I need some help..

I have a red dash warning light on..

CHECK ENGINE...

the car sounds and is driving great. no changes at all.


but I noticed when engine running, under the hood, a small red light on, I have no idea if it is related, or what the hell it even is?

its a big black plug on the sidewall located about even with the wheel it has 8 little lights. and # 4 is lit..

can anyone help me out? I want to avoid the $$ deal if I can


thanks

Matt