low. The computer reads an impossibly high temperature, which usually points to a short to ground.
What is the most common cause of P0117?
A signal wire rubbing against the engine or chassis and shorting to ground. A sensor shorted inside or a connector with water in it come next.

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