P0117 Code: Coolant Temp Sensor Low — Causes & Fix
P0117 means the engine coolant temperature (ECT) sensor signal is too low — the ECM reads an implausibly high temperature.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $20 – $200
- Time to fix
- 30 minutes – 2 hours
What it means
Usual causes are a short to ground in the ECT wiring, a failed sensor, or a connector fault. P0117 is a generic OBD-II powertrain code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer petrol car or light truck regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Cooling fans running constantly
- Possible lean running or reduced power
How to fix it
- 1
Inspect the ECT connector and wiring
1. Locate the ECT sensor in the coolant passage. 2. Reseat the connector and check for a shorted signal wire.
- 2
Test and replace the sensor
1. Measure the sensor resistance against the temperature chart. 2. Replace if out of spec, then clear the code.
Frequently asked questions
Why are my fans always on with P0117?
A low ECT signal reads as very hot, so the ECM runs the fans to protect the engine even when it is cold.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.