P0117Engine Coolant Temperature Sensor 1 Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- The engine coolant temperature sensor 1 is an NTC thermistor: the control module feeds 5 V through a resistor, and as the coolant warms the resistance and signal voltage fall. Its value drives cold-start enrichment, idle speed, ignition timing, the radiator fan and the release of closed-loop mixture control. Some Ford engines measure cylinder head temperature instead and calculate a coolant value from it. P0117 means the signal voltage is too low, so the sensor would report an implausibly hot engine (around 140–160 °C). Usual causes are a signal wire shorted to ground, coolant or moisture in the connector, or an internally shorted sensor. Limits: GM below 55 ohms, Ford petrol below 0.244 V for 5 s, Ford diesel below 0.10 V, Mitsubishi below 0.1 V for 2 s. Mitsubishi then calculates with 80 °C; GM/Saab switch the radiator fan on and the A/C compressor off. GM needs two trips. On Ford engines with a head temperature sensor the equivalent is P1290.
- What you may notice
- Check engine light on
- Radiator fan runs constantly
- Hard cold start (no enrichment, engine reported hot)
- Temperature gauge at hot end
- A/C may be switched off
- Likely causes
- LikelySignal wire shorted to ground (chafing, pinched harness)
- LikelySensor shorted internally or coolant inside the sensor
- PossibleMoisture or coolant in the connector
- RareEngine control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.