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Loose Gas Cap Check Cap Comes up in the information center
silverstarr
Member Posts: 1
I have a 2005 Buick LaSabre, V6 My information Panel Reads Loose Gas Cap, I replaced the gas cap 1st with an aftermarket cap, Had the code cleared, recently I am getting the same message so I went to the Buick Dealership and purchased an OEM Gas Cap and was told it should reset after 50 to 60 miles driven. I took my car to a repair shop explained the issue and they reset the computer, the message was cleared, after driving my car about 27 miles, I am getting the same message, loose gas cap, Check Cap, I was told the problem is with the emission system, anyone had this problem, or have any suggestions on where to start to resolve this issue?
0
Answers
If that doesn't fix it, the most likely cause is a defective vapor canister purge valve, it's on the front of the top of the engine, under the beauty cover. Beauty cover comes off by twisting on the stem of the oil filler below the cap--whole thing turns and screws out, letting the gray cover come off. Carefully check the vacuum tubing there from the purge valve to the engine connection. It may have deteriorated with heat and cracked.
That purge valve sits in a very hot area. It's about $25 from Rockauto.com
It is easily replaced if you're comfortable around the fittings. Just look carefully at the connectors to decide how they come off.
If there are no leaks in tubing there and purge valve doesn't fix. Then you go to the vent valve under car under rear passenger's side. There are larger tubes from the gas tank to it which may leak. Or that valve might be bad, but not as likely as the hot, abused purge valve.\
For the emissions test, the purge valve opens to apply vacuum to the tank to see if system is leaking air in. The vent valve is closed to seal off the tank vent through the carbon canister; it's usually open to let air in. Then the pressure sensor on fuel tank pump area measures the vacuum to see how fast it drops. Too fast, and it sets the appropriate code and after two failures, it sets the light.
I had to seal up the leaking "U" on the rubber tube from purge valve to intake manifold over at the throttle body end. It had cracked. Later I replaced the vent valve, and that wasn't the problem. The purge valve apparently was staying open after applying the vacuum, at least partly, and upsetting the vacuum test.
The shade tree mechanic who loves the 3800's GM has used for years, said he just replaced the purge valve first. If car has lots of miles, if valve hasn't gone bad it will go bad. And usually it fixes the problem other than check the soft rubber tubes to be sure they're not rotted.
Sorry my answer is so long, but I went through this over a period of a year and half from first symptom.
BTW, you can drive the car fine despite it's not having passed the test. It is not going to hurt anything from what I can tell.
Good luck.
2014 Malibu 2LT, 2015 Cruze 2LT,
One of the other tests that the system runs is the purge valve leaking test. By closing the purge valve, and then opening the vent valve the system will balance at atmospheric pressure. Then the vent valve is closed and the pressure sensor monitored for a change and if the system pulls into a vacuum, then it is proven that the purge valve is leaking and that sets a code P1441 in most cases.
The "check gas cap message" is generated by the system when it see's a change in the fuel level in the tank which indicates a refueling event and that triggers an immediate large leak test to be run which based on the code setting is failing. A problem with the fuel level sending unit that isn't resulting in a trouble code could contribute to this issue.
tank is below 85%. So a full tank should run an emissions check until the level drops with use.
It does require fuel level between 15% and 85% and requires engine temp roughly between
40 deg F and 100 deg F. Also requires engine intake temp and coolant temp to be within
9 deg F of each other. And some other requirements have to be met.
It would be nice if I could have a Tech II or equivalent tool with which to turn those
various devices on or off to do a logical elimination of parts. But the scanner I have can
command the computer in the car to run the test. I have to hope it runs the test and
eliminates or sets the code again.
Interesting about being able to test the purge valve for less than full closure with
the Tech II. I have one code set for blocked vent valve or something, so I condemned
the vent valve and replaced it first. The shade tree mechanic next door replaced the
purge valve first and sometimes said he just replaces both. Comes out a whole lot
ahead of taking the car to the shops and paying a diagnostic fee AND then paying
a markup price for the parts, often from an aftermarket supplier.
I could have mentioned looking at the surfaces of the filler tube and the connectors
for the tube to the tank. But those rarely have gone bad based on anecdotal reports
from Bonneville and leSabre owners who are knowledgeable about doing or
tracking their own repairs.
For $25 and $20 for the purge and vent valves respectively, I took the replace
parts route. My dealer charges $89 for connecting the Tech II and most
shops in area, if they have one, charge about the same from what I can
tell. A lot of shops don't use the computer and analyze based on experience
and references about what parts are most often at fault, if any, for certain
codes on certain cars. One of the code scanner companies advertises that
their device uses the internet data in that way.
I was able to put my car on wood blocks under the tires to raise it and
support the car besides to work under to get at the back vent valve. If I weren't
able to do that, I would have had my shade tree guy next door do the solenoids
for me one at a time. Then if that didn't work, I would have taken it to a dealer.
Neighbor has been worth his weight in gold, if not for helping, for loaning me
high quality tools to use for my own hub replacement work, e.g..
2014 Malibu 2LT, 2015 Cruze 2LT,
Part of what you wrote above, especially about the fuel level limits actually refers to the requirements to run the evaporative monitor. The monitor enable criteria, which overlaps individual code enable criteria make sure that the tests are run under as controlled of conditions as can be achieved so that the engineers can get repeatable results. The loose cap test isn't part of the monitor so it doesn't need to meet all of the same criteria, but it does rely on previous results from when the monitor ran the last few times for the software to make a decision. Essentially the system see's the refueling event so it commands the large leak test to run, and in some cases they also run the medium leak test. Then the software compares this result to previous test results. If there were no leaks detected previously, but there is now a detectable leak the logic is that the cap might be loose. If there were previous results of a leak and the large leak test fails, then the system re-codes for a large leak and suspends the rest of the testing.
This leads to a very important point, which is usually made by starting with a question. "What is a trouble code?"
The answer is a trouble code is the identification number of a test that failed. Once you understand that, then you learn that when faced with a trouble code it is the responsibility of the person getting ready to do diagnostics to know (or find out) exactly how the computer ran the test that failed and then he/she needs to test the system or circuit themselves the exact same way that the computer did and they will solve the situation efficiently and the first time, without tossing any unnecessary parts.
Lets take a look at P0440, which is often listed as Evaporative System Failure, or A Large Leak or The Weak Vacuum Test. This is the test that runs after a refueling event. This a straight forward test where the system commands the vent valve closed and the purge valve open. The system pulse width modulates the purge valve and depending on how fast the vacuum does or does not build the PCM will vary that command. If the vacuum is building slowly or maybe not at all then a longer pulse-width command should result in a stronger vacuum pull. The PCM monitors the fuel tank pressure sender and looks for the vacuum generated to reach -8" in water. If it cannot pull that much vacuum, the test fails. If it does pull that much vacuum, the weak vacuum test (large leak)passes and the system would then move onto the next test if the monitor is running.
Something typically missed by those who have never really studied how this all works is the progressive nature of OBDII testing. Certain tests have to run and pass in order to allow other tests to run and it is all happening in a prescribed order. Techs always have to remember that when certain tests fail, they block other related tests from running. That's why its important to retest the system in the shop after a repair is made in order to make sure that another code that was blocked from running doesn't turn around and cause the MIL to come right back on.
The FSM lists the codes which cannot be already set in order for each code to be tested.
The summary of the emissions in FSM leSabre 2003 states that the test message about the
gas cap is turned on for a "malfunction in the EVAP system and a large leak fail" and for
"malfunction in the EVAP system and a small leak fail"
So I'm thinking the system on my 2003 is a level below running the test when it's filled up.
The 2005 leSabre may be different.
Having all the fancy equipment to test would be nice. I'll bet 99% of the independent garages here don't have that for most cars.
2014 Malibu 2LT, 2015 Cruze 2LT,
"I'll bet 99% of the independent garages here don't have that for most cars."
So why don't they? Better yet if they haven't been in the habit of tooling up to that level and getting the kind of training that would have them able to explain the systems with as much detail as they really need to be able to, what is going to happen to them when the 2015's and 2016's are eight year old cars? (not to mention the 2010's and newer).
Earlier you mentioned your shade tree guy, he's running a shop so call him one even if he is running it in an area that isn't zoned for a business, or paying taxes on the sales and income, or insured, or, or..... He's no different than a lot of the shops that are just going through the motions hoping to hang on long enough to make a living until they retire as the technology in the cars continues to overwhelm them. Why else would he need to just change both parts and hope that he actually fixed the car? A lot of shop managers are finally learning that competing with your neighbors shade tree shop has hurt them in regards to dealing with the newer cars. By not charging for diagnostics, they also didn't pay the people to perform diagnostics and that's how a lot of the shade tree guys came about. Many used to be techs who left the trade for other careers but still like working on cars and making money for doing so. But most of them are stuck exactly where they were at when they left the trade. They haven't been to training classes, they haven't spent the money to have the right tools and that leaves them trying to pick just the lowest hanging fruit along with a good number of shops who's business plans are evaporating right before their eye's.
But what about the 1% ? The guys/gals who bought their TechII's, and DRB3's, Techstreams, IDS, HDS, etc? The ones that went to training and still do on a regular basis? Maybe if there wasn't so much of an attempt to claim that they were taking the wrong approach there might be more people who would have followed their lead.
After week and half light came back on, in Columbus, and then went off. The light had been on and off a total of 5 times. Seems related to our 0 to 10 deg drawn out cold snaps. The valve contains a pressure sensor. Do you have an opinion about whether it's the valve with the built-in pressure sensor acting up? On internet someone even suggested a cracked head or exhaust manifold causing the problem due to injecting cold air at cold start.
Dealer kept it 2 nights when he let it sit out in the cold to try to get some part to malefunction when he started it.
2014 Malibu 2LT, 2015 Cruze 2LT,
Keeping the car overnight and using the scan tool to take a snapshot of the test running is the right approach. The test runs in three stages for approximately 20 seconds in each phase. During phase 1, both the AIR pump and the solenoid valve are activated. Normal secondary air function occurs. Expected system pressure is 8-10 kPa above BARO. During phase 2, only the AIR pump is activated. The solenoid valve is closed. Pressure sensor performance and solenoid valve deactivation are tested. Expected system pressure is approximately 15-22 kPa above BARO. During phase 3, neither the AIR pump nor the solenoid valve is activated. AIR pump deactivation is tested. Expected system pressure equals BARO.
Once it is proven which portion of the test is failing, then pinpoint testing is performed to prove why it failed. One note, a noisy air pump is associated to a failure of the control valve because of the corrosive nature of the exhaust gasses and the condensing water vapor that condenses in the feed pipe.