Air & Fuel Mixture ControlOBD2 Codes

P0118 – Meaning, Causes, Symptoms, & Fixes

What Does Code P0118 Mean?

  • P0118 definition: H02S2 Heater Control Circuit Low (Bank 2, Sensor 2)
  • Issue Severity: SERIOUS – Stop driving immediately
  • Repair Urgency: Fix this code immediately to avoid serious engine damage.
  • Diagnosis: 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.

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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).

P0118 Causes

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

P0118 Symptoms*

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

*No noticeable adverse conditions in some cases

How Do I Fix Code P0118?

With a P0118 code, the first step is to get it properly diagnosed to figure out what is causing the malfunction in the engine coolant temperature sensor circuit. Using the live data function of the FIXD sensor and app allows you to read and analyze engine data to properly diagnose a P0118 code.

If the sensors are all reading correctly and you’re not comfortable further diagnosing this issue at home, we recommend finding a RepairPal-certified shop to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

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How Much Does It Cost to Fix Code P0118?

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0118 code.

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Possible Repair Costs for P0118

When it comes to making repairs associated with the P0118 code, 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

DIY Steps to Diagnose Code P0118

If you’d like to try to fix code P0118 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Complete diagnosis may require some specialized equipment beyond what the FIXD Sensor can provide, but for the most part, this diagnosis and repair can be attempted by beginner DIYers. 

DIY difficulty level: Beginner

This repair can be attempted by beginner DIYers.

Tools/parts needed (our top picks from Amazon):

  • FIXD
  • Digital Multimeter
  • Hair Dryer

Scan your vehicle to verify P0118 is the only code present. If other codes are present, they must be addressed first.


Check cooling system for air pockets or dirty/rusty coolant. If you find either, flush, and bleed coolant system.


Disconnect the ECT sensor and check the circuit wiring for fraying or disconnection. 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.


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. 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.


If your ECT did not meet the above criteria then the sensor is faulty and needs to be replaced. If the sensor passes the above tests, then you may have a wiring concern or in very rare cases have a faulty ECM.

If at this point the vehicle is still setting the same code, you may have a more serious problem with your car’s oxygen sensor system, and you should bring the vehicle to a certified shop to have further diagnostic work performed.  

Common P0118 diagnosis mistakes

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

Still Need Help Fixing Code P0118?

If you’ve followed the steps above and are still experiencing issues with the engine coolant temp sensor and code P0118, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you to get the right repairs at a fair price.


Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

Jeffrey N. Ross
Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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  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

    2. I would replace both the upper and lower Coolant Temperature Sensors! There are not very expensive or difficult. Watch Youtube video ! The lower sensor controls the Fan operation. Turn Fan on when temp in radiator reaches a certain temp. Upper sensor is extremely important for the ECU telling how much Fuel/Air to send to injectors! These cheap sensors do for sure fail. And easily forgotten and not replaced as they should be!!!! Dont forget to let engine run till it really gets warm with radiator cap open, continue to add proper fluid mix as needed till air leaves system. Use Temp Gun and aim at lower and upper radiator hoses.
      Monitor temps, will take awhile before lower gets hot, but eventually fan/fans should kick on! Also watch car temp display that it is in normal range!!!!!!

  5. Turn off ac bob lol

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

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