sasilverbullet

My new to me 2006 Cayman S Tiptronic with a Carnewal GT-1 exhaust is throwing P0421's every start. It's easily cleared but a real pain to have to reset it every cold start.

It only has the primary O2 sensors, the secondary ones were removed when the Carnewal exhaust went on.

Any ideas on how to troubleshoot this?

Hal

Just went to the Carnewal site to look at the products. The GT exhaust is cat-back. It should have zero impact on the converters. Do have original cats on the car?

Are the O2 sensors you do have "upstream" from the cat and another below it?

sasilverbullet

Only have one upstream from each cat. I bought a Bosch one today, will replace the bank 1 sensor and see what happens.

Hal

I did both as I guessed that if one was going bad, the other might be close behind. But I get you plan and it makes sense.

Let us know how it works out.

sasilverbullet

Fixed it, replace the upstream O2 sensor on Bank 1. Codes are all gone. Also found that there are four O2 sensors still on the car, one upstream and one downstream from the cat.

Hal

Excellent news.

From other posts I found researching this, hold off with declaring victory until you put a few hundred miles on the car.

But I suspect you are good to go.