Check engine light 99 Grand AM GT

[RandyMcC]

My check engine light has been on for a few months now. The odd thing about this is that it is only on durring the day, and goes off at night. What the heck could be causing this? I took it to a local mechanic and nothing came up on the diags.

Thanks

[RandyMcC]

Could this be caused by something as simple as a blown headlight?

Any info would be great!

Thanks

[Martina]

Originally Posted by RandyMcC

Could this be caused by something as simple as a blown headlight?

Any info would be great!

Thanks

Blown headlights will usually make the service vehicle soon light come on, not the service engine light.

[BBcued]

My check engine light was on in my 98 Grand Am GT for months also and it turned out to be my gas cap. Make sure you have the the right kind of gas cap on (if it isn't the one that came w/car) and make sure it is on secure. This caused all kinds of weird things to happen to my car( wrong cap). The night/ day thing though stumped me.

[lefty13lefty]

It could be the charging system, when the light are headlights are off there is no load on the system when they are on there is a load on the system and it could be causing the light to go out, it could also be the coolant temperature, there is a lower ambiant temp. at night than there is during the day.

[richtazz]

I agree with BBcue. It may be in the fuel vent system. it wouldn't act up at night because it doesn't have the sun beating down and causing excessive vapor build-up in the tank.