P0118 Code: Coolant Temp Sensor High — Causes & Fix
P0118 means the engine coolant temperature (ECT) sensor signal is too high — the ECM reads an implausibly cold 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
Common causes are an open circuit in the ECT wiring, low coolant around the sensor, or a failed sensor. P0118 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
- Hard cold starts or rich running
- Temperature gauge reading low
How to fix it
- 1
Check coolant and connector
1. Confirm the coolant level so the sensor is submerged. 2. Reseat the connector and check for an open signal wire.
- 2
Test the sensor resistance
1. Compare resistance to the temperature chart. 2. Replace if open or out of spec, then clear the code.
Frequently asked questions
Can low coolant cause P0118?
Yes — if the sensor tip is not covered by coolant it reads cold. Top up and bleed the system before replacing parts.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.