Should You Keep Driving When Your Check Engine Light Comes On?
TLDR
- A solid check engine light means you can usually continue driving briefly but you should book a diagnostic scan within a day or two
- A flashing check engine light signals an active engine misfire and you should reduce speed and get to a shop as soon as possible
- Continuing to drive with a flashing light risks serious damage to your catalytic converter and significantly higher repair costs
The check engine light tends to come on at the worst possible times: the night before a long drive, during rush hour, or when you are already running behind. The first question almost every Thornhill driver asks is whether it is safe to keep going. The answer depends on how the light is behaving and whether anything else feels different about your vehicle. A 2025 study found that only
36% of drivers get their check engine light inspected within the first week of it turning on (https://www.reviews.com/insurance/car/only-36-of-drivers-get-the-check-engine-light-inspected/), meaning the majority of drivers delay a diagnosis that could reveal a manageable problem before it grows.
Solid vs. Flashing Check Engine Light
A Solid Check Engine Light
A steady, solid check engine light means your vehicle's onboard diagnostic system has logged a fault code. The issue is real and needs to be addressed, but it is typically not an emergency. Most solid check engine lights are related to sensors, emissions components, or minor system faults that do not immediately affect your ability to drive safely.
In our shop, we regularly see vehicles that arrive with a solid check engine light that has been on for three months or longer. The issue that triggered it has often compounded during that time. What could have been a straightforward repair has grown into a more expensive one simply because the driver did not have the fault read early enough. We recommend booking a diagnostic scan within a day or two of the light coming on.
As automotive industry experts note,
a fault code by itself is not a diagnosis but rather a starting point for further testing. Without knowing what the code is, there is no safe way to assume the issue is harmless.
A Flashing or Blinking Check Engine Light
A flashing check engine light is a different situation entirely. This is your vehicle signaling an active engine misfire severe enough to cause damage right now. When an engine misfires, unburned fuel passes through the exhaust and into the catalytic converter. The converter can overheat rapidly, and sustained exposure will permanently damage it.
If your check engine light is blinking, reduce your speed and avoid hard acceleration. If possible, avoid highway driving. Get your vehicle to a shop as soon as you safely can. Do not assume a flashing light will resolve on its own.
Other Warning Signs That Raise the Urgency
While the behavior of the check engine light itself is the most reliable indicator of urgency, there are additional symptoms that suggest a more serious situation regardless of whether the light is solid or flashing.
If you notice any of the following alongside the check engine light, treat it as a higher-priority situation:
Rough idling or a noticeable vibration at a stop- A strong smell of fuel or rotten eggs from the exhaust
- Significant loss of power when accelerating
- Steam or smoke from under the hood
- A noticeable drop in fuel economy over several days of driving
Any of these symptoms combined with a check engine light should prompt a same-day visit rather than waiting.
What To Do If the Light Comes On During a Long Drive
If you are already on the road when the light comes on, the steps are straightforward. Note whether the light is solid or flashing. Pay attention to how the vehicle is performing. If the light is solid and the car is running normally, you can continue to your destination but should have it looked at promptly. If the light is flashing or if performance has changed noticeably, find a safe place to pull over and call for assistance.
FAQs
How long can I drive with a solid check engine light before it becomes a problem?
There is no universal answer because it depends on what triggered the light. Some faults are stable for a long time while others can worsen quickly. As a general guideline, we recommend booking a diagnostic within one to three days of the light coming on rather than waiting weeks. The sooner you know what triggered it, the better position you are in to manage the repair.
What happens if I keep ignoring the check engine light?
Ignoring it runs two risks. First, whatever triggered the light may get worse, turning a lower-cost repair into a higher-cost one. Second, in Ontario, your vehicle cannot pass the Drive Clean emissions test while the check engine light is on, meaning an ignored fault can become a compliance issue at test time. Neither is a good outcome when a same-week diagnostic could have resolved the issue early.
Can I get my car through an Ontario emissions test with the check engine light on?
No. In Ontario, a vehicle with an active check engine light will not pass the Drive Clean emissions test. The light must be off and the related codes must have completed their readiness monitors before the vehicle can pass. You will need to have the fault diagnosed and repaired before booking the test.
Come See Us in Thornhill
If your check engine light is on, our team at MR Automotive is ready to help you figure out what it means and what to do next. Our technicians are certified through Skilled Trades Ontario. Book a check engine light diagnostic or call us at (905) 882-2277. We are open Monday through Friday, 8:00 AM to 5:00 PM. After-hours drop-off is available 24/7 for your convenience.
Our Location
MR Automotive
Address:
83 Glen Cameron Rd, Thornhill, ON L3T 1N8
Phone Number:
(905) 882-2277
Hours: Monday to Friday, 8:00 AM to 5:00 PM
