P0118 – Meaning, Causes, Symptoms, & Fixes

Code P0118 Definition

Engine Coolant Temperature (ECT) Sensor Circuit High Open Problem

What Does P0118 Mean?

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

P0118 Symptoms*

  • Check engine light
  • Rough engine performance
  • Lower fuel economy

*No noticeable adverse conditions in some cases

P0118 Cause

  • Rusted Engine Coolant
  • Frayed ECT wiring
  • Malfunctioning ECT Sensor
  • Open in ground circuit of ECT sensor
  • Faulty ECM

Code P0118 Severity – Severe

This trouble code will put your vehicle into a failsafe mode, which may cause your car’s engine to hesitate and run rough until the engine reaches optimal operating temperature. 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 surrounding wiring, as it is often the cooling system that is the primary source of the issue.

P0118 Diagnosis

  • Tools Needed to Diagnose:

Difficulty of Diagnosis and Repair

  1. Check to see if there are any other codes along with P0118 and clear your Check Engine Light with FIXD.
  2. Check the freeze frame data for the ECT sensor to pinpoint the issue.
  3. Disconnect the ECT sensor and check the circuit wiring for fraying or disconnection.
  4. If there is no disconnection in the wires, connect the two connector pins together and use scanning tool to check temperature.
  5. If the scanning tool shows a temperature above 284 degrees Fahrenheit, the circuit could have a short in the wiring, the connectors, or possibly a faulty ECT sensor.
  6. Consider replacing ECT sensor if the check-engine light persists.

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Comments 7

jill jerram

April 20, 2019

I’ve been to way too many sites that just blah-blah about stuff that you did not ask.thank god for a site that tells you all from cause to repair .now I just have to convince my husband that we need a fixd. you men …thank you Jill Jerram from the biggest little city, RENO NV.

Gary Kimzey

June 18, 2019

I replaced that sensor in conjunction with replacing radiator, water pump, hoses, serpentine belt, thermostat and thermostat housing. What can I do to clear that code?


June 30, 2019

disconnect negative battery terminal and reconnect

Joyce Donnelly

August 24, 2019

If your car is a Honda, check user manual. It says to press the reset button at bottom of gauge panel while turning on car. Then, count 3 to 10 seconds before letting the button up. Hope this helps? It worked for me.

Valentino Winans

July 21, 2019

In my case when my car reached operating temp and I turned it off it acted like it was flooded when I tried to start it again and wouldn’t start until it cooled down. Oh, and the temperature gauge didn’t work….

Steven spullburg

August 14, 2019

If your temp gauge didn’t work your radiator fan most likely didn’t turn on and your engine was getting to hot.

Bob Madderra

August 18, 2019

My car runs great going down the road with A/C on but when you stop and let it idle temp goes up until you turn A/C off then it cools down I have replaced waterpump thermostat belt radiator sensor and the fan twice what else can I do to fix it

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