What Is the Check Engine Light, and What Does It Signify?

How to tell if your car has a loose fuel cap or a major engine issue

Here’s how the check engine light appears.

By Consumer Reports

As you're cruising down the road in your vehicle, a yellow warning light pops up on your dashboard indicating an issue with your engine. Like many drivers, you might be uncertain about what this signal means or how to respond appropriately.

Consider it the most perplexing signal on your instrument panel: The check engine light could indicate anything from an improperly secured fuel cap to a severely malfunctioning engine.

It doesn't imply that you must stop your vehicle on the roadside and summon a towing service," explains Dave Cappert from the National Institute for Automotive Service Excellence, an organization that assesses and credentials automotive technicians located in Virginia. "Instead, it suggests getting your car inspected at the earliest opportunity.

Disregard that warning, and you might damage costly parts. Additionally, this could indicate that your vehicle is experiencing reduced fuel efficiency and releasing greater amounts of emissions.

What Does the Check Engine Light Indicate?

The check engine light is an integral component of your vehicle’s onboard diagnostic system. Starting from the 1980s, computers began playing a larger role in controlling and monitoring vehicle performance, managing factors like engine speed, fuel mixture, and ignition timing. Additionally, contemporary vehicles use a computer to determine when the automatic transmission should change gears.

If a computer detects an issue within the electronic control system that it cannot fix, it activates a yellow warning indicator marked "check engine," "service engine soon," or "check powertrain." Alternatively, the light might simply display an image of an engine, possibly accompanied by the word "check."

Alongside activating the indicator known as the International Check Engine Light, the vehicle’s computer saves what is referred to as a "trouble code" within its system. This trouble code pinpoints the root cause of the issue, whether it involves a faulty sensor or a problematic engine operation. These codes can be retrieved using specialized tools like an electronic scanner or a diagnostic computer, which are commonly found in automotive service centers. Additionally, numerous budget-friendly code reader devices cater specifically to those who wish to diagnose issues themselves at home.

The code usually only guides you towards where the problem might be, and it still needs a skilled specialist to thoroughly identify and fix the issue. Given that getting a shop to perform a diagnostic check costs roughly $90, numerous vehicle owners are opting for online resources to determine both the source and solution of the problem. While this approach may succeed at times, one should always consult with an expert when unsure about how to proceed.

Photo: iStock

How to Address the Check Engine Light

When the check engine light comes on, it can flash or stay lit steadily, based on what’s wrong. If the light blinks, or appears as red rather than yellow or amber in certain vehicles, this signals an issue requiring urgent care. Regardless, get your car inspected by a professional technician soon.

In newer vehicles, a flashing indicator typically signifies a significant engine misfire causing raw fuel to be expelled through the exhaust system. This could swiftly harm the catalytic converter, resulting in costly repairs. Should this occur, it’s advisable to decrease your speed and get your vehicle inspected without delay.

Should the indicator remain constant, this signifies that the issue isn’t urgent; however, it would still be wise to book a service session at your earliest convenience. Modern car systems frequently attempt to adjust themselves when encountering faults, which means symptoms may go unnoticed. Nonetheless, these issues could lead to reduced gas efficiency and increased emission of harmful substances like hydrocarbons along with various contaminants from your vehicle.

The customer might ultimately end up costing themselves more money by keeping that light on and neglecting it," said Jim Collins, who leads the national training team at Ford Motor Co., during an interview with CR. In certain severe instances, the vehicle's computer could decrease power output in order to minimize the chance of harm.

Occasionally, when the check engine light comes on, your vehicle might enter a “limp home” mode. In such cases, you'll find that your car lacks power and certain features could shut down; however, steering and braking functions should remain operational. This allows you to potentially drive back home or reach an auto dealership or repair shop. Should these options not be feasible due to distance, it would be wise to exit the roadway and summon roadside assistance for towing.

Should the check engine light illuminate, consider these steps for how to proceed:

Find a critical issue that demands urgent consideration. Examine your instrument panel gauges and warning lights for signs of low oil pressure or overheating. If these issues appear, you should safely pull over and turn off the engine at the earliest opportunity. In certain vehicles, a yellow check engine light suggests investigating the issue, whereas a red one indicates an urgent need to stop immediately.

Attempt to secure your gas cap more tightly. This usually resolves the issue. Just be aware that it might require multiple attempts for the light to reset. Certain cars feature an additional warning signal indicating when the fuel cap isn’t secured properly.

Reduce speed and load. Should the check engine light flash or if you experience significant performance issues like reduced power, decrease your velocity and lessen stress on the engine. An advisable step might include ceasing to pull a trailer. It’s best to get your vehicle inspected at the earliest opportunity to avoid costly repairs.

Use built-in diagnostic services, If available, numerous contemporary vehicles come equipped with built-in remote diagnostic features, enabling them to communicate error codes and set up maintenance appointments. Currently, several car manufacturers such as Stellantis, Ford, Hyundai, Jaguar/Land Rover, and Volvo offer these remote diagnostic services along with the option to arrange for vehicle servicing directly from your device.

Decoding Dashboard Warning Lights

When you turn on your vehicle, you may have observed the series of icons displayed on your dashboard. During an episode of the television program "Consumer 101," Consumer Reports' specialist Jen Stockburger elucidated these warning symbols and their meanings to host Jack Rico.

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