What Does Code P0118 Mean? An Expert Guide to Diagnosing the Issue

Code P0118 is a generic trouble code that indicates a malfunction within the engine’s coolant temperature sensor circuit. The code is triggered when the Engine Control Module (ECM) detects an abnormally high voltage within the sensor circuit. It is important to note that this code is often associated with other codes, such as P0117 and P0116.

The coolant temperature sensor is responsible for monitoring the temperature of the engine’s coolant. It sends a signal to the ECM which adjusts various engine parameters in order to maintain optimal engine performance and fuel economy. When the sensor detects an abnormally high voltage, it triggers code P0118 and illuminates the Check Engine Light on your vehicle’s dashboard.

Common symptoms of this code include lack of power, reduced fuel economy, stalling, and hesitation when accelerating. Diagnosing this issue starts with visual inspection of all related components including wiring harnesses and connectors followed by testing the coolant temperature sensor itself with a multimeter. If not faulty, then further diagnosis may be needed in order to isolate any other potential issues that could be causing this trouble code to trigger.

What Does Code P0118 Mean?

Understanding Automobile Codes

Understanding the codes behind automobile systems can be a daunting task. The Diagnostic Trouble Codes (DTCs), more commonly known as automobile codes, are codes that are stored by the onboard computer of a vehicle upon detecting an issue with one of its systems. Common automotive diagnostic codes, such as code P0118, can help diagnose and repair problems with a vehicle’s system.

What is Code P0118?

Code P0118 is an OBD-II code triggered when a vehicle’s engine control module or powertrain control module detects an issue with the Engine Coolant Temperature (ECT) sensor circuit. This code is part of a larger set of codes that detect issues with the cooling system. In this case, code P0118 indicates that the ECT sensor input is higher than expected when compared to the readings from other sensors.

Diagnosing Code P0118

In order to diagnose code P0118, you will need a few tools and equipment. You will need an OBD-II scanner and some basic diagnostic tools such as wrenches and screwdrivers. Additionally, you may want to have some coolant on hand in case you need to top off your vehicle’s coolant levels. Here is a step-by-step guide for diagnosing code P0118:

  • Connect the OBD-II scanner to your vehicle.
  • Retrieve the trouble code from your vehicle’s onboard computer.
  • Check for any other trouble codes that may be present.
  • Check your vehicle’s coolant level.
  • If necessary, add coolant and recheck for any additional trouble codes.
  • If no additional trouble codes are present, inspect the wiring harness for any signs of corrosion or damage.
  • Inspect all electrical connectors connected to the ECT sensor circuit.
  • Test all circuits connected to the ECT sensor using an ohmmeter or multimeter.

If all tests come back good then it is likely that you have a faulty ECT sensor and it should be replaced.

Common Fixes for Code P0118

The most common fix for code P0118 is replacing the faulty ECT sensor. You can purchase an OE replacement from most auto parts stores or online retailers. Additionally, it is important to check your coolant level before replacing any parts as low coolant levels can trigger this code as well.

Preventing Code P0118 from Reoccurring

To prevent this code from reoccurring it is important to keep up with regular maintenance on your vehicle’s cooling system including changing out old coolants and flushing out any debris or contaminants in the system. Additionally, it is important to test your system periodically in order to catch any issues before they become major problems down the road.

What Does Code P0118 Mean?

Code P0118 is a generic diagnostic trouble code (DTC) associated with a vehicle’s engine control module (ECM). This code indicates that the ECM has detected an issue with the vehicle’s engine temperature sensor. This could mean that the sensor is malfunctioning, or that there may be a wiring issue somewhere in the system.


When code P0118 is triggered, it typically causes engine performance issues such as rough idling, misfiring, stalling, and poor fuel economy. Additionally, the check engine light will typically be illuminated when this code is present.

Comparing OBD-II and OBD-I Systems

The main difference between OBD-II and OBD-I systems is in their diagnostic capabilities. OBD-II systems are able to diagnose more complex issues than their predecessors, including those related to emissions control systems. In addition, OBD-II systems have standardized protocols for communication between the ECM and other components of the vehicle, whereas OBD-I systems used proprietary protocols.

Is Code P0118 Serious?

Yes, code P0118 can be serious if left unchecked. Any issue with your vehicle’s engine temperature sensor can cause serious damage if not addressed promptly. It’s important to take your car in for service if you’re experiencing any of the symptoms associated with this code.

Research Resources for Code P0118

If you’re looking for more information about code P0118, there are several online resources available to help you research this issue further. The websites of major auto parts manufacturers such as Autozone or Advance Auto Parts offer detailed information about this code and its associated symptoms and repairs. Additionally, many car forums offer valuable advice from experienced mechanics who can help answer any questions you may have about your car’s engine temperature sensor or other engine components.

FAQs About Code P0118

Here are some common questions about code P0118:

Q: What could cause this code?

A: Possible causes of this code include a faulty or damaged engine temperature sensor or a wiring issue in the system.

Q: How can I diagnose this issue?

A: You’ll need to use an advanced scan tool to diagnose this issue properly; it’s best to take your vehicle in to a qualified mechanic who has access to these tools if you’re not sure how to proceed on your own.

FAQ & Answers

Q: What is Code P0118?
A: Code P0118 is an OBD-II generic diagnostic trouble code indicating a problem with the Engine Coolant Temperature (ECT) circuit. It means that the ECT sensor signal is above or below the normal range of operating temperatures.

Q: What are the Possible Causes of Code P0118?
A: Possible causes of Code P0118 include a faulty ECT sensor, low or high coolant levels, an open circuit, a shorted circuit, and an excessive resistance in the ECT circuit.

Q: What Tools and Equipment are Needed to Diagnose Code P0118?
A: To diagnose Code P0118, you will need a digital multimeter, an OBD-II scanner, and a thermometer.

Q: Are There Common Fixes for Code P0118?
A: Common fixes for code P0118 include replacing the ECT sensor, checking the coolant level and ensuring that it is full if it is low, and repairing any open or shorted circuits in the ECT system.

Q: Is Code P0118 Serious?
A: Yes, code P0118 can be serious if left unresolved as it can cause engine performance issues such as poor fuel economy and reduced engine power. It can also lead to further complications such as damage to other components in the engine system if not addressed promptly.

In conclusion, Code P0118 means that the Engine Coolant Temperature (ECT) Sensor Circuit High Input. This code is typically an indication of a faulty ECT sensor or circuit, and should be inspected and repaired as soon as possible to prevent potential damage to the engine.

Author Profile

Carl Frisch
Carl Frisch
With more than 30 years in the bicycle industry, I have a strong background in bicycle retailing, sales, marketing and customer service. I have a passion for cycling and a dedication to excellence. As a manager, I worked diligently to increase my capabilities and responsibilities, managing up to eleven mechanics (at Palo Alto Bicycles) and later as a working partner in my own store.

As the shop owner of Spoke n’ Word Cycles in Socorro, NM, the success of the mission was my responsibility, which I pursued passionately since we opened in 2003 through the spring of 2011. I am adept at managing owned and loan inventory, preparing weekly & annual inventory statements, and managing staff. The role as managing partner also allowed me tremendous freedom. I used this personal freedom to become more deeply involved in my own advancement as a mechanic, to spearhead local trail building, and advocating for cycling both locally and regionally.

As a mechanic, I have several years doing neutral support, experience as a team mechanic, and experience supporting local rides, races, club events. I consistently strive to ensure that bicycles function flawlessly by foreseeing issues and working with the riders, soigners, coaches and other mechanics. Even with decades of experience as a shop mechanic and team mechanic, and continue to pursue greater involvement in this sport as a US Pro Mechanic, and UCI Pro Mechanic.

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