I have a 2000 Altima GXE that has failed the smog test for NOx. I also have a problem with the OBD not responding to some of the items. I have been getting the runaround in terms of how to fix this. The repair manager at a local Nissan says it's probably the wiring and they can check it out with a simple diagnostic. Now the mechanic there is driving it around trying to trip the OBD to get a reading and they're saying I will probably have to replace the ECM. I've also been told I have to replace the catalytic converter. We're looking at over $2k here for a used car. Any suggestions or recommendations will be welcome. I had this problem 2 years ago and they replaced the intake manifold gasket for over $600, and I had the same OBD problem.