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1996 Volkswagen Jetta can not communicate with the smog check machine. Why?

My Jetta will not pass the smog test due to the readiness codes not setting. The check engine light works and is not on, and the car passes all emission tests. I have taken it to a mechanic and switched out the computer along with many other parts and still have not had any changes with the codes setting. My mechanic said to contact the state to see if there is an exception on the smog test since the problem is very strange and it is difficult to diagnose. I have 2 failed smog test reports that show the car passes everything but setting the codes. Thanks you for your time and assistance in this matter.
Answer:

We've researched information pertaining to the OBDII system of your 1996 Volkswagen Jetta. The OBD II system 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 vehicle Sound System. As odd as this may sound... 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 and further hands on diagnosis will be required. posted by SmogTips Support

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