OBD codes / P0117
P0117
ModerateEngine Coolant Temperature (ECT) Sensor Circuit Low
P0117 is usually drivable short-term, but verify the engine isn't actually overheating — the gauge may read high because of the false signal. If the engine genuinely runs hot, treat that as urgent. Otherwise, get the sensor or wiring fixed soon; a false hot reading affects fueling and fan operation.
What this code means
The engine coolant temperature (ECT) sensor reports engine temperature to the computer. P0117 means that sensor's signal is reading low — which the computer interprets as extremely HOT (or a wire shorted to ground). It's the mirror of P0118. The usual cause is a failed sensor or a wire shorted to ground, occasionally a corroded connector. A false "hot" reading can lean out the fuel mixture, run the cooling fans constantly, or even push the car into a protective mode, so it's worth fixing rather than ignoring.
Symptoms you might notice
- Check-engine light
- Cooling fans running constantly
- Temperature gauge reading high when the engine isn't actually hot
- Possible rough running or reduced power
- Hard starting in some cases
What it costs to fix
Typical range: $40–$250 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| ECT sensor | $15–$80 | ~0.3–1 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
The sensor is inexpensive and usually easy to reach, so this is typically a low-cost repair. A wiring short can take a little longer to find but the parts are cheap.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0117 for my exact vehicle →
How to fix P0117
Easy — basic tools, most owners can do this
- Compare the reading to reality on a cold engine
After the car sits overnight, plug in a scan tool and read the coolant temperature before starting — it should match the outside air within a few degrees. A cold engine reporting something absurdly hot confirms the signal is lying, not the engine.
- Unplug the sensor and watch the reading flip
With the key on, disconnect the ECT sensor connector. An open circuit should snap the reading to the extreme cold end of the scale; if it stays pegged hot with the sensor unplugged, the wire is shorted to ground somewhere and the sensor is innocent.
- Inspect the wiring for a short to ground
Follow the sensor's two wires looking for insulation melted against a hot manifold, chafed through on a bracket, or pinched by a previous repair. Fix any damaged section — this is the cause when the unplug test stays hot.
- Replace the ECT sensor
If unplugging swung the reading, the sensor itself has shorted internally: the common outcome. Let the engine cool, release some cooling-system pressure, swap the sensor quickly to minimize coolant loss, and top up afterward.
- Clear the code and confirm normal behavior
Verify the temperature now reads sensibly from cold through full warm-up and that the cooling fans have stopped running constantly. That confirms the computer is no longer being told the engine is overheating.
DIY or shop? This is a genuinely beginner-friendly repair: the sensor is cheap, usually threads into an accessible spot on the engine, and the unplug test cleanly splits sensor faults from wiring faults with no special skills. Consider a shop only if the diagnosis lands on a short buried deep in the harness, since tracing that can eat time and benefits from a wiring diagram.
Tools for the DIY steps: OBD-II scan tool · Deep socket or wrench for the sensor · Small amount of matching coolant for top-up · Electrical tape or heat-shrink for wire repair · Drain pan
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0117.
Frequently asked
Can I drive with P0117?
Short-term usually yes, but first make sure the engine isn't truly overheating — the sensor may be falsely reading hot. If it's just the sensor, the car runs fine; fix it soon so fueling and fans behave normally.
What does "circuit low" mean for P0117?
The sensor's voltage is at the low end, which the computer reads as extremely hot or as a wire shorted to ground. That points to a failed sensor or a short rather than a real temperature.
Is P0117 the same as P0118?
Same sensor, opposite reading: P0117 reads too low (interpreted as hot/shorted), P0118 reads too high (interpreted as cold/open). Both are usually a sensor or wiring fix and are diagnosed the same way.
How much does it cost to fix P0117?
Usually inexpensive — the ECT sensor is cheap and easy to reach on most engines; a wiring repair is modest. Check the wiring before replacing the sensor.
Seeing P0117 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0117 for my vehicleSymptoms that trigger P0117
Drivers who get this code often notice one of these — each has its own likely-causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0117 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.