Is this true what mechanic told me?

[Frosty Power 323CI]

Went to the dealer yesterday and got them to check out my check engine light. Apparently they said it was because of my gas cap, so they replaced it and it went off. Anyways, I was talking to one of their mechanics there, and he said if the check engine light is on, all their cars will not run at it's best mechanically, even if there is nothing wrong with it mechanically. meaning it would run in some sort of "safe mode" and not run 100%, even if it it just the gas cap. Just curious if this was true or not, but I did notice a slight difference afterwards, but maybe it was just in my head...


Thanks,
Frosty Power 323CI

 

[Big Daddy]

Leaving a gas cap off, or installed improperly will cause a "check engine" light to activate. I am not sure about the mode the car will operate in but the argument makes sense.

 

[j2azz]

It could cause it to operate safely since the fuel tank isn't venting properly. Might make the car run rich or something..

 

[MrElussive]

That definitely does make sense because sometimes that Check Engine light can signify a pretty big problem, but the car is still drivable so it runs more "gentle" so as not to harm itself.
It could be one or more of these things:
-Engine doesn't allow for full throttle
-Engine redline lowered slightly
-Engine timing (ECU) adjusted for less power

 

[Frosty Power 323CI]

Yes, I certainly did notice a difference. Whether its just me or it actually is the car. Did any of you guys notice any differences? Power wise? Before check engine light was on then switched off?