P0118 – Meaning, Causes, Symptoms, & Fixes

Code P0118 Definition

Engine Coolant Temperature (ECT) Sensor Circuit has higher than normal voltage

What Does P0118 Mean?

The engine coolant temperature (ECT) sensor monitors the fluctuations in the temperature of the engine coolant. This data is sent to the ECM, which uses this data to regulate the air to fuel ratio, cooling fans, and ignition spark timing needed by the engine. Code P0118 is the result of the ECT sensor indicating a high voltage input from the coolant temperature circuit. (typically over 4.7V)

What Are the Symptoms of Code P0118?

• Check engine light
• Rough engine performance
• Poor idle quality
• Lower fuel economy

*No noticeable adverse conditions in some cases

What Is the Cause of Code P0118?

• Rusted/Dirty Engine Coolant
• Air Pocket in Coolant System
• Frayed ECT wiring
• Malfunctioning ECT Sensor
• Open ECT circuit
• Faulty ECM

How Serious Is Code P0118? – Severe

This trouble code will put your vehicle into a failsafe mode, which may cause your car’s engine to hesitate and run rough. Other characteristics of the failsafe mode may include lowered fuel economy, increased emissions, and other driving inconveniences. We recommend getting maintenance immediately as these conditions, if unattended for extended periods of time, may cause further damage to your vehicle.

Code P0118 Common Diagnosis Mistakes

Prematurely replacing the ECT sensor before attempting to visually inspect the connector and cooling system.

Tools Needed to Diagnose P0118:

• FIXD
• Digital Multimeter
• Hair Dryer

How To Diagnose P0118

Difficulty of Diagnosis and Repair – 2 out of 5

1. Check to see if there are any other codes along with P0118 and clear your Check Engine Light with FIXD.
2. Disconnect the ECT sensor and check the circuit wiring for fraying or disconnection.
3. Check cooling system for air pockets or dirty/rusty coolant. If you find either, flush and bleed coolant system.
4. If there is no disconnection in the wires and the coolant appears good and to not have any air pockets, remove the coolant temperature sensor and check the resistance of the sensor. Check out this video of how to check the ECT. At roughly 70 °F the resistance should be approximately 2.5kV. Use the hair dryer to increase the temperature of the sensor. As the temperature goes up the resistance should go down. Now remove the hair dryer and watch the resistance values. As the temperature goes down the resistance should up.
5. If your ECT did not meet the above criteria then the sensor is faulty and needs to be replaced.
6. If the sensor passes the above tests, then you may have a wiring concern or in very rare cases have a faulty ECM.
7. To check the wiring, check the resistance of the wires from the ECT sensor to the ECM. You should have continuity and low resistance. If the test shows an open circuit or high resistance, repair the wiring.
8. If the wiring checks ok you may want to consider replacing the ECM.

Estimated Cost of Repair

For error code P0118, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair. 

• Engine Coolant Temperature Sensor $140-$200
• Coolant Flush $100-$150
• Wiring repair/replacement $100-$1000
• ECM $1000-$1200