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EVAP Monitor Ready, Yet CEL is on for EVAP problem

I have an OBD scanner and when I use it, I get a p0455 code which is a code for a large leak. However, when I check the I/M, it says the EVAP system along with all other applicable systems are ready except for the HO2S ( which was ready in previous drive cycles and should be fine. )

I was considering replacing the gas cap because I have an aftermarket gas cap, but I’m also confused that it would say the EVAP system was ready, yet still have a code for an EVAP issue.

Also. If I do replace the gas cap with a Genuine/ Original Quality gas cap, should I reset the code or just drive the car?

I have until October 8th to pass the smog test.

The car is a 2003 Hyundai Sonata GLS 2.7L

I’ve checked the Purge solenoid valve and it was fine.

What’s your make and model I know with out a smoke machine some times evap systems can be pain to deal with but you need to make sure you purge isn’t staying open as well as checking the gas cap

You’re misunderstanding how the readiness monitors work, and what they mean

When the monitor is “ready” . . . that means it has run to completion

It does NOT necessarily mean there are not problems

It does NOT necessarily mean there are no fault codes

Essentially, that code you have means it wasn’t able to pull a sufficient vacuum on the evap system, within the allowable time-frame

here are a few possibilites

fuel filler cap has a bad seal
fuel filler cap wasn’t installed properly
fuel sender seal is torn
fuel tank itself is damaged
evap purge solenoid can’t pull a vacuum . . . often a blown diagphragm
hose from intake manifold to purge solenoid damaged/disconnected

As you can see, there are many possibilities

Is the engine light on right now?

The car is a 2003 Hyundai Sonata GLS 2.7L

& I’ve checked the Purge solenoid valve and it was fine and yeah. the engine light is on.

“I’ve checked the Purge solenoid valve and it was fine . . .”

Please further clarify that statement

For example, just because it’s clicking doesn’t mean it’s working correctly, nor does that necessarily mean it’s pulling sufficient vacuum, or even GETTING sufficient vacuum from the manifold

Is the fuel filler cap seal torn and/or crumbling?

Well I did the test where you try to blow air through and it was sealed/ no air went through.

@Tester (one of the experts who post here regularly) recently posted a good overview diagram of how evap systems are configured. I hope you can see it OP by clicking on the link below.

Taking a look at Tester’s diagram, you can see there’s lots of places for an evap leak to occur. The purge valve is a common one, it gets stuck on sometimes, but it sounds like you’re sure you’ve eliminated that as the source of the leak. So you now have to just go through all the other possibilities one by one. If you could find it like you’d find a leak in a tire – putting it underwater and looking for bubbles – that would definitely make it simpler, but alas, you can’t do it that way with a car. Shops have a sort of similar way as the under-water method to find an evap leak fast, a machine that injects smoke into the top of the gas tank. Then they just look around for where the smoke is getting out. If no smoke is getting out, but the computer says there is a leak, then the next suspect is the pressure (or vacuum) sensor may be bad. So one idea, ask a shop to do a smoke test. They’ll tell you what they find, then you can decide if you want to fix it yourself or let them do it.

Sorry, but I completely disagree with you

The purge valve has not been eliminated at all, IMO

Nobody has yet proved it . . .

is receiving sufficient vacuum from the intake manifold
is receiving the proper signal to do its stuff
is capable of pulling a sufficient vacuum

As I’ve said in the past, a leak code does not mean there is a physical leak

It simply means a sufficient vacuum wasn’t generated

No disagreement, you are absolutely correct @db4690 . From looking at Tester’s diagram it’s pretty clear there’s multiple ways an evap leak condition might be detected by the computer, without there being an actual leak.