What it means
The module detects a low input from the engine coolant temperature sensor circuit. With a typical NTC sensor, this may correspond to an implausibly high temperature.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine coolant temperature sensor sends a signal to the control module for fueling, warm-up decisions, and cooling-fan control. P0117 sets when the ECT circuit input is lower than expected; with a typical NTC sensor, that can make the module interpret the coolant as much hotter than it is.
Common causes
Most likely first.
- Signal wire shorted to ground
- Sensor failed shorted internally
Symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Cabin heater weak or excessively hot
- Possible long warm-up time or hard cold start
How to diagnose it
- Check freeze-frame and ECT live data with the engine cold; an implausibly hot reading before startup supports a low-input fault.
- Inspect the ECT signal wire and connector for a short to ground, corrosion, coolant contamination, or damaged insulation.
- Check whether the cooling fan is running and compare the scan-tool temperature with the actual cold engine condition.
- Test the ECT signal circuit for a short to ground and check the sensor resistance against the manufacturer's specification.
- If wiring and sensor tests pass, check the circuit reference and ground connections using the manufacturer's wiring information.
Common fixes
- Repair a signal wire shorted to ground or damaged insulation in the ECT harness.
- Clean or replace a corroded or coolant-contaminated ECT connector.
- Replace the ECT sensor if it is internally shorted or out of specification.
- Restore a faulty circuit ground or reference connection identified during testing.
Can I keep driving?
Avoid driving if the temperature gauge is unreliable, the fan is not operating when needed, or the engine shows signs of overheating; stop safely if it gets hot. A false hot reading can disrupt fueling and fan control, and an undetected cooling problem can damage the engine.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.