P0117
Engine Coolant Temperature Sensor 1 Circuit Low
Engine coolant temp sensor
Generic OBD-II
High
What it means
P0117 means the coolant temperature sensor signal is reading low voltage, which the ECM interprets as an implausibly high coolant temperature. It is almost always an electrical fault — a shorted signal wire or a failed sensor — rather than an actual overheat, and it can throw off fuelling and fan control.
High
Can I keep driving? The engine still runs, but a false hot reading can richen or lean the mixture, run the cooling fans constantly, and cause hard cold starts — get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Cooling fans running constantly or coming on early
- Hard starting or rough running when cold
- Worse fuel economy
Common causes
Most likely first
- Coolant temperature sensor signal wire shorted to ground (most common)Likely
- Failed coolant temperature sensor reading out of rangeCommon
- Corroded or damaged connector at the sensorCommon
- Chafed or pinched wiring in the sensor circuitLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read the live coolant temperature value — a P0117 typically shows an implausibly high reading or a pegged value.
- Inspect the sensor connector and wiring for corrosion, chafing, or a short to ground.
- Unplug the sensor and check whether the reading swings the other way; back-probe the signal and ground circuits against spec.
- Replace the coolant temperature sensor if the wiring is good, then clear and re-test.
- Only suspect the ECM after the sensor and wiring are confirmed good.
FAQ
Quick answers
Is it safe to drive with P0117?+
Short trips are usually fine, but the wrong temperature signal can hurt cold starting and fuel economy and keep the fans running, so fix it soon.
Can I just clear P0117?+
It will come straight back if the sensor or its wiring is shorted. Repair the circuit or replace the sensor first, then clear it.
Related codes
Often seen with P0117
Read & clear P0117 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX