2004 lexus es330 Vsc, trac, and check engine lights all came on at same time
Already replaced gas cap that I purchased from dealer. If I'm
not mistaken they came on right after having the timing belt
Have to start by having the vehicle scanned for trouble codes. Then you would know what to look at.
Go to Pep Boys or Auto Zone and they will scan it for free. Sometimes the issue is the O-2 sensors...not to expensive if you do it yourself, but a real PITA to change out the rear one.