2020 GMC Sierra 1500 Has A Check Engine Light

Resolve Check Engine Light Issues in 2020 GMC Sierra 1500

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Reviewed by
Bo Fader
Written by RepairPal Car Genius
Updated January 14, 2025
0%
40% chance it's the
Emissions System
0%
60% chance it's
Something else
The most common reasons a 2020 GMC Sierra 1500 has a check engine light are an emissions system component, a sensor, or a catalytic converter.
  • Emissions System: A faulty emissions system component, such as an oxygen sensor or EGR valve, can lead to increased emissions and trigger the check engine light.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a 2020 GMC Sierra 1500 has a check engine light?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

A faulty oxygen sensor is one of the most common causes of a check engine light. Symptoms may include a decrease in fuel mileage, hesitation or misfiring from the engine, rough idling or even stalling. A faulty sensor may cause the vehicle to fail an emissions test.

Any time there is an emissions fault the check engine light will be displayed. The purpose of the check engine light is to inform the driver that an emission related fault has been found, and that there are on-board diagnostic (OBD) trouble codes stored in the powertrain or engine control module. Additionally, since the emissions systems are so intertwined into engine control and transmission control systems, symptoms may include nearly any sort of drivability concerns. This may include harsh shifting, failure to shift, hesitation on acceleration, jerking, engine failure to start or run, loss of power, or any number of other drivability issues.

Due to the nature of electrical systems on modern vehicles, the range of problems these can cause are nearly limitless. However, there is a way to categorize them in two ways. Permanent and intermittent problems. Permanent problems appear and remain. This may be the vehicle will not start, the radio does not work, or the door chime will not turn off among many, many others. These problems are more straight-forward to diagnose since they present themselves at all time. This means there will always be a fault to find. Intermittent electrical problems, however, can be difficult or impossible to locate, since they appear then disappear without warning. The best case scenario for an intermittent issue is when replicating the problem is easily accomplished and understood. This allows a technician to make an issue semi-permanent, allowing them to find the fault. Other issues that come and go without warning and cannot be replicated on demand must occur when the technician is servicing the vehicle, otherwise there is no problem to correct. It is most important to understand that electrical system faults always require inspection, and can include the vehicle working in any manner, or not working at all.

Like we noted in the last section, general diagnosis symptoms are the most vague of the bunch. There are several diagnostic spectrums, electrical diagnosis, drivability diagnostics, engine diagnostics, transmission diagnostics, and the list could continue for about 5 or 10 more spectrums of diagnostics. The most important take-away here, is that general diagnostics are diagnostics that have no other spectrum in which they fit, or the problem is unknown. This means that any vehicle left outside of a repair facility with the keys and an authorization to perform diagnosis will be diagnosed under the general diagnosis spectrum.

When the Check Engine Light comes on, you may experience engine performance issues such as poor acceleration, rough idling, or an engine that won't start. In some cases, no abnormal symptoms will be experienced. Other systems like the transmission or ABS can cause the Check Engine Light to illuminate and lights for those systems can come on at the same time. Similar lights may say "Check Engine Soon", "Malfunction Indicator Light" or just "Check". In rare case the engine can overheat.

What are the initial diagnostic steps to take for a check engine light on a 2020 GMC Sierra 1500?

When faced with a check engine light on your 2020 GMC Sierra 1500, it's essential to adopt a systematic diagnostic approach. Start by checking the gas cap; a loose or damaged cap is a common culprit that can easily trigger the light. Next, take a moment to inspect your dashboard gauges for any additional warning lights or irregular readings that might indicate other underlying issues. Utilizing an OBD-II scanner is a crucial step, as it allows you to retrieve specific error codes that can guide you toward the exact problem. Additionally, inspect the spark plugs for any signs of wear or damage, as faulty plugs can lead to engine performance issues. Finally, ensure that all essential fluid levels—such as oil, coolant, and transmission fluid—are adequate, as low levels can also activate the check engine light. By following these initial steps, you can effectively narrow down the potential causes of the warning light and take informed action to resolve the issue.

What are the common problems that could cause the check engine light to illuminate in a 2020 GMC Sierra 1500?

When the check engine light comes on in a 2020 GMC Sierra 1500, it can be a source of concern for any DIY mechanic. One of the most straightforward issues to check is the gas cap; a loose or damaged cap can easily trigger the light, so ensuring it is secure is a good first step. If the gas cap is fine, the next likely culprit could be the oxygen sensor, which plays a crucial role in fuel efficiency and emissions control. A malfunctioning sensor can lead to poor performance and should be inspected. Additionally, problems with the catalytic converter can also cause the check engine light to illuminate, often indicating a more serious issue that may require professional attention. Other components to consider include the mass airflow sensor, which affects the air-fuel mixture, and spark plugs, which, if worn or faulty, can lead to engine misfires. Ignition coil issues can similarly impact engine performance, while the exhaust gas recirculation (EGR) valve may also be a source of trouble if it becomes clogged or malfunctions. Addressing these common problems promptly is essential to maintain the vehicle's performance and prevent further damage, making it advisable to consult a qualified mechanic for a thorough diagnosis if the light persists.

How urgent is it to address the check engine light in a 2020 GMC Sierra 1500?

When the check engine light illuminates in your 2020 GMC Sierra 1500, it is essential to recognize the urgency of the situation. This warning light is not merely a nuisance; it indicates that your vehicle's onboard diagnostics have detected a potential issue that could range from a minor sensor malfunction to a serious engine problem. Ignoring this warning can lead to decreased fuel efficiency, increased emissions, and even severe engine damage, which can be costly to repair. For DIY enthusiasts, the first step should be to use an OBD-II scanner to retrieve diagnostic trouble codes, which can provide insight into the specific issue at hand. However, it is crucial to act quickly, as some problems can escalate into safety hazards or lead to more extensive repairs if left unaddressed. By taking prompt action, you not only safeguard your vehicle's performance but also ensure your safety on the road.

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