About the site

Built by someone who's actually fixed these cars.

Check Engine Light is a reference site written by an ASE Master Technician. Every guide comes from 22 years of working on customer vehicles, not from rewriting other people's content.

MR
Written & reviewed by

Marcus Reid

ASE Master Automobile Technician (L1 Advanced Level Specialist) · Based in Ohio, US

ASE Master Certified L1 Advanced Engine Performance 22 years experience 5,000+ diagnoses
Why this site exists

Most car advice online is written by people who have never held a wrench.

I started Check Engine Light in 2024 after getting fed up with the same recycled misinformation showing up in search results for every code I tried to look up.

You've probably been there. The light comes on, you type the code into Google, and the top results tell you one of two things: either replace the most expensive part the code could possibly indicate, or try ten generic "fixes" that have nothing to do with your actual problem. Half of those articles were written by people who clearly learned about cars from other articles.

Check Engine Light is an attempt to do this differently. Every page on this site is written by someone who has actually diagnosed the problem in a shop. The prices are real prices from real invoices. The tool recommendations come from tools I own and use. When I say a code is usually caused by X but 40% of the time it's actually Y, those numbers come from the log of jobs I've done, not from someone's blog post citing another blog post.

The goal is simple: give you enough real information that you can either fix the car yourself, or know whether the shop quoting you $1,500 is being honest.

Credentials

Who's actually writing this.

ASE certifications are independently verified by the National Institute for Automotive Service Excellence. You can look up any technician's credentials on their public registry.

A+

ASE Master Automobile Technician

Issued by ASE · 2008

The full A1–A8 series covering engine repair, automatic transmission, manual drivetrain and axles, suspension and steering, brakes, electrical systems, heating and air conditioning, and engine performance. Renewed every 5 years through continuing education.

L1

ASE L1 Advanced Level Specialist

Issued by ASE · 2011

Advanced Engine Performance Specialist certification. Covers OBD-II diagnostics, computerized engine controls, emissions systems, and the kind of deep diagnostic work that a regular A8 Engine Performance cert doesn't get into.

EV

Hybrid / EV Specialist Training

Toyota TIS & ASE · 2015

Toyota Technical Information System training plus ASE xEV Safety recognition. Qualified to work on hybrid and EV high-voltage systems safely. Not required for writing about CELs on gas cars, but relevant as the vehicle fleet evolves.

By the numbers

What 22 years looks like.

22
Years wrenching
5,000+
Diagnostic jobs
3
ASE certifications
500+
Invoices in our DB
Editorial standards

How content gets made here.

Every article on this site goes through the same process. No AI-generated filler. No "ultimate guides" written by freelancers who've never opened a hood.

01

First-hand diagnostic experience

Every code and repair covered on this site is something I've personally diagnosed and fixed on customer vehicles. If I haven't done the job myself, I don't write about it. The site covers about 40 of the most common OBD-II codes because those are the ones I have real data on, not because 40 is a round number.

02

Prices come from real invoices

The repair costs on this site come from an anonymized database of roughly 500 invoices from my shop and other independent shops I network with. When you see "$150 to $350" for an O2 sensor, that is a real range of what people actually paid, not a made-up estimate.

03

No affiliate links on tool recommendations

When I recommend an ANCEL AD310 or a BlueDriver scanner, there is no Amazon affiliate kickback behind it. Those are the scanners I own and use at my shop. If I start taking affiliate money in the future, I will disclose it clearly on every page it appears.

04

Reviewed quarterly, updated when facts change

Every guide gets reviewed at least every three months. When a code definition changes, a part price moves significantly, or a manufacturer issues a recall that affects the diagnosis, the page gets updated and the "last updated" date at the top of the article reflects the change.

05

Opinions are clearly labeled

When I tell you to walk out of a shop that quotes you for a cat without testing the O2 sensor first, that is my opinion based on 22 years of seeing that exact scam. It is clearly labeled as an opinion. Facts are facts. Opinions are opinions. The site does not blur the two.

06

Transparent about what we don't know

If a code is rare enough that I've only seen it a handful of times, the article says so. If a manufacturer-specific issue only applies to certain model years, we name those years. Guessing is worse than saying "I don't know, here is who to ask."

Career timeline

How I got here.

2003
Started as an apprentice
Took a job changing oil at an independent shop in Ohio during high school. Worked my way up to brakes, suspension, then engine work over the next three years.
2006
First ASE certifications
Passed A1 (Engine Repair) and A8 (Engine Performance) on the first attempt. Started handling my own diagnostic cases in the shop.
2008
ASE Master Technician
Completed the full A1 through A8 series. Moved to a Toyota dealership as a line technician to work on more complex diagnostic jobs.
2011
L1 Advanced Engine Performance
The advanced diagnostics certification. This is the one that matters most for CEL work. Probably 1 in 5 working techs has this cert.
2015
Hybrid & EV certification
Toyota TIS training plus ASE xEV Safety. Started seeing more Prius and hybrid Camry work come through the shop.
2019
Opened my own shop
Left the dealership to open an independent diagnostic-focused shop. Specialized in the cases other shops give up on.
2024
Started Check Engine Light
Launched this site after years of customers showing up with wildly wrong advice from the internet. Figured I'd publish what I actually tell them when they ask.

Have a question I haven't answered yet?

Email me directly or use the contact form. I read every message and respond when I can.