I had my 2011 GSR tuned ~3 years ago.

I went to a local tuner who was well-recommended. I let them know my exhaust was throwing a P420 code from time to time and asked if they could prevent that.

Shortly after the car was tuned, I needed to get it inspected and found that the downstream o2 sensor was never going to the ready state, and that included the heater element. 2 sensors is a fail, so I took the car back to the tuner and let them know. They worked on the car a bit more and sent me on my way. I was able to get the inspection completed.

Fast forward a year and I when I went to get the car inspected again, it failed for the same reason as previous - downstream o2 and heater element not ready. I went back to my original tuner and they are no longer with the company and not doing any tuning.

I contacted the only other tuner in my town and they are backlogged to the point that they couldn't take in my vehicle. They recommended I get on the forums and see if anyone could help. Their guess is the sensor or circuit was "defeated" by the original tuner and needs to be reverted.

Thats about where I am now. Ive been trying to get the sensor fixed for about 2 years now and Im running out of ideas. Any help would be appreciated.

 

Your rear o2 was turned off in your tune. Mine was the same way, and I simply "forced pass" the monitors in the rom to find an even better solution. I had an Evo 9 (now sold) though- so my software and rom setup was different. You should just use the "o2 sensor spacer" trick to get by the catalyst check as long as the catalyst verification strategy is a simple index switching ratio check (like many cars had for years)

Some newer cars use oxygen storage checks in the catalyst- so the spacer trick does not work.

 

Yes, I previously used o2 sensor spacers to help pass inspection. I will likely re-install those if I can figure out how to get the sensor turned back on.

If anyone is able to help out with that, I would appreciate it.

 

Research on how to re-enable your rear o2... or see if there is a way to force readyness