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Hello Experts,

I have a 2013 cayenne diesel in India and due to the relatively lax emission norms here the car came from the factory without the DPF.

I have now added a decat downpipe and the car revvs relatively freely compare to with the cat. The original downpipe has a precat 02 sensor and post cat temp sensor and these have been integrated into the decat downpipe as well.

However after adding the decat downpipe I get a P0721 error, this is related to the Output shaft speed sensor. When this error is preset it results in jerky engagement of Drive and Reverse, especially when starting on a slope. This error goes away when I put the original downpipe with cat back on.

Can someone please explain if/how this error is related to the decat donwpipe? Would getting a stage 2 tune take care of this error and associated transmission issue?
 

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First of all that P* OBD Code is generic and dont mean diddly squat, you needa scan it with a VAG specific diagnostic tool to gealm any real insight..

The code has likely related to the ECU detecting the operating parameters are out of spec, a tune should fix that as it would change the spec.. if its building more boost sooner than it expects and whatnot will cause a fault in a stock ECU.
 

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Interesting to hear that the engine seems to breathe more freely with just the downpipe change.. To be clear - you did the downpipe just because you wanted to, correct? (Not because there were other issues?)
I've been debating on adding that to my car, but hadn't read anyone's experience who already were DPF-less and then added the downpipe. Most seemed to do both at the same time as a tune. (y)
 
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