Blog Car Care Advice Top 8 Causes Behind a GMC Check Engine Light (+ How to Fix)
Car Care Advice

Top 8 Causes Behind a GMC Check Engine Light (+ How to Fix)

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The dreaded GMC check engine light illuminating your dashboard is enough to have anyone wondering: What’s wrong with my car? 

While the little yellow light is undoubtedly a concern, it may just be a loose gas cap that needs tightening. However, if you notice other symptoms, something more serious may be wrong.

Let’s dive into the most common causes of a GMC check engine light, what to do when it activates, and more.

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Let’s get started.

What Causes GMC Check Engine Light to Turn On?

Regardless of which GMC vehicle you’re driving, your check engine warning light will activate when the car’s computer detects a fault and generates a diagnostic trouble code. 

Let’s look at some of the most common causes of an activated check engine light:

1. Loose Gas Cap

A simple loose gas cap could be the reason for your check engine light activating. A loose or damaged gas cap can affect fuel pressure and cause fuel vapors to escape. This can reduce your fuel economy while increasing your emissions.

2. Faulty Oxygen Sensor (O2 Sensor)

A car’s oxygen sensor (O2 sensor) monitors the oxygen level in exhaust gases. With time, a build-up of contaminants can eventually lead to issues with the oxygen sensor, triggering the check engine light. A faulty oxygen sensor can cause rough idling, poor engine performance, and impaired fuel economy. 

3. Bad Spark Plug or Spark Plug Wires 

Spark plugs ignite the air-fuel mixture in the combustion chamber. Failing spark plugs or spark plug wires can cause a misfiring engine, poor acceleration, and increased exhaust smoke, which may trigger the check engine light. 

4. Defective Mass Airflow Sensor

The mass airflow sensor (MAF) measures the air entering the engine, ensuring the correct amount of fuel gets mixed with the air. Aside from activating the check engine light, a faulty MAF can lead to emission issues, poor engine performance, and stalling

5. Vacuum Leak

GMC vehicles have a vacuum system that routes gasoline fumes through the engine to lower emissions. A vacuum leak can result in the engine light activating, higher or fluctuating RPMs when idling, and reduced fuel efficiency.

6. Defective Catalytic Converter

The catalytic converter helps reduce your vehicle’s emissions by converting harmful gases into less harmful ones. A faulty catalytic converter can dramatically impact fuel efficiency and vehicle performance, triggering the engine light. 

7. Old or Low Battery

Whether driving the 2023 GMC Sierra or any other GMC vehicle, your car won’t start without a battery. A failing battery may inadvertently trigger a check engine light if it provides insufficient voltage to the car’s computer. 

8. Low Oil Pressure 

If it’s been a while since you’ve had an oil change, low oil pressure could cause an illuminated check engine light. An additional oil light may also be activated on your dashboard, suggesting it’s time for an oil change.

Next, let’s see what to do when the check engine light activates.

What to Do if Your GMC Check Engine Light Turns On?

Generally, your check engine light will activate and remain illuminated, but that may not always be the case. Let’s see what you should do on a case-by-case basis:

A. Illuminates Under Certain Conditions

If the check engine light only activates under certain conditions, it suggests the problem is intermittent or that a part is on the verge of failing. If you notice any performance or gas mileage issues while the light is activated, your best bet is to book a GMC service with a trusted mechanic

B. Is Constantly On

A constantly illuminated check engine light suggests something has gone wrong and requires fixing. There are many potential causes, ranging from a loose gas cap to a misfiring engine. Your vehicle may sound all right, but it’s best to book a service as soon as possible. Ignoring the check engine warning light could lead to costly repairs down the line. 

A flashing check engine light while driving suggests a serious issue. You should stop driving and pull over as soon as it’s safe to do so. Continuing driving could risk significant damage to vital engine components, such as the spark plug set or the ignition coil, resulting in a more expensive repair job. The best thing to do here is to have your car towed or consult a mobile mechanic for a check engine light diagnosis.

Now that we’ve covered what to do, let’s see how to reset the check engine light. 

How to Reset the Check Engine Light

Your check engine light should automatically turn off after fixing the problem. You can also use an OBD-II scanner to reset the code. However, if the issue persists, the light will reactivate.  

Alternatively, you can manually reset the light by disconnecting the battery. Here’s a brief walkthrough: 

  1. Ensure your truck is off and positioned securely with the parking brake on.
  2. Find the negative terminal on your car battery, indicated with a black cap and the negative symbol (-).
  3. Loosen the negative nut or bolt on the negative terminal.
  4. Wait 30 to 60 seconds, then reconnect the negative terminal.
  5. Turn on your vehicle’s ignition to check if the engine light and the trouble code are reset.

Wondering how much a check engine light diagnosis costs?
Read on to find out.  

How Much Does it Cost to Get a GMC Check Engine Light Diagnosed?

The average cost of a check engine light diagnosis is around $88 – $144. However, the actual cost of the repairs will vary depending on the trouble code and the damaged part. You should always book a GMC service with a qualified mechanic for the most cost-effective vehicle repairs.

Wrapping Up

Whether you’re driving a GMC Sierra or some other GMC truck, there are many potential causes for a GMC check engine light. In some cases, the little yellow light should be an easy fix. However, its severity can vary depending on whether you have an intermittent, constant, or flashing check engine light. It’s best to address it as soon as possible and, ideally, avoid driving to reduce the risk of a more expensive repair job. 

So why not have AutoNation Mobile Service take care of the diagnosis right from your driveway? 
Our expert mechanic will tackle the GMC check engine light using new inventory for the required repair. You also get a 12-month | 12,000-mile warranty on all services. 

Fill out this form for an accurate engine light diagnosis estimate.