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P0118 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


There are several things that you need to know about a P0118 trouble code. The first is that it is defined by or that it stands for that the engine coolant temperature circuit is experiencing high input.


Now that you have a better idea of what a P0118 trouble code is defined as, let’s take a deeper look at what trouble code P0118 means for a vehicle. This trouble code is the OBD-II generic code that indicates the ECM has seen the ECT sensor output go above 4.91 V or lower than -40°C (-40°F).


There are several key causes that can cause a P0118 trouble code to populate on your OBD-II scanner. The first is that your engine coolant level is low. This can also be caused by a faulty Engine Coolant Temperature (ECT) sensor or problems with the engine coolant thermostat. It also is not uncommon for this to be triggered by the sensor harness being open or shorted on the engine coolant temperature sensor. This may also be due to the fact that the electrical circuit for the ECT has a sensor poor connection.


There are several symptoms that the driver should experience or that the mechanic may notice when test driving the vehicle. You may notice the ECM will turn the check engine light on. In this case, the vehicle will go into failsafe mode, substituting input to 176 deg Fahrenheit. You may also notice that the engine may have a hard start when the engine is cold, but it should start normally when the engine is warm. The engine may run rough and hesitate until the engine gets warmer, but once it warms up it should run close to normal.


There are several steps that a skilled mechanic should follow when trying to accurately diagnose a P0118 trouble code.

First, you should inspect for damaged or disconnected sensor connectors. They should scan and document the codes received on their OBD-II scanner and view the freeze frame data to see when the code was set. Make sure you clear the OBD-II fault codes and retest the system to see if the code comes back Disconnect the sensor connector and be sure to inspect it for corrosion or any bent pins, and repair them as needed. You should connect the two connector pins together to see if the output on the scanner shows above 284 deg F. If it does, this would indicate the wiring is okay, but you should replace the ECT sensor. If after replacing the sensor it shows above 284 deg F, this means that the circuit has an open circuit in the wiring, connector or ECM and should be fixed by the technician

Common mistakes

If you follow the above steps for diagnosis and repair, you shouldn’t have an issue repairing the vehicle and resolving the code. However, there are some common mistakes that can be made when repairing this trouble code:

  • Not visually inspecting the problem area first
  • Not following the manufacturer’s pinpoint test procedure step-by-step, and skipping steps
  • Replacing the ECT sensor without knowing for sure that it is the problem
  • Not connecting it and viewing the ECM data to see if the temperature output from the sensor is as expected before the installation of the new ECT sensor

How serious is this?

The P0118 code will put the engine ECM to go into a failsafe mode, which may cause the engine to run rough, or hesitate until the engine warms up to its operating temperature.

The failsafe mode may also cause excessive fuel consumption, carbon fouling of engine components, and various drive complaints. This all, of course, depends on the manufacturer’s failsafe mode strategy. Driving a vehicle for an extended time with the vehicle in failsafe mode may require additional repairs to remove the excess buildup of carbon.

This may also lead to the need for repairing possible ignition problems in the future. This may also lead to the  continuous running of electrical cooling fans may run while the engine is on.

What repairs can fix the code?

There are a few simple, common repairs that will fix this trouble code:

  • Repairing or replacing the ECT connector.
  • Repairing or replacing the wiring open circuit as necessary.
  • Replacing the ECT with a new sensor.

Related codes

None listed.


Though a P0118 trouble code is not a complete detriment to operating your vehicle, it will cause your vehicle to run suboptimally. If this problem persists without proper diagnosis and repair, it can lead to further and more expensive repairs and maintenance of the vehicle.

P0118 Code – What Does It Mean & How To Fix It