Had car for 30,000 miles. Since I have it the check engine light is on. Everytime they reset it, it goes on the next day or within hours. The Volvo center insisted each time but last that I was putting the gas cap on incorrectly, based on the computer printout. Believe me, I'm putting it on correctly - I have the same mechanism on my Z3 with no problem.

The last time I brought it in they finally said it wasn't me that it was the battery spiking causing the sensor to erroneously trigger. They gave me a brand new battery and naturally the next day the light went on again.

The second problem I think is related, but not sure. Again since I got it - whenever I fill the tank (I don't top off) the car stalls or hesitates within hours of driving. It will clear up when the gas drops. If I don't go past 3/4 fill I have no problem.

Any help would be appreciated.

Hi Russell,

It sounds like you need to find a Volvo Center who knows how to fix an S80 gas tank.

From your description it sounds like you have a problem with the gas tank purge system. Gas tanks are not what they use to be in the old days. Due to emission and pollution issues gas tanks are designed not to allow any gas fumes into the atmosphere. Therefore, they are closed system. This means that when the engine consumes gas the air required to replace the consumed gas is controlled. So when you leave the gas cap off or the gas cap is not installed correctly the check engine light comes on.

What I believe is your problem is that the gas tank air control system has a problem. This would explain why when you have a full tank of gas the engine does not run correctly. A full tank has no space for air. When the gas is consumed the system that allows air to replace the consumed gas is not working. This causes the fuel pump to work harder in supplying gas to the engine. When the vacuum due to no air replacing the consumed gas reaches critical the fuel pump can not longer supply gas to the engine. Hence your hesitation. When you have a gas tank ½ filled you have a tank ½ filled with air. Therefore, that critical vacuum required to slow down the fuel pump is harder to reach (the gas tank can collapse). This is why you do not see your hesitation when the gas tank is ½ full.

I would suspect that you have a problem with the following

1) Computer air control valued is not working
2) Wiring problem. Possibly a bad connector
3) A kink in a hose

The Gas Tank System needs to be fully inspected and tested. Not an easy job! This may require the gas tank be removed from the car. This is why I suspect that your Volvo Center is doing what they are doing. Reset the Check Engine Light and send you on your way in hope that problem will not come back (i.e. you will not come back).

The next time you go back stick your index finger in their noises and tell them you want it fixed. There is no excuse for a Volvo center not to know how to repair a S80.

Good Luck,

Steven---

The check engine lamp comes on any time a fault code is recorded relating to anything that could affect the emmisions output. The list is long and the only good starting point is reading the fault code(s). Assuming you are dealing with qualified Volvo technicians, I would insist they keep working at finding the problem. I'm puzzled that they seem to be having a problem....the fualt codes are usually pretty accurate in nailing down the source. You may have to start looking at other areas that do not generate codes, but at the same time could affect the emmisions...