Driver Takes Toyota Tundra To Mechanic Because Of Check Engine Light. Then The Mechanic Realizes He Shouldn’t Have: ‘Free Money’

A mechanic says a 2025 Toyota Tundra with a flashing Check Engine light is the perfect example of why technicians shouldn’t skip the basics.

User @mdttoyotech, who says he’s an L1 ASE-certified master diagnostic automotive technician, shared how a simple visual inspection helped him quickly figure out what was wrong.

“This is why it’s important to always do visual inspections before you waste your time,” he says.

@mdttoyotech says he was diagnosing a 2025 Toyota Tundra that had just about 7,000 miles on it when it came in with a flashing check engine light. After pulling the truck into his shop’s bay, he shared a reminder for other technicians.

“When you’re a flat-rate technician, you want to save as much time as possible,” @mdttoyotech explains.

He then shows himself connecting the truck to the shop’s computer to scan for the issue but says he’ll also do a visual inspection. That’s when he checks the gas cap and discovers the problem. In the comments section, he explained that it was “left loose or off.”

“If the gas cap is left loose or off, it will set a thing called an emissions EVAP leak, where fuel emissions are somehow leaking out of the system from an unsealed part of the fuel system, mainly an emissions thing for the government in the environment,” he explained.

In other words, checking the truck himself before relying only on the scan saved him time and pointed him toward a much simpler fix. As of this writing, the video has more than 25,800 views.

Can A Gas Cap Trigger A Check Engine Light? 

As @mdttoyotech showed, a loose or damaged gas cap can cause your check engine light to flash. 

Modern vehicles have an evaporative emissions system designed to prevent fuel vapors from escaping. If the gas cap is loose or not sealing properly, the system can detect a leak and trigger a warning.

A loose gas cap isn’t the culprit behind every check engine warning, though. It can start going off for anything ranging from a minor issue to a more serious engine problem, which is why technicians use diagnostic tools and inspections to narrow down the cause.

In the case of the Toyota Tundra @mdttoyotech was working on, he said a visual check helped him quickly find the problem, avoiding unnecessary time spent chasing a more complicated repair.

If a loose gas cap seems like the likely culprit, drivers can make sure it is fully tightened and check whether the cap or seal looks damaged. But the warning light may not shut off the second the issue is fixed. In some cases, the vehicle needs to complete a few normal drives before the system recognizes that the problem is gone.

There is one important distinction: A solid check engine light and a flashing one don’t always mean the same thing. A flashing light can signal a more complex issue, so drivers should consider having their car inspected rather than assuming it’s an easy fix.

Mechanics Agree With Simple Check 

Commenters who watched @mdttoyotech’s video agreed that a quick inspection can save everyone time.

“I’ve gotten [to] a point where if I’ve got a CEL on a car with less than 5-10k on it, my first thought is to check the gas cap in the service drive and move on from there,” one person shared. “Had one a couple weeks ago, and the gas cap fell out when I opened the fuel door, I handed the ticket back to my advisor and told him, ‘void the ticket and clear the code with your pocket scanner.’”

Another said they have dealt with the same problem multiple times recently.

“I’ve had 3 of these this week, all warranty. It’s the worst,” they said.

Others agreed that knowing where to start can make a big difference.

“Easy money when you know what to look for or expect,” one commenter wrote.

“As an advisor, I pull the codes and check the gas cap before writing it up,” another shared. “No point in wasting my time, tech time, or the customer’s time. Happens a lot.”

Motor1 has reached out to @mdttoyotech via direct message on TikTok. We’ll update this story if we hear back.