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1999 VW Jetta GLS not communicating with the smog check machine, why?

My Volkswagon Jetta is not communicating with the smog computer and 3 mechanics can not figure out why. I'm in the process of selling the car and the car is running fine.
Answer:

Do you have a radio installed in your Jetta other then the factory stereo? I have researched information pertaining to the OBDII system of your VW Jetta GLS which is responsible for the communication between the smog machine and your vehicle's Engine Control Unit. It is possible your vehicle has a model of the OBD II Engine Control System which is connected to your car's sound system. If the original radio in your vehicle has been replaced, this may cause a problem with the smog inspection. There are simply two solutions to this problem. First you may see the vehicle's dealer/manufacturer and explain your problem. They may be able to re-program your engine computer to function with the new smog equipment. Your second option is to have your vehicle inspected by the State Referee's Office. They may bypass the smog equipments OBDII connection system and PASS your vehicle. You may reach the Referee's Office at (800)622-7733. If the radio in your vehicle is the original, it is possible there is an OBDII problem unrelated to the sound system. Finding the reason why there is a communication error between the smog machine and your Jetta's engine control computer or OBD II system will require hands-on diagnosis. If the mechanics you've spoken to can not figure out the probable you may need the dealership to inspect this fault. posted by SmogTips Support

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