Common Causes Of a CEL

Hello CTC members. This new Car Talk story is one of a series we are doing that we hope will assist folks with common issues. Much of the wisdom in the stories will come from you, our helpful members who have been answering these questions for other members. Just thought we should give you credit you deserve! Most Common Causes of the Check Engine Light - Car Talk

No mention of how serious a flashing CEL is? That’s a major miss.


#1 Loose gas cap P0457
#2 Catalytic convertor efficiency too low… P0420 and P0430
#3 Misfire P0300, 301, 302… ect
#4 O2 sensor heater circuit… 4 codes for 4 sensors
#5 Lean mix detected P0171 and P0174

edit… I didn’t read the article before I posted this, only after!

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Thanks. I did add that to the FAQs. Could be higher in the text, though, you are right.

Needs to be stronger: If the CEL is flashing or blinking, that means you could be damaging the engine by running it. Get it looked at ASAP, avoid driving it if possible.

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That’s a great article, should be very helpful to car owners w/that annoying dash light staring at them. A couple of additions if you will …

  • If CEL is on, but also flashing, that’s a sign of impending doom, serious engine damage possible, and engine should be shut off immediately and car towed to shop pronto. As long that can be done safely. (As Texas says above.)

  • Don’t make the common mistake of thinking a diagnostic code referencing some part of the car means the first thing to do is replace that part. Most often the problem isn’t actually that particular part is faulty. That part is most likely perfectly ok as is. Replacing it will only introduce another variable into an already complicated diagnosis. Instead the code should be used as a clue for the shop to determine what’s actually wrong.

Thank you, Texases and George! You are right, this was an important part of this story that I overlooked. We jumped right on this and made changes to the story. Take a look and you will see your advice is now part of the piece. Thanks very much! (You may have to refresh the page to see the changes). Most Common Causes of the Check Engine Light - Car Talk

Check out the new version:
Thanks, George!

Looks good!

Thanks GJ for adding the clarifications :slight_smile:

Also to be noted, regular Maintenace will help keep some of those pesky cell lights off.
like air filter changes. As air comes into your engine, it first passes through the engine air filter. Dust, road grime, pollen, and other dangerous contaminants are, hopefully, trapped in the filter. If the engine air filter becomes clogged, some of the pollutants can pass through and hit the MAF sensor. Thus, a clean engine air filter protects your MAF sensor
synthetic oil changes for keeping your engine from getting slugged up.
changing spark plugs, wires/boots according to your owner’s manual maintenance schedule. to keep away those misfires.
Use top tier fuel to keep your fuel system clean. and replace your fuel filter if an option on your vehicle.
On older vehicles check the vacuum hoses for dry rotting or cracking. a small vacuum leak can cause all sorts of problems.
your owner’s manual Maintenace Schedule is a good reference for up keeping your vehicle
Happy Motoring