A Common Misconception?

We’ve had a number of posts along the lines of “my check engine light is on, I checked the gas cap and it’s ok, what else can it be”? Do people really think that’s the only thing that sets the MIL? Where do they get this stuff?

There was a TV advertisement for a low cost code reader. That was the example the advertisement used.

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Maybe they got the information from their owners manual.
This is from the owners manual for the vehicle I am working on right now;

■If the malfunction indicator lamp comes on while driving
First check the following:
●Is the fuel tank empty?
If it is, fill the fuel tank immediately.
●Is the fuel tank cap loose?
If it is, tighten it securely.
The light will go off after several driving trips.
If the light does not go off even after several trips, contact your Lexus dealer as soon
as possible.


And it says nothing to the effect of " this could also be an indication of a more serious problem. If the light remains on, see your dealer as soon as possible"?

lol my mother literally asked me this very question yesterday. I told her- yeah, it could be the gas cap, but it probably isn’t.

Got the Service engine soon and the P0440 code read by Autozone a couple of years ago, got a new gas cap from the dealer and it went away, 2 years later it came back, tried a new gas cap again, no good. No emissions test till june, if the 03 makes it till then I will get it fixed. So yes I got the code was commonly caused by a gas cap, in my case the first time it was.

As car design continues to progress there’s more and more sensors, gadgets, and gismos, so a lot more ways it can fail and turn on the CEL. Maybe in the early days of OBD II replacing the gas cap on a guess would have a reasonable chance of fixing the problem & turning off the CEL. But these days, not so much.

The owners manual statement that I posted was from an old 2014 Lexus ES300h Hybrid, it is nearly as complicated as the new cars.

Vehicle manufactures don’t want to frighten their customers to the point that they have the vehicle towed and set off on foot for simple malfunctions, cars are driven to shops with the check engine light on most of the time.

There are a few cars that actually TELL you to check the gas cap. Apparently it is so common, the car makes the suggestion now. Probably cuts down on trips to the dealer within the warranty period.

Maybe that is why Ford eliminated gas caps. You can’t leave it loose or leave it behind if there isn’t one.