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    Check engine light

    came on about 2 days ago but the car still ran like a sewing machine. I didn't have to time go by a auto parts store to let them hook it up to a machine. Now the light is off & hasn't come back on. Should I still run by & let them check it to see if any codes pop up?
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    2000 Protege ES

    #2
    I would still scan it. A code could still be stored in the computer even if there's no problem anymore. My check engine light never came on when my car was constantly stalling, but I scanned it anyway. Turned out to have a cylinder one misfire code, just never turned the light on. Scan it anyway, just to be safe. It's usually free and takes maybe 10 minutes.

    Sent from my HTC Incredible using Tapatalk.

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      #3
      I'm hoping it's something like a gas cap & not an eletrical problem I'm not so worried about it being a cat we don't have state inspection here.
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      2000 Protege ES

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        #4
        I don't think the light would turn off if it was a cat, though.

        Sent from my HTC Incredible using Tapatalk.

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          #5
          A bad cat doesn't trigger the CEL, the O2 sensors do. The post-cat sensor is the one that monitors everything going on in the cat. Odds are you have an O2 sensor code, maybe something in the evap system, or a misfire. Since the light went back off, and you didn't notice any problems while driving it, odds are your gas cap was loose, or something else minor like that in the evap system.
          1995 626: daily beater, mostly stock. Future NASA racer?

          Next up: Speed6 or RX-8

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            #6
            The purpose of the second O2 sensor is to monitor catalyst performance. If the values detected by that O2 sensor are out of a certain range then you'll throw a code because OBDII vehicles must monitor catalyst performance.

            Here's a graph I made when I had my Passport. The left shows the upstream sensors, the right the downstream sensors. This was a V6 with two cats (one on each bank and had an O2 sensor before and after each cat).

            When you have no cat or a bad cat then the right side will almost mirror the left 100%. It's this 100% match that throws the code.

            As you can see the right bank cat (lower graphs) is more efficient than the left bank (upper graphs) since the right cat's secondary O2 sensor approaches more of a straight line. In any regard you see the peaks and valleys of the upstream sensors...this is what you want.



            If you graph a Protege it would show one upstream and one downstream sensor. If the downstream sensor's values match the upstream sensor's on a nearly 1:1 basis then you get a code telling you the cat is bad. It could come and go if there are exhaust leaks, etc.

            Neither a downstream O2 sensor code nor an evap code will affect performance, so, you engine will perform as normal when these codes are thrown.

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              #7
              I looked it up in the manual & it said

              1. Gas cap is loose or needs to be replaced

              2. Wiring problem

              3. A ROOM fuse is blowen

              4. The gas tank is almost empty.

              5. The emission control is having issues

              I am HOPING it's either 5 or 3

              Taking it to the auto parts store tomorrow great way to spend my one day off a week!
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              2000 Protege ES

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