01 Lesabre "gas cap loose" message

JP

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I keep getting a message on the IP display that the gas cap is loose, which it never is. Sometimes it goes away, but when it doesn't, it eventually sets a code. I forgot the code, but it has to do with the evaporative fuel recovery thingy system.

The gas gauge has also been funky lately; it will read full when full, but as the tank starts to get less full the gauge could read anywhere between full and empty. It doesn't seem to "slosh" when I come to a stop.

My guess is that the fuel cap is fine, but there is a malfunction in the gas gauge sender unit that's leaking air.

Any suggestions as to how to figure this out?
 

Gus

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Those are two completely seperate problems.....

The cap message is there, because you have a leak....the message tellls you to tighten the cap to "try" to fix the problem....if the cap is tight, and the message still comes on, then you have a bad cap, corrosion on the fillpipe where the cap seal mates, or you have a leak elsewhere in the system....

The gas gage problem is usually the level sender...needs to be replaced....
 

JP

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The check engine light went off, and so did the cap loose message. I assume that after so many cycles, if it seems OK to the sensors, it just resets itself. Will the code still be stored if I borrow a code reader and scan it?

Are gas-cap gaskets available, or do I buy a whole new gas cap if I want to try that?
 

kev2

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try a free scan at the parts stores -autozone etc.

you will need a cap no "gasket" available- suggest you keep it tight and wait and see-


you are correct - constant monitor and after X cycles will reset
 

Russ

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Check the mating surface of the gas cap. Good news is that GM put a plastic neck, so they dont rot out. Bad news is that they put a tin wrap around the mating surface that rusts. Your tank relays results of a pressure leak down test and trips your light. Clean it up with a rag stuffed inside, and a brass wire brush. Spray the cap rubber with WD40, and put some oil or 85w90 on the tin. When you change your oil, sevice the cap and tin surface on the neck the same way as I described. Also, your guage is shot. I had good luck getting a used low mileage one for my 2000. Same problem. Closer to empty, the guage was all over the place. You will need the vin# to get the right one.
 

Gus

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How did you come up with his gauge is shot?
 

JP

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I'll try the clean-up first. New caps are pretty cheap, I found, if that doesn't work.

I also noticed that on this model Buick, you don't have to drop the tank to get at the sender unit; there is access through the trunk. I don't know if this is easy to get to...crawling around in the trunk doesn't seem like much fun.
 

JP

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Russ said:
Check the mating surface of the gas cap. Good news is that GM put a plastic neck, so they dont rot out. Bad news is that they put a tin wrap around the mating surface that rusts. Your tank relays results of a pressure leak down test and trips your light. Clean it up with a rag stuffed inside, and a brass wire brush. Spray the cap rubber with WD40, and put some oil or 85w90 on the tin. When you change your oil, sevice the cap and tin surface on the neck the same way as I described.
Done. Seems to be fixed
 

JP

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Dang it. Message popped up again. I'll try a new gas cap.
 

JP

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Replaced gas cap. Same message. What next?
 

Gus

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First, get code read.........

Then get the system smoke tested to find leak.....

Or, just keep replacing parts in the evap system.....
 

JackC

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I am not an expert in this field, so take it for what it is. Others may jump in with better info. Hope this is somewhat helpful for you.
I found this on the WWW.

Now just because you have no leak under vaccum doesn't mean you can't have a leak under pressure.

Another thing that could show that you have a leak is a faulty fuel tank pressure sensor or you can call it a FTP sensor. This sensor is what determines if you have a leak. What the PCM does is close the vent valve and opens the purge valve starts pulling a vaccum, then the PCM closes the purge and looks to see a change in the FTP sensor, no change will store a P0440.

I have seen the fuel sender seal cause a leak and it is hard to pick up using the Evap test station.

The dealer needs to use the flowmeter on the test station to be sure your car has no leaks and that the FTP sensor changes with pressure and vaccum applied.


And another one:

A P0440 Large EVAP leak sets when the PCM does an EVAP integrity test on the system and it fails.
Large leak is a relative term in this case, anything that will allow pressure to escape from a .020” hole, is considered a large leak.
Any time the fuel level in the tank is from ¼ to ¾ full is when the PCM may run a test.
The PCM will turn on the purge solenoid; which will allow engine vacuum to enter the system.
The PCM will also turn on the vent solenoid sealing the vent.
The PCM will now watch the EVAP pressure sensor, which should be showing an increase in negative pressure in the EVAP system.
Once a certain pressure is reached (depending on fuel level); the PCM will turn off the purge solenoid; completely sealing the EVAP system.
Now the PCM will watch the pressure sensor; timing how long it takes for the pressure to leak down.
So if the pressure cannot be reached or if the pressure degrades too quickly; on comes the light and the 440 sets.
Causes could be the purge solenoid, vent solenoid, pressure sensor, vacuum supply to the purge solenoid, wiring, PCM or a leak anywhere in the system, larger then .020” (pin hole).
The purge solenoid is under the hood, the vent solenoid under the car close to the fuel tank and the EVAP pressure sensor is on top of the fuel tank.
The testing is quite simple with the proper equipment; a scan tool to command the solenoids on & off; an EVAP leak test/smoke machine, to apply smoke to the system under low regulated pressure.
The smoke is there as a visual aid, you won’t see gas fumes leaking out of that small of a hole or leak in a line or solenoid.
 
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