[dmenn]

Here is the description of the codes from the Durametric Tool:

P0133 - Porsche fault code 15 - sensor ageing behind cat (conv. cylinder (1-3) below limit value)

P0153 - Porsche fault code 21 - sensor ageing behind cat (conv. cylinder (4-6) below limit value)

This is saying that the voltage on your post-cat O2 sensors is too low. Are they in the stream of exhaust gas? I know when I initially put headers on I just tied up the sensors in the engine area and didn't put them in the exhaust flow. I got both of these codes because the O2 sensor wasn't reading any exhausts gases. The engine computer was smarter than I thought.

If the catalytic converter is doing its job, the voltage should read a lower voltage than the pre-cat O2 sensors. You'll see major flucuation in the pre-cat O2 sensors from between .1 to .8 volts. I haven't driven the car much since putting my post-cat O2 sensors in on the car and extending the O2 wires, so I can't comment on the voltage yet for my post-cat O2 sensors and if any CEL will go off. So far though, nothing yet.