Maintenance Tips, Tricks And Hacks For Your Vehicle

P0118 OBD-II Engine Coolant Temperature Sensor 1 Circuit High Trouble Code




The P0118 OBD-II trouble code means that there is a problem with the Engine Coolant Temperature (ECT) circuit and the sensor that goes with it. The ECT is a thermistor or an electrical resistor whose resistance is drastically decreased by heat. The ECT is placed in the coolant passage in the cylinder head of your engine.

In this article, I will be talking about the P0118 code, its symptoms, causes, and how to fix it.

What Does The P0118 Code Mean?

P0118 OBD-II Engine Coolant Temperature Sensor 1 Circuit High Trouble Code

The OBD-II generic code P0118 means that the Engine Control Module (ECM) saw that the ECT sensor output was greater than 4.91 volts or less than -40 degrees Fahrenheit.

The temperature of your car’s engine is read by a sensor inside the car. This information is sent to the ECM so that it can adjust the fans and other cooling devices as needed. A high input indicates that the engine is cool, whereas a low input indicates that the engine has warmed up.

The P0118 code can be made when your engine notices that the inputs are not reading their usual values or are outside the allowed range. At this point, the ECM usually defaults to a setting that cools the engine as much as possible to keep it from overheating.

(See also: P0171 OBD-II System Too Lean (Bank 1) Trouble Code)

Which Models Are Affected By The P0118 Code

MakeAffected By P0118 Code

What Are The Possible Causes of the P0118 Code?

The P0118 trouble code is caused when the vehicle’s computer detects that the engine coolant temperature sensor output is greater than 4.91 volts.

Below are all possible causes of the P0118 trouble code.

  • Rusted/dirty engine coolant
  • Air pocket in the coolant system
  • Frayed ECT wiring
  • Malfunctioning ECT sensor
  • Open ECT circuit
  • Faulty ECM

What Are The Common Symptoms of The P0118 Code?

If you have a P0018 code, you will likely not have a significant number of symptoms. Typically, the only sign of a problem will be a check engine light. Even though this is typically the case, it is not the only possible outcome.

Below, I’ve listed a few other potential symptoms.

  • Check engine light
  • Poor fuel economy
  • Rough engine performances
  • Hard starting

When a car’s engine fan and other cooling equipment run all the time, it causes the engine to work too hard. This means that the fuel efficiency will go down a little, but you probably won’t notice a big difference.

(See also: P0443 OBD-II Evaporative Emission System Purge Control Valve Circuit Trouble Code)

Is It Safe To Drive With a P0118 Code?

No, it’s not safe to drive with a P0118 code for extended periods because this code causes your vehicle to fall into failsafe mode.

Even though you might not notice anything strange while driving with a P0118 code, there are still some things that could go wrong. First, you are subjecting various components to additional wear.

Your engine fan isn’t meant to run all the time, and if you use it too much, it could wear out faster. And since your engine has no way of detecting when the coolant is becoming too hot, it can no longer shut down to protect itself while it’s overheating.

If you are driving with the trouble code P0118, you will likely not discover anything is amiss until something catastrophic occurs. And since a P0118 code is reasonably simple and inexpensive to repair, you shouldn’t risk your entire engine for a cheap repair.

How To Diagnose The P0118 Code

If you want to easily diagnose the P0118 trouble code, you should follow the steps below.

  1. Examine the sensor connectors for disconnection or damage.
  2. Scan and record the codes received and examined the freeze frame data to determine when the code was set.
  3. Clear the OBD-II trouble codes and test the system again to see if the problem is still there.
  4. Disconnect the sensor connector and inspect it for rust or bent pins, and make any necessary repairs.
  5. Connect the two connector pins to see if the output on the scanner is above 284 degrees Fahrenheit. If it is, this means that the wiring is in good shape, and the ECT sensor should be replaced.
  6. Above 284 degrees Fahrenheit, you will need to repair the open circuit in the wiring, connector, or ECM.

Most Common Mistakes When Diagnosing The P0118 Code

Here are the most common mistakes when diagnosing the P0118 code:

  • The problem area is not visually checked.
  • Not following the manufacturer’s precise test process step-by-step, and skipping steps.
  • Replacing the ECT sensor without being certain that it is the source of the issue.
  • Not connect it and look at the ECM data to see if the temperature output from the sensor is as expected, before installing the new ECT sensor.

How Much Does It Cost To Repair P0118 Code?

If you take your vehicle to a shop for diagnosis, most shops will start with an hour of “diagnosing time” (the time spent in labor diagnosing your specific issue).

This usually costs between $75 and $150, depending on the shop’s hourly rate. Many, if not most, shops will add this diagnosis fee to the cost of any repairs you need if you have them perform the repairs for you.

From there, a shop can give you a good estimate of how much it will cost to fix the P0118 code.

Here are the possible repair costs for the P0118 trouble code:

  • Engine coolant temperature sensor – $140-$200
  • Coolant flush – $100-$150
  • Repair or replacement the wiring open circuit – $100-$1000
  • ECM – $1000-$1200
MakeP0118 CodeRepair Cost
ToyotaYes$100 – $1200
NissanYes$100 – $1200
ChevroletYes$100 – $1200
BMWYes$100 – $1200
AudiYes$100 – $1200
BuickYes$100 – $1200
MercedesYes$100 – $1200
GMCYes$100 – $1200
SuzukiYes$100 – $1200
TataYes$100 – $1200
LexusYes$100 – $1200
MazdaYes$100 – $1200
MitsubishiYes$100 – $1200
KiaYes$100 – $1200
JeepYes$100 – $1200
FiatYes$100 – $1200
HondaYes$100 – $1200
HyundaiYes$100 – $1200
OpelYes$100 – $1200
FordYes$100 – $1200
FiatYes$100 – $1200
PeugeotYes$100 – $1200

What Repairs Can Fix The P0118 Code?

Repairs that can fix the P0118 code include the following:

  • Repairing or replacing the electronically controlled transmission (ECT) connector
  • Replacing the electronically controlled transmission with a new sensor
  • Repairing or replacing the wiring open circuit when it is necessary

How To Fix The P0118 Code

To fix the P0118 code, you need to:

  • Repairing or Replacing the ECT connector
  • Replacing ECT with a new sensor
  • Replacing the wiring open circuit when it is necessary

In Conclusion

The P0118 code should be taken seriously because it could cause your engine’s performance to significantly decrease.

This trouble code, most of the time, will put your car into failsafe mode, which can make the engine run rough or stall until it gets to the right temperature. Because of this failsafe mode, your car may use more gas than usual, and carbon may build up on engine parts.

This means that the P0118 code could be serious because, if it isn’t fixed, it could lead to other expensive problems.



Vide Polowenski, Senior Mechanic

The information in this article is current and up-to-date in accordance with the latest mechanic SOPs.

Please take the time to leave a comment if this article has helped you in any way, you need additional help, or you have a suggestion.

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