P0117: Engine Coolant Temperature Sensor Circuit Low
Key takeaways
- P0117 means the coolant temperature sensor's signal voltage is below its normal range, which the computer reads as an impossibly hot engine.
- The engine is usually not actually overheating; the fault is almost always the sensor, its connector or its wiring.
- While the code is set, the cooling fan may run all the time and the engine may run rich, start hard or use more fuel, because the computer is working from a substitute value.
- Check the connector and wiring before buying a sensor; the sensor itself is $80–$250 installed on most cars.
- Ford bulletins for 2.7L and 3.0L EcoBoost engines trace P0117 and its sister codes to the sensor connector, its wiring or the sensor itself.
What P0117 means
Your engine computer is getting a coolant temperature signal so low it would mean the engine is far hotter than any running engine gets, so it has decided the signal can’t be trusted. The scanner name is Engine Coolant Temperature Sensor Circuit Low. The coolant temperature sensor is a thermistor: its resistance drops as coolant heats up, which pulls the signal voltage down. When that voltage sits below the bottom of its normal range, the computer sets P0117. In practice that almost always means a short to ground in the sensor or its wiring, not a real reading.
Is it safe to drive?
Yes, in most cases, while you get it fixed. Once the code sets, the computer ignores the sensor and uses a substitute value. Most cars turn the cooling fan on full-time as a precaution. Depending on how your car fills in the missing reading, the engine may run rich, start hard when cold, idle high, or use noticeably more fuel. The dashboard temperature gauge may read pegged hot or drop to cold if it uses the same sensor. What changes the answer: real overheating signs, such as steam, coolant boiling over, a sweet smell, or the heater blowing cold. Then it’s not the sensor. Stop and let it cool, and read car overheating.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Sensor connector damaged, corroded or not fully seated | Code clears or changes when the connector is wiggled; coolant or corrosion in the plug | $100–$250 |
| Sensor shorted internally | Unplug it: reading jumps to very cold (P0118) and P0117 stops; resistance far below spec | $80–$250 |
| Signal wire chafed and shorted to ground | Reading stays hot with the sensor unplugged; harness rubbed through on a bracket or cylinder head | $100–$600 |
| Sensor or harness design issue (some makes) | A bulletin for your exact model and year names P0117 | $80–$600, often covered by the bulletin |
What to check first
- Confirm the engine isn’t really hot. Check the coolant level with the engine cold and compare the scan tool temperature with a quick infrared thermometer reading at the thermostat housing.
- Look at the scan tool reading. A value pinned at the top of the scale (often around 280–300°F or higher) on a cold engine confirms a false signal.
- Unplug the sensor and watch the reading. If it drops to very cold, the sensor is shorted. If it stays hot, the wiring is shorted to ground.
- Inspect the connector and harness for coolant intrusion, corrosion, a loose lock tab, or insulation rubbed through near the engine.
- Look up bulletins. Ford and Lincoln bulletins for 2015–2020 2.7L EcoBoost engines (F-150, Edge, Fusion, MKX, Nautilus, Continental) and 2020 Explorer and Aviator trace P0117 and related codes to an unseated connector, damaged wiring, or the sensor, and one F-150 fix relocates the sensor with a jumper harness. A 2019–2020 Silverado and Sierra bulletin describes an engine harness shorting at the left cylinder head.
- Clear the code and drive after any connector repair; it should stay off once the circuit is sound.
What it costs
The cheap outcome is a connector repair, $100–$250. The common outcome is a new coolant temperature sensor at $80–$250 installed on most cars; some are buried under intake parts and sit at the top of that range. The expensive outcome is a shorted section of engine harness, up to about $600. Unplugging the sensor during a $100–$180 diagnosis tells a shop in seconds whether you need the sensor or the wiring.
Related codes
P0117 sometimes appears with P0118 (the same circuit reading high), P0116 and P0119 (range and intermittent faults on the same sensor), or P0128 (engine slow to warm up). A real overheat sets P0217 instead. If the gauge also climbs at stoplights, see car overheating at idle.
What owners report to NHTSA
5 complaints filed with NHTSA mention P0117, 5 of them since 2015, across 5 different models. The component owners most often filed it under: engine.
Manufacturer service bulletins that name P0117
23 technical service bulletins and manufacturer communications filed with NHTSA mention P0117, from 5 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- VOLKSWAGEN ATLAS (2020, 2021, 2022, 2018), bulletin 10218956: Customer states rattle noise from the underbody heat shields Customer states MIL-on, fault P0442 and/or P0456 stored in ECM memory Customer states rattle noise under vehicle Customer states MIL-on, fault P0463 stored in …
- VOLKSWAGEN ATLAS CROSS SPORT (2020, 2021, 2022), bulletin 10218612: Customer states rattle noise from the underbody heat shields Customer states brake noise, dust and uneven pad wear Customer states MIL-on, fault P0442 and/or P0456 stored in ECM memory Customer states rattle noise under …
- CHEVROLET SILVERADO 1500 (2019, 2020), bulletin 10176304: This Preliminary information communicates an issue with the engine wiring harness shorting at the left front cylinder head causing any of the following issues: -IPC gauges sweeping while driving -Several IPC warning mess…
- GMC SIERRA 1500 (2019, 2020), bulletin 10176304: This Preliminary information communicates an issue with the engine wiring harness shorting at the left front cylinder head causing any of the following issues: -IPC gauges sweeping while driving -Several IPC warning mess…
- FORD EXPLORER (2020), bulletin 10177711: Some 2020 Explorer/Aviator vehicles equipped with a 3.0L EcoBoost engine may exhibit an illuminated malfunction indicator lamp (MIL) and/or Engine Coolant Over Temperature warning with diagnostic trouble codes (DTCs) P01…
- LINCOLN AVIATOR (2020), bulletin 10177711: Some 2020 Explorer/Aviator vehicles equipped with a 3.0L EcoBoost engine may exhibit an illuminated malfunction indicator lamp (MIL) and/or Engine Coolant Over Temperature warning with diagnostic trouble codes (DTCs) P01…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Is my engine really overheating if I have P0117?
Usually not. P0117 means the sensor signal is lower than any real engine should produce, which points to a shorted sensor or wire. Check the coolant level when cold and watch for steam or a sweet smell; if those are normal, the reading is almost certainly false.
Why is my radiator fan running all the time with P0117?
Because the computer can't trust the temperature reading, most cars switch the cooling fan on as a precaution. It's protecting the engine. The fan should go back to normal once the sensor circuit is fixed.
Can P0117 make the engine run rich?
It can. With the sensor ignored, the computer fuels from a substitute value, which on many cars means extra fuel. You may notice worse mileage, a fuel smell or a rough, slow cold start. Get it fixed before the extra fuel reaches the catalytic converter for weeks.
What's the difference between P0117 and P0118?
They're opposite ends of the same circuit. P0117 means the signal is too low (reads very hot), usually a short to ground. P0118 means it's too high (reads very cold), usually an open circuit or unplugged sensor.
How much does it cost to fix P0117?
A connector repair is $100–$250, a new sensor $80–$250, and a shorted section of engine harness up to about $600 at an independent shop.