Check engine light on a 1996 900SE

From time to time, there are comments about check engine light problems. I have been one of those commenting, since I have had such
problems from time to time during the three years I have had my 900 SE.
    The history of my problems dates back to just after I bought the car. The check engine light came on, and stayed on, after I had owned the car for about four months. I took the car to the dealer on several occasions, and different solutions were tried -- including replacing the oxygen sensor on a trial basis. Ultimately the dealer said the problem was in the wiring, and resoldered some harness. That took care of the problem for about 18 months.
    Then, once again, a few months back the light came on as I was driving. No driveability problems. I took the car to an independent Saab specialist, who said the computer indicated a vaccuum leak, and this likely was a defect in the gas cap seal. I said that during the earlier round of problems I had had the gas cap tested at an emissions testing station, and they said it was fine. The independent mechanic said the testing station's standards weren't high. So I replaced the cap, and the problem went away again.
    Third round of problems. (Wake up, you at the back of the room!) Started about a month ago, when I drove off from a gas station without having put the gas cap on. I noticed the problem soon afterwards, went back to the gas station to retrieve the cap, and the check engine light came on as I was returning to the gas station. The gas cap had been crushed by another car, so I bought a new one. The check engine light went off again after about 20 miles after I had put the new one on. However, on a long trip about a week ago, it came back on again -- for no apparent reason -- and stayed on. I've been driving around with the light on, intending to get it seen to when I had a chance. HOWEVER, yesterday, on a whim I unscrewed the (relatively new) gas cap, and screwed it back on again. The light then went out and stayed out.
    Can anyone diagnose this problem? I'm wondering if, going back to the first occurrence, it was ALWAYS a gas cap problem, although that doesn't explain why the check engine light came on again after a new gas cap had been put on. I very much doubt that it was because I didn't screw the cap on sufficiently tightly at my last fillup. Despite my negligence in leaving off the cap that one time, I am usually meticulous about this since I found about the link to the check engine light. Furthermore, the time the light came on on my long trip, I had driven about 200 miles since the last fillup. So it couldn't then have been because I didn't properly secure the cap after filling up the car.
    Secondly, since the car has 83,000 miles on it, it's likely soon to need a new oxygen sensor. Do I really need to pay $400 for this part (which is what the Saab specialist told me they cost). Also, is putting in a new O2 sensor an easy DIY job?
\\ anrulefr
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wrote:

It does sound like it's related to the pressure switch in the tank. If you could drive to an Autozone store the next time it comes on and have them read out the code that would be helpful. The pressure in your tank could be too high, too low, the sensor could be bad, or it could have a bad connection that causes it to throw errors.

Try www.eeuroparts.com first. I've heard of people using a "standard" Ford sensor to replace the Saab one. You might do a search on this group in google using "Ford" as a keyword. AFAIR, you have to splice the wires for the Ford sensor, but otherwise it is the same. The sensor is DIY but you will possibly need to buy a special socket to fit down on it and around the wires. They sell them at most good auto parts stores. I would not worry about it unless/until you have a problem. They sometimes go many miles without issues.
Bob
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