Hal

Last August, a few days after my state annual inspection, my 2006 Cayman S threw a CEL. Car was running fine so I continued with my errands. Got home, and pulled out my Foxwell 530 with Porsche software.

P2196: O2 sensor stuck/biased Rich Bank 1 Sensor 1
P0421: Warmup catalyst efficiency below threshold Bank 1

I spent a great deal of time researching this before attempting a fix. It seems this is a common, but not frequent issue. It looked to me that the cat code was a false positive and caused by the bad O2 sensor code. The fixes ranged from adding O2 spacers, to new O2 sensors, to new cats.

Researching replacement cats, it all depends on the level of expense you are willing to tolerate. As of today, a new, single cat from Porsche is about $2,000 and requires returning the old one as a core. Used ones are out there and prices vary among vendors. Aftermarket cats are available but you have to decide between EPA compliance and performance. If you have the time and patience, Carnewal has a great rebuild program. Soul has a great set of performance cats, but expensive. I was ready to go with Magnaflow as they were 47 state EPA compliant and very attractively priced. Fortunately, I did not need to go that route.

I discussed my codes with one of Rennlist's sponsors, Soul Performance. He though spacers were a good place to start and he suggested the JCarPart O2 Oxygen Sensor Spacer. I bought a set and had my mechanic install them. On his test drive he said the car ran terrible and removed them.

They then ordered in Bosch O2 sensors (upstream only). I insisted on Bosch as Porsche branded sensors were ridiculously expensive and I had seen posts where the cheap ones failed to even function.

These were the solution to my problem. I have several hundred miles on the car since and candidly, the car has never run better.

Hope this helps anyone searching on these error codes in the future.