I had a check engine light the other day. Code reader has one of the catalysts was below "threshold efficiency". Quick google search said this often happens with a dirty throttle body (Jag 4.4 NA) and I had other symptoms that pointed to the TB. I had my indie clean the TB and it's running sweetly. He told me that, if that doesn't solve the problem, that the O2 sensors might have lost their proper values and that the "car would need to be reflashed". I'm not entirely sure what he meant, but he said only the JLR dealer can do it. So, can we "reflash" with the IID? If the answer is "yes", my supplementary question is, "how?"

Much thanks in advance.

Hi

It depends on the state of the O2 sensor itself:

-If its in good condition, re-flashing the Engine ECU with an improved firmware version might help. This is not supported by the IIDTool at the moment but it will be in time.
-If the O2 sensor is not working properly, re-flashing the ECU wont solve the problem. In this case, the sensor would have to be replaced and the engine adaption cleared (can be done with an IIDTool)

Cheers

To be clear - I think your mech does not have his terminology straight. When he says re-flash, he likely means clearing the adaptive values (taken from the context of what you write). 
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s
(wife thinks I'm nuts - prob right, too)

Much thanks. Info appreciated. I'll stay tuned as it looks like nice updates will be coming.