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cavalier cannot be inspected, cant connect to obd2port,possible problems? Please help

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  • cavalier cannot be inspected, cant connect to obd2port,possible problems? Please help

    Im looking to buy a 2001 cavalier. If you hook up a obd2 scanner to it it wont connect. The mechanic said the main computer and the compuvalve arent working. Would the bad compuvalve make it so you cant get a reading or connection? Is the main computer in this car the same as other cavaliers or is it made just for bifuel cars? Also i heard you can take the compuvalve apart and fix it. Is this true? Anyone know the cost of these parts new or used? Any help would be gladly appreciated. The car runs and drives fine on unleaded gas. I was told the cng tank is empty. It doesn't have any check engine lights on. Thank you

  • #2
    Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

    If OBD2 won't connect, that's a whole problem in itself. If it were working, my understanding is that OBD2 won't tell you much about the CNG system. I would try putting some CNG in the tank and see if it starts on CNG or if the fuel gauge switches back and forth when you push the button.
    02 GX
    01 GX
    03 Crown Vic
    06 GX
    Home Fueler

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    • #3
      Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

      The Cavalier does not have a "compuvalve". It uses a totally different system then the earlier cars or the Ford vehicles. A 2001 AF ECU will output OBD codes, however the car must have CNG in it and must be running or able to run on CNG (red light out) before they can be read. To switch between fuels, the gasoline ECU power is shut off and power is applied to the natural gas ECU. On the '01, the gasoline ECU is located on the inside of the right front wheelwheel and the natural gas ECU is located behind the left headlight. There are too many other things that could be wrong that it would be unwise to buy a bi-fuel car without getting it to run on CNG or somehow obligate the seller to refund your money or make repairs if after the purchase there are problems.

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      • #4
        Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

        So your saying the ecu for the gas and the one for the cng could be bad? If so i would imagine the cng one is very expensive and hard to find. Any other thoughts?

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        • #5
          Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

          Another question. If i cant make a connection to the port to get a reading or to pass inspection it possibley could be it just needs cng in the system to work to get a code?

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          • #6
            Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

            mjmirra...

            So you're saying when a OBD reader is hooked to the car it tells you the OBD is not ready? or what exactly is happening?


            When I first bought my cavvy I had a problem because they could not do emissions because the OBD was not ready. my mechanic buddy reset the computer and cleared all codes. I then had to drive the vehicle for a total of anywhere from 50-200 miles so the vehicle can go through all it's own diagnostics to get the OBD ready for testing. This is part of the normal cycle for the OBD's.

            I could only get a readiness that was 6 out of 7 which for my cavvy (2000) was good enough to pass for that model year. However that being said, my mechanic also told me that the fuel gage in both tanks need to register around 3/8 to 3/4" full ... no more and no less ... The OBD performs it's full checks when the tanks are registering these levels (this has to do with the EVAP system and such as I understand it.).


            Hope this is of some use.

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            • #7
              Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

              Cant even get a reading at all. Its like the port is dead. Checked for a bad fuse and thats ok.

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              • #8
                Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

                If the fuse is good and you cannot get a scantool to connect at all but the car runs with no check engine lights, the first thought would be a wiring issue. It sounds like you are located where it is difficult to fuel the car with CNG. Fueling with CNG would answer the most important question to me---will it run on CNG before I buy it. The OBD issue can be addressed later. Two questions--do you remember seeing the little red light located on the "fuel" switch illuminated? This would indicate that power was being applied to the CNG ECU and that the fuel pump relay was operating. Second, when you turn on the key does the check engine light go on for a couple of seconds during the bulb check?

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                • #9
                  Re: cavalier cannot be inspected, cant connect to obd2port,possible problems? Please

                  Not sure about those questions you asked me. I will have to find out and get back to you. We have a couple of local cng fueling stations here. Would love to have a home fueling station but i cant see spending the money for it unless i have a fleet of cng vehicles, haha Thanks to everyone for your help so far.

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