I couldn't find this issue dealt with when I searched this website, so I wanted to bring it to the attention of other 2000-2005 Lesabre owners. Back in June 2011, I bought a used 2001 Lesabre with 77k miles and on the drive home the check engine light illuminated and I got an intermittent "gas cap loose - check cap" message on the DIC. My code reader showed both P0440 and P0442 codes, indicating large and small leaks, respectively in the evap system. I reset the code and installed a new GM gas cap and in about a week the check light reappeared with the P0442 code with more intermittent "check gas cap - check cap" DIC messages.

Upon a detailed test of all of the evap components using an improvised diaphram vacuum pump, I isolated the problem to a loose metal flange in the fuel filler tube. This was surprising, as the mileage was relatively low. After reading several horror stories on the internet regarding the difficulty in properly diagnosing small evap leaks without smoke generator equipment, I was happy I found the problem. However, this was quickly lost when I got the cost of the replacement part from my local GM dealership of $427 (Part No. 25727011)! I was told the cost to have this replaced by the dealer can be over $750!!!!!

To avoid this outrageous cost, I attempted to reapply force to the four metal tabs but in my case the gas cap flange still leaked due to deterioration of the o-ring gasket under the flange. I then attempted to remove the flange from the filler but because of a rivet to hold the filler restrictor, it would have been destroyed and unrepairable if the rivet was removed. Being an extreme DIYer and having a Master's in the art of JB Weld, I was able to successfully fix the part for about $1 in epoxy material. I believe this problem is significant in numbers and any other owner should consider a repair to their current filler tube rather than purchase another poorly designed new one. You will need to remove the filler from the car and then where the metal flange makes contact with the plastic filler, apply to the circumference the JB Weld and in the four metal tab holes. To get maximum penetration, I applied a vacuum with an improvised hose and when the JB Weld was pulled into flange I reapplied it a second time until the epoxy was coming out of the four tab areas and the inside flange area. This has fixed the problem for the last two months. I now wish I took pictures but at the time my attention was focused on the repair.

Obviously, this design with the combination of a steel flange to a plastic part is defective. The process of applying counterclockwise (removal) and clockwise (tightening) of the gas cap puts too much strain on the plastic filler and wears a groove to the point the flange loosens. I far I can tell this design is only present in the Lesabre and the Pontiac Bonneville of the 2000-2005 vintage.

I thought this website was the best way to provide my information of this relatively easy fix and I hope that other members can apply it successfully.

 

Concerning the P0440 and P0442 codes I had the same problem wiith my 2001 LeSabre, and tried a few things to no avail. After reading about how you fixed yours, I decided to try and fix mine. Before going through the process of removing the fuel filler pipe I bought a tube of permatex silicone sealer at Walmart for about 4 dollars. I reached under the fender well, and found the flange by feeling. I put the silicone on my finger and sealed all the way around. I used the silicone on a couple of areas of the filler pipe, and also inside the fuel door on the grommet and tab holes etc. I have gone about 1000 miles so far, and all is well. I have 118,000 miles on the car, and the problem started at around 100,000. Thanks for your tip, and I hope my problem is solved.

 

Thank you guys for sharing that info with us !

 

I have a 2003 Buick Limited LeSabre and I'm getting the "Gas cap loose; check cap" message. This thing starts for about a day and disappears for about three days and then does it again with a p0440 code. I replaced the cap with a dealer gas cap ($30.00); the message stopped almost immediately. Friday last, I started my car for the first time on that day, and guess what...!!!
Sunday, I read your post and decided to check out this gas tank filler neck by twisting it a little. There is a rubber sealing ring that goes around the filler neck. I hope someone on here (if not you) just happens to come across this post and help me out.

 

Eventually the silicone sealer on the fuel filler pipe developed a leak or leaks? This happened at near 2,000 miles after it was put on. When the light came back on and the message appeared I knew what it was for sure. This time I removed the fuel filler pipe and removed the silicone sealer that was still there. I mixed up some JB Weld and put that all around the flange where I had the silicone sealer before. Don't be afraid to use a lot of it and cover everything good. Let it dry a couple of hours before putting it back on. It has now been over 30,000 miles and no problem and no leaking. Hope this helps you out. Easy fix. Not expensive.

 

I’m glad my original posting of this problem has been a help to others.. Based on your description I think the steel flange of the filler neck has loosened and causing your intermittent check DIC “Gas Cap Loose” message. You’ve already ruled out a defective gas cap and gasket with the new gas cap replacement. My suggestion is to remove the gas tank filler tube and do the repair I did. There’s an aftermarket filler from Spectra Premium (PN FN798) but it’s listed at $326.79 on RockAuto. It still has the defective plastic to steel flange design and will probably fail again but may outlast your car. My repair with the JB Weld has lasted for almost four years without any recurrence of the problem. I also want to caution you that a leak somewhere else in the EVAP system could be causing your problem and if so, these will produce the DTC 0440 and P0442 codes.

 

I found a rubber sealing ring around where the fuel cap goes. I tore it up trying to remove it; was this the piece Buick lesabre owner speaks of? In another attachment I am holding the fuel filler tube with my finger pointing to where I think I found the leak (is it). I put the gas cap on, and then blew into the other end of the filler tube and the leak I suspect is where my finger is. Is this the notorious leak? I found the four tabs by the way.

 

[QUOTE=2001 Lesabre Owner;11506]You will need to remove the filler from the car and then where the metal flange makes contact with the plastic filler, apply to the circumference the JB Weld and in the four metal tab holes. To get maximum penetration, I applied a vacuum with an improvised hose and when the JB Weld was pulled into flange QUOTE]


Can you stuff the JB Weld into the tabs? Did you use the stuff that has two compounds that you knead together before applying?

 

I didn’t bother trying to remove the rubber gasket under the steel flange, as I didn’t want to break the tab for the ground wire. The best way for you to do this is put the filler upside down where the steel flange is resting on a flat surface and pour around the circumference the JB Weld (two part standard mix formula) and let it drip down to the flange and the plastic filler tube. You will need to make repeated applications as the JB Weld will travel and you want to keep applying to the point where it doesn’t disappear and leaves a smooth bead around the outer steel flange and the inner plastic. I used a vacuum pump with a hose attached to a flat piece of rubber to help draw the JB Weld into the cavity faster but you don’t need to do this. I also used tape on the bottom steel flange to keep any seeping JB Weld excess off the mating surface. You need to make sure to remove any and all JB Weld from the flange where the gas cap tightens before it takes a hard set. If you don’t the gas cap can’t be tightened properly.

 

George: The leak I had on my LeSabre fuel filler pipe was all around the small raised portion of the pipe where the ground wire is connected to the pipe. That's where I used the JB Weld. I found that leak by filling the pipe with water. Blocking off the large end and blowing into the small end I could see the bubbles forming all around the raised portion of the pipe. Hope this helps. It's possible your leak is in a different location?