2001 Bonneville

[truc0011]

So the gas gauge stopped working correctly over the winter and now in addition to that the DIC is telling me "Check the gas cap". I put a new GM cap on, the filler neck was rusty so I sanded it and applied some oil to the lip of the neck and the cap.

DTC code is 440 and I keep getting informed to check the gas cap.

Has anybody had these failures be related or are they two separate issues? The car has 120k miles on it.

[maxwedge]

Any gross leak in the evap system can cause this code, the most common issue is the gas cap, barring that unless you find a broken/disconnected hose in the system you will have to have it checked on a smoke machine.

[Tech II]

Yes, they are two separate problems....

The gauge not working is usually the fuel level sender in the gas tank.....I believe it is accessible in the trunk under the carpet trim......you will see a silver panel for access to it......remove it, disconnect the fuel lines, the electrical harnesses......remove the locking ring.....whole fuel module comes out and you can just replace the sender....

Like I said this is the usual problem.......only way to know for sure is with a variable resistor...40 ohms is empty, 140 oh ms is 1/2, 240 ohms is full....

As for the P0440, that is is a small leak...once again the usual fix is the gas cap, next is the vent solenoid, then purge solenoid, then leaking EVAP line, etc...

As Max said, the only way to accurately find the leak is by sealing the system and pressurizing it with a smoke machine....

[rkvons]

Originally Posted by truc0011

So the gas gauge stopped working correctly over the winter and now in addition to that the DIC is telling me "Check the gas cap". I put a new GM cap on, the filler neck was rusty so I sanded it and applied some oil to the lip of the neck and the cap.

DTC code is 440 and I keep getting informed to check the gas cap.

Has anybody had these failures be related or are they two separate issues? The car has 120k miles on it.

At the bottom of your filler neck there is a rubber hose. This rubber hose connects to the gas tank and is fastened to the filler neck by a hose clamp. I think you will find that the surface of the filler neck covered by the rubber hose is severely corroded and is the cause of your leak. You should take the filler neck loose from the hose and see. But if you do that, you should disconnect the rubber hose from the tank. Otherwise a lot of grit will fall into the tank. You might be able to clean up the surfaces of the filler neck and rubber hose and put it back together, but I would replace it with a new filler neck, or one from a junk yard that is decent.

[Tech II]

RKvons, it could be there, but wouldn't you see/smell it in that area? That would not be high up on my list.....have seen the whole fill pipe rusted bad in some cases, just not at the clamp....generally, when you see the fill pipe rusted bad, the whole underneath of the vehicle is bad......

[rkvons]

Originally Posted by Tech II

RKvons, it could be there, but wouldn't you see/smell it in that area? That would not be high up on my list.....have seen the whole fill pipe rusted bad in some cases, just not at the clamp....generally, when you see the fill pipe rusted bad, the whole underneath of the vehicle is bad......

I believe the leak can be enough to fail the test, but small enough where you won't smell any gas. And on my Grand Prix, it failed that test. When I took it apart, the inside of the rubber hose was basically clamped to powder from the rusty neck. I had to carefully clean the inside of the hose out so it would not leak on the new filler neck. I've fixed two of my vehicles that failed this test. If my understanding is correct, the fuel tank is never really under pressure. During normal operation and testing, it is under vacuum. When it is sitting in a parking lot, any pressure goes through the charcoal canister. So to be able to smell it, it would have to be a large leak. And that's a different test. And as far as the whole underneath of the vehicle being bad? True.

[Tech II]

Yes, here in NE, road salt wrecks havoc with the underside of a vehicle....

With all the smoke tests I have done, if it's not the cap, more often than not, it's been the vent solenoid on C, H, and W cars......a smoke test is the only true way to find these leaks.....you seal the system, and pressurize with smoke....easy ,peasy, lemon squeezy.....but only shops have this machine....

Not that I haven't seen rusted fill pipes.....just not a lot of them.....