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Check Engine - Faulty Gas Cap??? C70 1999

Hello,

Recently, my check engine light has been acting up. The first time it lit up (about half of my tank was used up), I thought it might be the gas cap. I unscrewed the cap and re-screwed it back on. About couple hours later, the check engine light went away. However, the next day, the light went back on. I needed the car the rest of the week, so I didn't have time to take it to a dealer.

When I had little gas left, I went to fill the tank up. As soon as I started the car, the check engine light went away again. This time, it went away until half a tank again...then the light went back on. At this time, I started to think that maybe there was something wrong with the gas cap. So before I did anything, I decided to experiment this some more.

The next week, I went to fill up gas again to full and the light went away. Then, halfway thru again, the light goes on.

Do you think this might be because of a faulty gas cap? The dealer told me before that when air gets into the tank, the check engine light goes on. Maybe that would explain why everytime I fill up the tank, the light goes away (due to less air in the tank.) Has anyone else had this problem before?

Thanks!!








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    Check Engine - Faulty Gas Cap??? C70 1999

    O2 sensor? What is this used for?

    Sorry, I'm not a parts expert. Is it really necessary to replace this part. I mean, everytime I fill up, the check engine light goes away. It's just after 100~150 miles, the light comes on?

    Also, can this be done by myself?








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      Check Engine - Faulty Gas Cap??? C70 1999

      Do you have over 50000 miles on that car? If it is over 50000 miles, then it is likely the front O2 sensor needs to be replaced. Our 98 S70 T5 and 97 850R went thru this same route after 50000 miles. Especially the 850R since I drive it harder on the open road.








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    Check Engine - Faulty Gas Cap??? C70 1999

    It's your O2 sensor.








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      How can you be so sure? C70 1999

      Well?
      --
      RussB in Ct '96 855T - '91 944T








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        How can you be so sure? C70 1999

        Just trust me. Go to your local dealer, and run a diagnostic for $80 or so. They will tell you the same thing, but they won't replace it based solely on someone who claims to be Mike's posted message on a msg board as such. However, the problem is the O2 sensor and not an uncommon one at that. Do tell if I am wrong.







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