What causes P0118 on a Chevy Silverado?

P0118 on a Chevy Silverado is most commonly caused by a failed Engine Coolant Temperature (ECT) sensor with an open internal circuit, a corroded or damaged ECT sensor connector, or a broken wire in the ECT sensor harness. The ECT sensor itself is the most common cause and is an inexpensive part.

How do I fix P0118 on my Silverado?

To fix P0118: first inspect the ECT sensor wiring and connector for damage or corrosion. Then test the sensor resistance with a multimeter — it should read 3,000–3,500 ohms at room temperature. If resistance is infinite or out of range, replace the ECT sensor. The repair takes about 15 minutes and costs under $25 in parts.

Is P0118 serious on a Chevy Silverado?

P0118 should be fixed promptly because a faulty ECT sensor causes the ECM to mismanage fuel delivery — typically running rich, which causes poor fuel economy, deposits, and potential catalytic converter damage over time. It's an inexpensive and quick repair that prevents downstream issues.

What is the difference between P0117 and P0118?

P0117 indicates the ECT sensor circuit voltage is too LOW (sensor shorted to ground, reading impossibly cold). P0118 indicates the ECT sensor circuit voltage is too HIGH (sensor open circuit or failed, reading impossibly hot). Both indicate ECT sensor failure but in opposite directions.

By FullSizeChevy.com

Published April 27, 2026 · Updated August 17, 2026 · How we source this

P0118 Chevy Silverado: Coolant Temp Sensor High Input Fix

P0118 on a Chevy Silverado means the ECM is receiving an abnormally high voltage signal from the Engine Coolant Temperature (ECT) sensor — indicating either a faulty sensor, a wiring problem, or an open circuit in the ECT sensor circuit. This is a common and inexpensive fix on 4.8L, 5.3L, and 6.0L Vortec trucks.

What P0118 Means

The ECT sensor is a variable-resistance thermistor that decreases resistance as temperature increases. The ECM reads the voltage across this sensor — high voltage means low resistance means high temperature (or an open circuit with no current path). P0118 is stored when the ECM sees excessively high voltage from the ECT sensor circuit, suggesting the sensor is reading an impossibly high temperature or has failed open.

Symptoms of P0118

With P0118 active: the temperature gauge may read maximum or fail to register at all, the engine may run rich (the ECM assumes a cold engine when the ECT is faulty and enriches the fuel mixture), fuel economy drops, and the engine may be hard to start when warm. The Check Engine light will be on.

Diagnosis and Testing

Test the ECT sensor with a multimeter: at room temperature (70°F), resistance should be approximately 3,000–3,500 ohms. At operating temperature (195°F), resistance should be approximately 175–225 ohms. If resistance is infinite (open circuit) or wildly off, replace the sensor. Also inspect the ECT connector and wiring for corrosion, damage, or loose contact — these are common issues on GMT800 trucks with age.

ECT Sensor Location on Vortec Trucks

On GMT800 and GMT900 4.8L/5.3L/6.0L trucks, the primary ECT sensor is located in the front of the intake manifold coolant passage, near the thermostat housing. A secondary coolant temperature sensor for the gauge cluster is located separately. Confirm you’re testing and replacing the ECM sensor (the one with the 2-wire connector going to the wiring harness) rather than the cluster sensor.

Repair Cost

ECT sensor replacement: $10–25 for a quality part (ACDelco or Delphi recommended). Coolant losses during replacement are minimal. This is a 15-minute DIY repair. Have a container ready to catch about half a cup of coolant when removing the sensor.

For related cooling system codes, see our P0128 thermostat diagnosis guide.

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