Masked P0420 with COBB AP. Now P0037 surfaces.
 

Recently obtained a Cobb AP V2. Using an old MazSport DR MP and have a CEL. Went through the process of marrying AP, using ATR to unchecked P0420 in Advance Parameters -> DTCs, and flashing that stock map onto the RX-8. There was no CEL after the flash.

Today I checked if it is ready with my OBDII scanner using Torque (expected unready due to lack of drive cycle) and right away, I see a CEL. I scanned it and it came up to be "P0037 Rear HO2S heater control circuit low ON 2 HO2S heater." The Catalyst, Evap Sys, Secondary Air Sys, and O2 sensor is still listed as "INCOMPLETE/NOT READY".

Could I need a new rear O2 sensor? If so, is it possible to mask the P0037 with Cobb AP and still have no more than one DTC unready? NYS Inspection is due and requires no more than one unready with zero DTC's (CEL). Just need something for the interim so I can get the inspection done ASAP.

I don't think you'll be able to pass. The P0037 means your rear o2 is done, and without rear o2 you will never get a ready check on cat/o2/air injection. But the rear o2 sensor is relatively cheap and with a working sensor you should be able to mask and pass. hope that helps.

With a low circuit P0037 wouldn't that mean there is a break in the circuit?

I checked the connector and cables, which are seemingly fine. Might grab a universal Bosch o2 Sensor and solder it into the original connector.

It generally means the o2 sensor heater is broken. A universal can work, but I've heard they don't last long with rotary engine heat. Never tried it myself, but I'd say it's worth a shot.

Could also pick up a used one off fleabay or the forum.