2005 Bonneville SE 3.8L. Reoccurring EVAP codes:

PO442 EVAP System Small Leak Detected

PO455 EVAP System Leak (Large)

I understand this can be related to something as simple as the gas cap but I have cleaned the metal filler neck well and the codes still reappear. After replacing the engine in my 2002 Buick LeSabre 3.8L yesterday, I'm wondering if the EVAP leak is actually coming from the intake gaskets. There is no visible leakage but with the know history of this engine and EGR/Plenum/Intake issues, would it be wise to just replace the plenum and intake gaskets?

Let me see if I read this right.
Recently you changed the engine?
Now you are getting SES light on with P0442 and P0455 since you had replaced the engine.

Let'* start with the engine. Is this a new crate engine, or a junkyard engine.

Did you have any modifications done to it?

A EVAP code isn't going to come from the engine. You need to check the vacuum lines that are part of the EVAP system. They go from the gas tank up to the engine compartment.

Sorry for the confusion. The vehicle is a 05 Bonneville SE 3.8L stock. It is the one getting the codes.

I also just replaced the engine in my 02 LeSabre (same exact engine) and that one was going through intake gaskets and finally the engine seized up. Even the junkyard engine I bought had leaky intake gaskets which I replaced along with the plenum before installing. Un-related to the Bonneville.

I am wondering if the Bonneville could be getting the codes from a vacuum leak due to leaky intake gaskets.

Thanks for the help!

No, the car will not give a HVAC code because of a leaking intake gasket. Different system.