P0118 on GMC: How to Diagnose & Fix
Engine Coolant Temperature Sensor Circuit High
1 GMC model · 1 documented issue · $120-$450 repair
P0118 on GMC by model: symptoms, diagnosis and fix
A worn or leaking factory thermostat that stays open (plus a failing engine coolant temperature sensor) prevents the engine from reaching normal operating temperature. The ECM interprets the low/erratic reading as a sensor fault and enters a protective fail-safe mode: the electric cooling fans run at full speed continuously, the temperature gauge may drop to zero or read erratically, the A/C compressor may be disabled, and fuel economy suffers. It is a common and well-documented complaint across 2015-2019 5.3L/6.2L trucks and SUVs.
Common Symptoms
- Cooling fans running at full speed constantly
- Temperature gauge reads zero or fluctuates
- A/C compressor won't engage / no cold air
- Engine slow to warm up in cold weather
- Reduced fuel economy, check-engine light
How to Fix
Diagnose whether the thermostat is stuck open or the ECT sensor has drifted. The usual repair is replacing the integrated thermostat housing and the engine coolant temperature sensor (GM Genuine ECT sensor 12608814) together with fresh DEXCOOL. Clearing the codes and confirming the engine reaches ~210F resolves the fans-on-full and disabled-A/C behavior. Address it promptly because the fail-safe also cuts A/C and hurts mileage.
Sources for this issue (1)
P0118 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0118 mean on a GMC?
P0118 stands for "Engine Coolant Temperature Sensor Circuit High." P0118 indicates the engine coolant temperature (ECT) sensor circuit is reading abnormally high voltage, which the computer interprets as an implausibly cold coolant temperature. The ECT sensor changes resistance with temperature and tells the PCM how hot the engine is so it can manage fuel, the cooling fans, and the gauge. High voltage on this circuit usually points to an open circuit or a sensor reporting an unrealistically low temperature. The car may run rich, struggle to enter closed-loop operation, idle poorly, or show an inaccurate temperature gauge. On GMC it is documented across 1 model: Yukon.
What are the most common causes of P0118?
The most common causes of P0118 are: Faulty (open) engine coolant temperature sensor, Open or broken wire in the ECT signal circuit, Loose, corroded, or disconnected sensor connector, Poor ground or open in the sensor return circuit, Damaged wiring harness near the sensor, Corrosion in the connector terminals, Failed PCM input (rare). The specific cause varies by vehicle.
How much does it cost to fix P0118 on a GMC?
Published repair estimates on GMC range from $120 to $450 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0118 on a different make?
View P0118 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.