Air & Fuel Mixture ControlOBD2 Codes

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

You may also like


  1. 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.

  2. 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?

    1. disconnect negative battery terminal and reconnect

      1. So far so good. This site is excellent

        1. I checked the resistance of the sensor and it was 7.4 🙁 still had the one i replaced laying around it also read higher than 2.4kv. Does this mean they are bad? I’ve been fighting tooth and nail to diagnose a random overheating problem all summer. So maybe they are getting cooked? Just ordered a new pigtail. Now i have P0118 and P0117. How can it be high and low?

          1. Did you ever figure this out? I am getting both codes as well.

    2. 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.

  3. 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….

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

  4. 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

    1. Turning on your AC automatically engages the radiator fan. If you are overheating in idle when AC isnt on, odds are your fan is not turning on. If you already checked the ECT sensor and wires and its all good, you are probably looking at the fan control temp switch (Mine is item number 35879 just punch it into Amazon)

      1. Where the ECT sensor is located

  5. Turn off ac bob lol

    1. Trying to locate engine coolant temperature sensors on 07 Acura mdx?

Leave a reply

Your email address will not be published. Required fields are marked *