P0118 on a GMC: Causes, Fixes & Repair Cost
🟠 Moderate severity · drivable
Safe to drive, but the engine may run rich and use more fuel until the sensor circuit is repaired.
What P0118 means on a GMC
On a GMC, P0118 means the engine coolant temperature (ECT) sensor is sending a high-voltage signal that the computer reads as the engine being very cold. GM engines use a two-wire ECT sensor near the thermostat, and an open circuit from a failed sensor, broken wire, or corroded connector is the usual cause. The computer then runs the engine rich as if it were cold.
Is P0118 common on GMCs?
P0118 is common on Sierra and Yukon models with higher mileage. Corroded connectors are a well-known weak spot on GM engines, and the sensor wiring can chafe against the engine over time.
Commonly reported on: Sierra, Yukon, Terrain, Acadia.
Symptoms
- Check engine light on
- Poor fuel economy
- Hard cold start
- Engine runs rich
Common causes
- most common: Faulty coolant temperature sensor
- common: Corroded or loose connector
- common: Open sensor signal wire
- less common: Wiring chafed near the engine
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the coolant temperature sensor | Yes | $20–50 |
| Clean or replace the corroded connector | Yes | $20–40 |
| Repair the sensor wiring | Mechanic | $50–150 |
Frequently asked questions
Other common GMC codes
P0118 on other brands
Looking for the full (non-brand-specific) guide? See the P0118 code page →
Browse all GMC codes: GMC hub →
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.