# EVAP Monitor Ready, Yet CEL is on for EVAP problem **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** hyundai, sonata\ **Created:** [September 29, 2016, 6:50am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887 "2016-09-29T06:50:34Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Thunda101](https://avatars.discourse-cdn.com/v4/letter/t/258eb7/32.png) [@Thunda101](https://community.cartalk.com/u/Thunda101)\ **Post date:** [September 29, 2016, 6:50am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/1 "2016-09-29T06:50:34Z")
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. EDIT: The car is a 2003 Hyundai Sonata GLS 2.7L I’ve checked the Purge solenoid valve and it was fine. ---
**Author:** ![Rj\_jr](https://avatars.discourse-cdn.com/v4/letter/r/22d042/32.png) [@Rj\_jr](https://community.cartalk.com/u/Rj_jr)\ **Post date:** [September 29, 2016, 9:23am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/2 "2016-09-29T09:23:46Z")
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 ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [September 29, 2016, 4:28pm UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/3 "2016-09-29T16:28:15Z")
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 etc. As you can see, there are many possibilities Is the engine light on right now? ---
**Author:** ![Thunda101](https://avatars.discourse-cdn.com/v4/letter/t/258eb7/32.png) [@Thunda101](https://community.cartalk.com/u/Thunda101)\ **Post date:** [September 29, 2016, 8:51pm UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/4 "2016-09-29T20:51:29Z")
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. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [September 29, 2016, 10:04pm UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/5 "2016-09-29T22:04:51Z")
“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? ---
**Author:** ![Thunda101](https://avatars.discourse-cdn.com/v4/letter/t/258eb7/32.png) [@Thunda101](https://community.cartalk.com/u/Thunda101)\ **Post date:** [September 30, 2016, 1:10am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/6 "2016-09-30T01:10:13Z")
Well I did the test where you try to blow air through and it was sealed/ no air went through. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [September 30, 2016, 1:30am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/7 "2016-09-30T01:30:27Z")
@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. > [@Having troubles starting my car, mostly after pumping gas!](https://community.cartalk.com/t/having-troubles-starting-my-car-mostly-after-pumping-gas/95831/8): > > The problem might be with the purge valve in the EVAP system. This valve is normally closed. But if the valve sticks open, fuel vapors can be forced into the engine while refueling, and this can cause a flooded condition where it requires that the accelerator be depressed in order to start the engine. Since the advent of OBDII, it’s impossible to flood the carbon canister in the EVAP system on today’s vehicles. Because not only does it have roll-over valve, it also has a refueling control valv… 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. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [September 30, 2016, 1:39am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/8 "2016-09-30T01:39:35Z")
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 ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [September 30, 2016, 1:59am UTC](https://community.cartalk.com/t/evap-monitor-ready-yet-cel-is-on-for-evap-problem/95887/9 "2016-09-30T01:59:02Z")
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.