Computer problem
1997 BMW 328 6 cyl Two Wheel Drive Automatic 150000 miles
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Requested a smog test since i plan on putting my car up for sale. It passed the part of the test involving the tailpipe, but independent mechanic couldn't get his smog machine to communicate with car's computer. Took it to bmw dealer and they say i have to pay for 3 hours labor for diagnostices ($420), not including cost of repair whatever that might be. Are these my only options.
Help

No, I have seen this happen many times. When the underhood diagnostic connector does not have the cap on it there is no communication to the OBDII connector. Replace the cap on the diagnostic connector and it will start to communicate with the generic aspect of the smog machine.