You should inspect the 02 sensors for leaks, the exhaust manifolds for leaks or cracks, then test the 02 sensors for proper output values, and if both those things are okay, you probably need catalytic converter replacement. The ECM is measuring the differential between your front and rear 02 sensor and it doesn't like the numbers it is getting.
I don't know what your mechanic is talking about, and since I can't clarify it with him, I'd have to say he's way out in left field on this one. I mean, we should start with the obvious, not the obscure. One doesn't try to apply complicated software upgrades to what might simply be an 02 sensor failure.