GMC Sierra (2014-2019) check engine light diagrams & schemes

Years of production: 2014 2015 2016 2017 2018 2019


The GMC Sierra is a popular truck known for its durability and reliability. However, like any other vehicle, it may experience some issues over time. One of the most common problems that drivers face is the check engine light coming on. This warning light can indicate a variety of issues with your truck's engine or emissions system.

There are several reasons why your GMC Sierra's check engine light may come on. Some of the most common causes include faulty oxygen sensors, malfunctioning catalytic converters, loose gas caps, and damaged spark plugs or wires. In some cases, more serious issues such as failed mass airflow sensors or damaged exhaust systems might also trigger this warning light.

Fortunately, fixing the problem behind a check engine light isn't always complicated or expensive. The first step in addressing this issue is to have your truck's diagnostic code read using an OBD-II scanner tool. This will help you determine what specific problem triggered the warning light so that you can take appropriate action.

Depending on the cause of your vehicle's check engine light coming on, there are different steps you can take to fix it. For example, if a loose gas cap caused the issue then simply tightening it up should solve the problem quickly and easily. If more significant repairs are needed such as replacing an oxygen sensor or catalytic converter then professional assistance from a mechanic might be necessary.

Overall understanding why your GMC Sierra's check engine light came on and how to fix it doesn't have to be too difficult with proper knowledge and guidance available online today.

Understanding Check Engine Light

The check engine light is a warning signal that illuminates on your car's dashboard. It indicates that there's an issue with one of the vehicle systems or components, which can affect its performance, safety, and emissions. The check engine light (CEL) is also known as the malfunction indicator lamp (MIL) or service engine soon (SES) light.

The CEL operates by detecting a fault in the onboard diagnostic system (OBD), which monitors various sensors and systems in your car. When it detects a problem, it triggers the CEL to illuminate and store a trouble code in the OBD memory. The code corresponds to a specific problem area, such as emissions control, fuel delivery, ignition system, transmission system, etc.

If you ignore the CEL for too long or fail to diagnose and fix the underlying problem promptly, you could end up damaging other parts of your car or experiencing costly repairs later on. Therefore it's crucial to understand what causes GMC Sierra check engine light issues and how to fix them correctly.

Common Causes of Check Engine Light Issues

GMC Sierra owners may experience different reasons behind their check engine lights coming on; some of these include:

  • Faulty oxygen sensor: This component measures how much oxygen is present in exhaust gases leaving the catalytic converter. If faulty, it can cause high fuel consumption levels & increase harmful emissions.
  • Fuel cap issues: A loose gas cap can trigger false alarms by allowing fumes out into ambient air rather than through emission control devices like EVAP systems;
  • Malfunctioning Mass Air Flow Sensor: Malfunctioning MAF Sensors do not regulate airflow properly- leading to stalling engines;
  • Bad Spark Plugs: Worn-out spark plugs can cause misfires and poor engine performance, lowering fuel efficiency levels.;
  • Dead battery or alternator problems: A dead battery can trigger a check engine light, as well as issues with the alternator.

How to Fix Check Engine Light Issues on Your GMC Sierra

The first step in fixing your GMC Sierra check engine light is to diagnose the underlying problem accurately. This requires using an OBD scanner, which reads the trouble code stored in your car's computer system and displays it on a screen or printout.

Once you've identified the issue, you'll need to fix it by replacing or repairing any damaged parts. Some common solutions for check engine light issues include:

  • Fuel Cap Replacement: Simply replacing your gas cap could be all it takes to fix this common issue;
  • Oxygen Sensor Replacement: Replacing faulty oxygen sensors can help reduce emissions and improve fuel efficiency levels;
  • Maf Sensor Cleaning/Replacement- Regular cleaning helps prevent damages that lead to malfunctioning MAF Sensors;
  • New Spark Plugs & Ignition Coils Replacements- Installing new spark plugs & ignition coils improves combustion & power output while saving fuel consumption levels.;
  • Battery/Alternator Repair or Replacement- If these are faulty, they should be repaired/replaced promptly by qualified mechanics who will also reset CEL codes properly after repair services.

In conclusion, understanding check engine lights' causes and how to fix them properly is essential for maintaining optimal vehicle performance and safety while avoiding costly repairs later on. Visit our service center at XYZ Motors if you experience any GMC Sierra check engine light issues today!

Causes of Check Engine Light in GMC Sierra

The check engine light is an important warning indicator that alerts drivers to potential problems with their vehicle. When this light comes on in your GMC Sierra, it can be concerning and confusing. Here are some common causes of the check engine light in a GMC Sierra:

  • Faulty oxygen sensor: When the oxygen sensor fails in your GMC Sierra, it can cause a decrease in fuel efficiency and increase emissions. This may trigger the check engine light to come on.
  • Loose or damaged gas cap: A loose or damaged gas cap can cause fuel vapors to escape from the tank which leads to a drop-in fuel efficiency and higher emissions, resulting in triggering the check engine light.
  • Catalytic converter failure: If you notice a reduction in power when driving your GMC Sierra along with rough idle or unusual exhaust smell, then there might be an issue with catalytic converter due to which Check Engine Light get triggered.
  • Mass airflow sensor failure: The mass airflow (MAF) sensor helps regulate air intake for optimal performance. If this component fails, it results into poor acceleration & reduced gas mileage so as triggers off the Check Engine Light too
  • Faulty ignition coil packs: If one or more ignition coil packs fail, they will send faulty signals to other components leading up-to missfires thereby triggering off Check Engine Light.

In some cases where multiple issues are detected by onboard diagnostics system simultaneously might result into illuminating various warning lights besides just the "Check Engine" such as ABS light/ Traction Control System / Oil Pressure etc depending upon the nature of detected fault. Make sure to get all issues checked and fixed for safe & reliable driving experience.

How to Diagnose Check Engine Light in GMC Sierra

The check engine light is an important warning system that alerts you of any issues with your vehicle. It can be a cause for concern when it appears on the dashboard of your GMC Sierra, but it's also helpful because it indicates there's something wrong that needs to be addressed. Here are some steps you can follow to diagnose the check engine light in your GMC Sierra.

Step 1: Check Your Gas Cap

The first step in diagnosing the check engine light is to make sure that your gas cap is properly secured. A loose or faulty gas cap can trigger the check engine light and cause other problems with fuel efficiency and emissions. If you notice that the cap is loose or damaged, replace it immediately and see if the check engine light turns off.

Step 2: Use an OBD-II Scanner

If securing your gas cap doesn't fix the issue, then using an OBD-II scanner may help diagnose what's causing the problem. This scanner connects to your vehicle's computer system and reads error codes stored within it. These codes will help identify which system has malfunctioned and gives you a starting point for troubleshooting.

Step 3: Troubleshoot Based on Error Codes

Once you have identified which error code(s) triggered the check engine light, begin troubleshooting based on those codes' descriptions:

  • If there are misfire codes (P0300-P0315), this could indicate issues with spark plugs or ignition coils.
  • If there are oxygen sensor codes (P0130-P0167), this could mean problems with oxygen sensors or catalytic converters.
  • If there are EVAP System Codes (P0440-P0456), this could indicate a problem with the fuel tank, purge valve, or charcoal canister.
  • If there are transmission codes (P0700-P0999), this could mean problems with the transmission control module or solenoids.

Step 4: Seek Professional Help

If you're unsure about how to proceed based on the error codes, it's best to seek professional help from a mechanic or dealership. They'll have experience working on GMC Sierras and will be able to diagnose and fix problems more efficiently than if you were doing it yourself. It's important not to ignore your check engine light as it could lead to further damage that is costly in the long run.

By following these steps and being diligent about resolving any issues that arise, you can keep your GMC Sierra running smoothly for years to come.

Common Check Engine Light Codes in GMC Sierra

If your GMC Sierra has its check engine light on, there are a few common codes that may be causing it:

  • P0101: Mass Air Flow Circuit Range/Performance issue.
  • P0300: Random/Multiple Cylinder Misfire Detected.
  • P0420: Catalyst System Efficiency Below Threshold Bank 1.
  • P0446: Evaporative Emission Control System Vent Control Circuit Malfunction.
  • P0455: Evaporative Emission Control System Leak Detected (Gross Leak).

The P0101 code indicates an issue with the mass air flow sensor. This sensor measures the amount of air entering the engine and tells the computer how much fuel to inject into each cylinder. If this sensor is not working properly, it can cause poor performance and reduced fuel economy.

The P0300 code indicates that there is a random or multiple cylinder misfire detected. This could be caused by several things including bad spark plugs, ignition coils, or fuel injectors. It is important to get this issue fixed as soon as possible to prevent damage to your engine’s catalytic converter.

The P0420 code indicates an issue with the catalytic converter system on bank one of your vehicle’s exhaust system. The catalytic converter reduces harmful emissions from your car’s exhaust before they are released into the atmosphere. If this system is not functioning properly, you may fail emissions testing and potentially harm the environment.

The P0446 code indicates an issue with the evaporative emission control system vent control circuit malfunctioning. This could lead to increased emissions and decreased fuel efficiency. It is important to get this issue fixed as soon as possible.

The P0455 code indicates an issue with the evaporative emission control system leaking a significant amount of fuel vapor into the atmosphere. This could lead to increased emissions and decreased fuel efficiency. It is important to get this issue fixed as soon as possible.

To see all possible error codes click here:

How to Fix Check Engine Light in GMC Sierra

If your check engine light comes on in your GMC Sierra, it is important that you address the issue as soon as possible. Not only can a lit check engine light be annoying, but it can also indicate a more serious problem with your vehicle's performance. Here are some steps you can take to fix the check engine light in your GMC Sierra:

Step 1: Check for Loose Gas Cap

The first thing you should do when your check engine light comes on is to make sure that your gas cap is tightly secured. A loose or damaged gas cap can cause fuel vapors to leak out of the tank, which triggers the check engine light.

Step 2: Use an OBD-II Scanner

An OBD-II scanner is a diagnostic tool that plugs into your vehicle's computer system and provides information about any error codes that have been triggered. You can purchase an OBD-II scanner from most auto parts stores or online retailers. Once you have plugged the scanner into the port under the dashboard, follow its instructions to read and clear any error codes.

Step 3: Replace Faulty Parts

If the OBD-II scanner identifies a faulty part as being responsible for triggering the check engine light, it will provide you with specific information about what needs to be replaced or repaired. Depending on what part needs replacing, this may be something you can do yourself if you are comfortable working on cars. Alternatively, you may need to take your GMC Sierra into an authorized dealer or mechanic for repairs.

Step 4: Reset Your Vehicle's Computer System

To ensure that any changes made during repairs have been correctly registered by your vehicle's computer system and won't continue causing the check engine light to come on, you should reset the system. You can do this by disconnecting the negative battery cable for a few minutes and then reconnecting it.

By following these steps, you can fix the check engine light in your GMC Sierra and ensure that your vehicle is running smoothly once again.

Prevention Tips for Check Engine Light in GMC Sierra

To prevent the check engine light from coming on in your GMC Sierra, there are several steps you can take. Here are some tips:

1. Regular Maintenance:

Regular maintenance is essential to keep your vehicle running smoothly and avoid unexpected problems like a check engine light. Make sure to follow the manufacturer's recommended maintenance schedule, including oil changes, air filter replacements, and tune-ups.

2. Keep an Eye on Fluid Levels:

Low fluid levels can cause problems with your vehicle's performance and trigger the check engine light. Check your oil level regularly and make sure other fluids like coolant, brake fluid, power steering fluid, and transmission fluid are at proper levels.

3. Drive Carefully:

Reckless driving or rough handling of your vehicle can cause damage to vital components that may result in a check engine light illuminated on the dashboard. Be cautious when driving over potholes or uneven roads.

4. Use Quality Fuel:

Using low-quality fuel or contaminated fuel may lead to issues with fuel system components such as spark plugs causing misfires which result in a check engine light being turned on; Ensure you use high-quality gasoline specified by the manufacturer only.

5. Don't Ignore Warning Signs:

If you notice any unusual sounds or behavior from your vehicle while driving (for example: vibrations), have it checked immediately instead of waiting until later since this could end up damaging more parts resulting in expensive repairs later down-the-line. By following these prevention tips , you'll be able to reduce the likelihood of experiencing a check-engine-light-illuminated-dashboard warning sign while also potentially saving yourself money by avoiding costly repairs due to neglecting routine services such as oil changes!


In conclusion, the check engine light in your GMC Sierra can be caused by various factors. Some of these factors include a faulty oxygen sensor, loose gas cap, damaged catalytic converter, and low fuel pressure. It is important to take immediate action when you notice the check engine light on to avoid further damage to your truck's engine.

The first step towards fixing the problem is reading the diagnostic trouble codes using an OBD-II scanner or taking your vehicle to a mechanic for diagnosis. Once you have identified the root cause of the issue, it is essential to fix it as soon as possible.

Some causes like replacing a damaged gas cap are easy fixes that you can do at home without professional help. However, other issues like repairing a faulty catalytic converter may require more technical know-how and expertise from a certified mechanic.

To prevent future occurrences of check engine lights in your GMC Sierra or any other car model, ensure that you perform regular maintenance checks such as oil changes and tune-ups regularly. Additionally, address any warning signs before they escalate into larger problems that may lead to costly repairs.

In summary; always pay attention to warning signs from your truck's dashboard and maintain regular servicing schedules for optimal performance for both short-term reliability & longevity in life span!

All GMC Sierra info & diagrams provided on this site are provided for general information purpose only. Actual GMC Sierra (2014-2019) diagrams & schemes (fuse box diagrams & layouts, location diagrams, wiring diagrams etc.) may vary depend on the model version.
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