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2000 Cavalier CNG AF ECU Information

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  • 2000 Cavalier CNG AF ECU Information

    I need to replace the Alternative Fuel Engine Control Unit (AF ECU) in my 2000 Cavalier. I checked with the Dealer and the part will cost at least $1500. While I would like to get this car back on the road ASAP, this price seems very high.

    Answers to any of the following questions, would be helpful:
    Can the AF ECU be rebuilt?
    Are used ones available?
    Will all Cavalier AF ECUs work in my car?

    I look forward to hearing from other people that have experienced this same problem and especially from the ones that have found a solution.

    Thanks in advance!

  • #2
    Re: 2000 Cavalier CNG AF ECU Information

    1999 through 2001 AF ECU's will work in your car. Most pickup and van ECU's will also work except they need to be "reflashed" with the proper code to run a Cavalier. Diagnosis and repair of the board is unlikely--there are "no user servicable parts" inside. The big problem with the AF ECU is corrosion that gets in from failure of the gasket between the housing and the cover. I have gone over this before on this site. You could try taking it apart and cleaning the board and connector area to see if it will bring it back to life. I fixed at least one by cleaning it and removing the aluminum oxide residue from around the connector area. Are you sure the problem is the AF ECU and not the GMS/MCV? A couple of hundred bucks usually gets you the ECU when they come available on E-bay or Craig's list.

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    • #3
      Re: 2000 Cavalier CNG AF ECU Information

      Anyone know why my AFECU is dead above ~40F?

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      • #4
        Re: 2000 Cavalier CNG AF ECU Information

        Can you direct me to your discussion about the following:
        "AF ECU is corrosion that gets in from failure of the gasket between the housing and the cover"

        I am having a problem getting the bolts loose on the AF ECU cover. Also, interested in what you used to removing the aluminum oxide residue.

        Thanks,

        Jerry

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        • #5
          Re: 2000 Cavalier CNG AF ECU Information

          It's all somewhere in a thread but I couldn't find it in my old posts. Basically you need to soak the screw heads in penetrating oil and remove as many as you can. The ones that won't come out (in my case) were removed by cutting a slot in the head with a dremel tool and then using a large common screwdriver tip in a impact gun. If that fails, just grind the head flush with the housing and as long as there aren't too many of them don't worry about replacing them. When you get the cover off, lift the PC board out of the case. Be careful as the board is glued to the case around some heat sinks in the back--a gentle pull will get it loose. The board is conformal coated so getting it wet won't hurt anything. Clean it with soap and water and make sure you clean well around the connectors at the bottom of the board and dry it all with compressed air. When dry, I would connect the board to the plugs on the car and see if it will run. If all goes well, clean up the case and cover with a sanding disc on a dremel tool. Don't worry about the "O" ring its groove. Throw the "O" ring out. When re-assembling, fill the "O" ring groove and glue the case and cover together with something like "Yamabond". This is an adhesive sealer used to seal cases of motorcycle engines together and available at any Yamaha dealer. Put as many screws back in as you can--they are metric but can be bought at any decent hardware store. I used stainless with antisieze compound on them but hopefully I will never have to take the ECU apart again.

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          • #6
            Re: 2000 Cavalier CNG AF ECU Information

            I was able to get the case apart, clean the board with dishwashing soap and then give it a good rinse. I noticed that there was a small amount of corrosion where there was a break in the conformal (rubber) coating. I gently scrapped off the corrosion and then blew the board off with compressed air. Fortunately, when I connected it up on the car, it still worked.

            Should I use any additional work to clean off the corrosion on the board?

            Is there something that I should use to seal the place where the conformal coating is missing?

            Thanks in advance!

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            • #7
              Re: 2000 Cavalier CNG AF ECU Information

              If you found "Yamabond" to seal the case, use it to coat the spot where the conformal coating is missing. Otherwise just about any kind of resin can be used by just brushing it on. Make sure you use a corrosion preventitive like "Corrosion Block". "Corrosion X" or "Boeshield T-9" on the connectors before reinstalling them.

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              • #8
                Re: 2000 Cavalier CNG AF ECU Information

                I do have a couple more questions:

                Should I use Yamabond #4 (Grey and pliable) or Yamabond #5 (Black and hard)?

                The corrosion is white and looks more like what I would see around a battery terminal. It certainly does not look like rust. Should I wash the parts with baking soda to neutralize any acid?

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                • #9
                  Re: 2000 Cavalier CNG AF ECU Information

                  Clean the area the best you can and spray a corrosion preventitive on the area and just leave it there. The Yamabond is the #4 grey that you are looking for---excellent product

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                  • #10
                    Re: 2000 Cavalier CNG AF ECU Information

                    siai47,

                    I just finished assembling my Cavalier and taking it on a test drive. It is running great on CNG!!!
                    In addition to disassembling and cleaning the AF ECU, I had to replace one of the pins on the pigtail that connected to the AF ECU. I think that this was actually the problem. I was able to get an individual replacement pin from my local Chevrolet dealer. It cost $3.00 and was relatively easy to replace.

                    Thanks for all of your help!

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                    • #11
                      Re: 2000 Cavalier CNG AF ECU Information

                      I just saw a 2002 CNG Cavailer on ebay. From the pictures the CNG system looks identical to my 2000 CNG cavalier. You mentioned that the CNG components were the same for the 1999-2001. What components are different on the 2002 and beyond?

                      Thanks,

                      Jerry

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                      • #12
                        Re: 2000 Cavalier CNG AF ECU Information

                        The 2002 Cavalier has a different type of ECM (engine control module) which is mounted to the passenger side shock tower whereas the earlier models have the ECM mounted in the passenger side forward frame area ahead of the right front wheel. This change involves wiring harnesses and AF ECM programming changes. Other then that, the rest of the system is identical. With the execption of the fuel select switch, the 2003 and beyond systems are totally different (nothing interchanges) from the HPR forward.

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                        • #13
                          Re: 2000 Cavalier CNG AF ECU Information

                          Would I be able to actually use the AF ECM from a 2000 CNG Cavalier and put it into a 2002 Cavalier if a Chevrolet garage would re-program it for me or is it a completely different unit?

                          Also, is the 2002 Cavalier AF ECM still located ahead of the driver's front tire?

                          Lastly, are there any improvements with the 2003+ CNG systems over the 2002 and previous models (Better mileage, more reliable, starts better on CNG, etc)?
                          Last edited by jerryryan; 07-17-2011, 11:43 PM.

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                          • #14
                            Re: 2000 Cavalier CNG AF ECU Information

                            Yes you could use the AF ECU from a 2000 in a 2002. The ECU would need to be installed into the car and then it would need to be taken to the dealer to "re-flash" it with the proper program. I am not sure if it would run with the 2000 program installed but it would be worth a try. If it doesn't work, just pull the CNG fuse until you can get it reprogrammed. As to the 2003+ cars, they are a vast improvement over the older cars however nothing is common between them on the engine side of the system as the newer cars are fuel injected and use a different engine. They have more power, start and drive at all times like a normal gasoline car and get better fuel economy. If you really like CNG and can score a 2003+ Cavalier--then by all means do what it takes to get one.

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                            • #15
                              Re: 2000 Cavalier CNG AF ECU Information

                              Is the ECM in the CNG Cavaliers the same as the ECM in the non-CNG Cavaliers?

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