i have a 2002 yukon xl denali with a 6.0. i am running a whipple 2300ax at 6psi. the truck performs well, but im getting a P0240 dtc.

it says bank1 catylitic converter system operating below threshold.
what the hell does that mean? i have a jba cat back stainless exhaust, thats the only other mod to the truck.

Blu, Did you fix it by now? Here are causes I found:

-Leaded fuel was used where unleaded was called for
-An oxygen sensor is not reading (functioning) properly
-The engine coolant temperature sensor is not working properly
-Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
-Retarded spark timing
-The oxygen sensors in front and behind the converter are reporting too similar of readings