Mitsu Diamante smog check, VAG-COM problem
 

Just failed the CA smog check. The emission test results are OK, but Failed during VAG-COM check. The manual scanner connected OK, no error codes. But the certified scanner (connected online) could not connected properly. Sometimes it connected successfully, sometimes not. (They tryed 2 different scanners). The problem was with reading RPM from engine. It worked properly when that people demonstrated me problem after test!!!

Mitsubishi Diamante, 1997. 160000 miles.

Do you have any suggestions?
Thank you very much.