Your secondary heated oxygen sensor is what triggered the fault code in your ECU. Remember that your OBD II ECU is expecting you to keep the cat, since the sensor is downstream from the cat. Luckily if the engine light doesn't bother you everything is fine. Your ECU does not make fuel management decisions based on feedback from the 2nd O2 sensor. It only makes decisions based on closed loop feedback from the primary O2 sensor, which is in the A-pipe upstream of the cat. My 2000 ITR turbo has no cat either, I just unplugged the O2 and put it in my toolbox. Eventually when my fuel tuning is done I will put a high flow cat back on the car and probably replace the secondary O2. Some older 96-98 Hondas, (which the EPA sued Honda for) the secondary O2 did not kick in the fault code at the proper voltage, so you could have conceivably run a test pipe with no engine light. In response to this action, Honda cars adhere to very strict emissions controls.