Hello everyone,
I thought I'd put this out there as some of you have better access to information than I do.
Can someone with a FSM please scan or post if possible the diagnostic pages with the steps to determine the cause. I've been searching and reading but have found no systematic procedure to troubleshoot this issue - other than to replace the gas cap which I've done with a new GM unit. I am simply trying to find out the necessary steps and how to'* for diagnosis as opposed to just replacing parts.
.....and no I am not overfilling the tank!
Thanks in advance guys and gals - I do appreciate it!

Is it P0452? Have you been using any fuel additive lately?

No additive, why do you ask?

Well, the time I had my P0452 buzzing, I just so happen to have Chevron fuel injector cleaner in the tank. The code was for the fuel tank pressure circuit. So then I changed out the FTP sensor. Well, after installing that and erasing the code, a few days later I had the code back.

Eventually the check engine light went out and never came back. The check engine light would only come on every so often anyway; not all the time. But the most interesting thing is, as soon as I burned up all the gas with the cleaner in it, the check engine light has never came back.

I'm certainly not being that fortunate. I'm glad your issue is solved.

You're going to have to get the car scanned for codes unfortunately. There are different sensors throughout the EVAP system that check for pressure and any one of those will give the "check gas cap" message. On our 00 SSEi it was a bad pressure sensor, like MACDRIVE was mentioning, but it'* impossible to tell which it is unless you get it scanned.
Has your service engine soon light come on yet?

Which DTS code do you have anyway?

As far as trouble shooting the coded circuit; usually it involves checking the reference voltage to the sensor in the affected circuit, then checking the signal voltage going back to the PCM. The signal voltage has to be checked with the the sensor still plugged into its connector by back probing the connector. The key must be on to have the circuit powered up for these tests.

Have you checked out AllData'* free 2003 Bonneville info? There'* alot of stuff on there that pertains to 2000-2005 Bonneville / LeSabre.

Which code is being thrown would be helpful to help pin point the problem. Diagnostics procedures listed in the FSM requires a scan tool. Did you check the vent solenoid from this thread?

http://www.bonnevilleclub.com/forum/...hlight=gas+cap

The code received was P0440. Archon I had not forgotten about that post, in fact I found the vacuum lines by the passenger rear wheel and I got the 'click' while checking it was connected properly. I started to become unsure about which was the vent solenoid because you had mentioned previously 'The last one that I fixed was done by cleaning the vent solenoid by the rear wheel,' however later in the post there is a picture with a description saying it is on the driver side under the rear seat.
I guess I didn't want to seem like a complete idiot so I checked the lines but have no idea how to clean it. The only alternative I could come up with is that there are two vent solenoids then. If this indeed is what I need to replace do I start with the rear wheel or under the rear seat? ...Or, is it the other one in the engine compartment by the rear valve cover (couldn't find that one yet)?
By the way - where is that pressure sensor located please?

Seems out of all the possible codes to get this one is very general and elusive.
P0440 Evaporative Emission (EVAP) System
P0442 Evaporative Emission (EVAP) System Small Leak Detected
P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit
P0446 Evaporative Emission (EVAP) Vent System Performance
P0449 Evaporative Emission (EVAP) Vent Solenoid Control Circuit

Thanks again everyone!

One is the evaporative vent solenoid, the other is the evaporative purge solenoid. It would be easier if they had come up with less similar names. The part about being under the seat was in answer to your question about the other fuse block.

The picture that I posted in the last thread shows its location. It is tucked up where the body starts to rise by the rear wheel, and is under the car. To clean it, you have to remove it, and take it apart. Frankly, I don't recall if it was screwed together, held with plastic clips, or both. Take it apart, clean it up, and lube it with some silicone grease inside, and see if that helps.