GMC Check Engine Light Stays On

Is the Check Engine Light illuminating on your GMC dashboard? Learn what is causing the check engine light to illuminate and the possible solutions to remove the warning light from your GMC.

Whenever a GMC vehicle detects a powertrain or EVAP-related problem, it will inform the driver by turning on the check engine light on the dashboard. GMC check engine light can be quite frustrating, as the yellow warning light doesn’t provide much information about the problem.

gmc check engine light cel service engine soon

This article looks at common problems that trigger the check engine light in GMC vehicles and how to read the fault codes yourself with an OBD-II scanner.


Depending on the cause of the check engine light on your GMC, you may notice any of the following problems:

  • Engine power is reduced.
  • GMC runs rough
  • The vehicle won’t idle; it keeps dying.
  • Engine misfire present
  • Lack of power
  • Poor throttle response
  • Smoke from the exhaust
  • The transmission won’t shift gears.
  • The vehicle goes in limp home mode/emergency mode.
  • Check engine light stays on or flashes.

You may not notice performance issues in some cases, such as an EVAP leak or a loose gas cap. Don’t ignore the GMC check engine light because even if there are no symptoms, fuel consumption may be higher when the check engine light stays on.

How to Diagnose and Reset GMC Check Engine Light?

The check engine light does not provide much information. To find out why your GMC check engine light is on, read the fault codes with an OBD-II scanner.

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If you want a more professional OBD-II scanner that can read and clear fault codes through every control module of your vehicle, use the YOUCANIC Full System Scanner.

  1. Locate the OBD-II port under the dashboard. Plug the scanner into the OBD-II port.gmc obd2 port location
  2. Turn on the ignition but do not start the engine.
  3. Allow the OBD-II scanner to turn on and enter to connect with the vehicle.
    PXL 20220312 003004456
  4. Select Read Codes or Read Faults, depending on the scanner.

Write down all the fault codes and research them to understand better the possible cause of the check engine light on your GMC.

Fix all the current problems, then go back to the main menu and select Clear Fault Codes.

Common problems cause the GMC check engine light to come on.

gmc maf sensor

Check engine light can be triggered by many problems. Some of the most common causes include:

  • Faulty MAF sensor
  • Bad oxygen sensor
  • Loose or defective gas cap
  • Clogged catalytic converter
  • Worn spark plugs
  • Defective ignition coil
check engine light on
  • Vacuum Leaks:  Misfires are quite a common problem on GMC trucks. Tracing down the source of the problem can be tricky, as it usually happens sporadically.  In addition to checking spark plugs and ignition coil, you should also inspect the intake for eventual vacuum leaks. Code: P0300
  • EGR Valve: A carbon buildup is a common cause of various EGR-related problems. While this will not affect engine performance generally, it might cause higher fuel consumption. Carbon buildup can be cleaned with EGR cleaner spray if not too extreme. Related Fault Code: P0401
  • Catalytic Converter: Higher mileage GMC trucks will likely experience emission control issues. In most cases, this is caused by a worn-out catalytic converter, especially if the truck suffered from a prolonged misfire. Another possibility is a faulty downstream O2 sensor. Related Fault Codes: P0420 and P0430
  • EVAP leak: The EVAP system is a frequent failure point. In addition to faulty vents or purge valves, these problems can be caused by various EVAP leaks. Finding a leak, usually due to cracks in EVAP lines, is best done with a smoke-generating machine. Related Fault Codes: P0442, P0445, and P0449.
  • Variable Timing Issues: Most newer VORTEC engines have variable valve timing for better performance. This system depends on good oil pressure within VVT solenoids.  If oil changes are neglected, screens on these solenoids get clogged with oil sludge and other contaminants. This obstructs oil flow and throws off the timing, resulting in a lack of acceleration and hesitation. In most cases, solenoids and screens can be cleaned. Related Fault Code P1345 (crankshaft/camshaft correlation)


Hundreds of possible problems can cause the check engine light on a GM vehicle to come on. The most common issues are spark plugs, oxygen sensors, and catalytic converter failure. Instead of guessing what is wrong, use an OBD-II scanner to read the fault codes.

Why is my GMC Check Engine Light Flashing On and Off?

One thing that must never be ignored is the check engine light flashing, especially if accompanied by engine shaking and juddering. A check engine light going on and off intermittently signals an engine misfire, causing damage to the catalytic converter and other engine components. It is not recommended to drive if the check engine light is flashing.

What to do when the GMC check engine light comes on?

gmc check engine light on

With a “check engine” light on, you need to find out what caused it. You can take your car to the workshop for a full diagnosis or get your OBD-II scanner. Your local auto parts store may also read the codes free of charge.

OBD-II scanners come in all shapes, sizes, and prices. The choices range from something simple as a Bluetooth OBD adapter that connects to an application on your smartphone over dedicated hand-held scan tools, to powerful diagnostic tools.

We hope you find the GMC Check Engine Light Stays On guide helpful. Check these troubleshooting and repair guides for more help on your GMC.


  • Rushit Hila • ASE Certified

    Rushit Hila, an ASE-certified engineer (G1 Automotive Maintenance and Repair), brings over two decades of hands-on experience in the automotive world to his writing. With a strong educational background, including a Master of Science in Engineering and a Bachelor of Science in Engineering, he has honed his skills and expertise through years of practical work. As a respected authority in the field, Mr. Hila is dedicated to offering insightful and valuable content that resonates with both vehicle owners and mechanics.

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