keval9693

It’s been more than six months since I installed the short straight extenders. Don’t have any pics, but I can tell you what I used and how I did it.

First if all, I’m the founder and Monsignor of the Church of German Cars, where we pray we can fix the problem without emptying our bank accounts. Removing O2 sensors is one of those situations. Let us pray…

My Cayenne has a 4.8L Turbo engine. S and V6 engines OXS location may be different.

After putting the car on jack stands and removing bottom engine cover, the left post-Cat OXS is barely visible but touchable by hand. I put a SHORT OPEN OFFSET OXS socket (loaner from Autozone) on sensor and broke it loose using a swivel/Universal joint and 3/8” ratchet with a pipe (16” breaker bar may work.). Patience is the key as it took me awhile to figure out how to get the best leverage.

If you are so lucky to break it lose, need to unplug and unclip the OXS wire to turn sensor for removal. Having a helper from top of engine helps.

If the OXS gods are not with you, the sensor thread may be frozen and you will need heat (torch) to heat the bung first (not the OXS) before breaking it loose. I had this dubious experience trying to remove the pass (right) OXS. Had to use an alum pie tin to protect fuel lines (!) and propane torch with a flexible extension head. Fortunately the pass OXS was more accessible. I don’t think I would have been able to apply heat on the driver OXS.

May the German car gods be with you…

TRINITONY

LOL...praying helps..

So you did go from underneath, and not use a bunch of extensions from on top.

keval9693

I did look from top and bottom. The driver post-cat OXS looked more challenging to remove from the top for the 4.8L TT as it sat well behind the firewall. Perhaps you’ll have better luck/tools. Try it and let us know.

TRINITONY

If I had to do it, I'd probably just remove the HPFP if going from the top with extensions or your way proves to be too painful. I did have a P0431 popup a couple years ago right before emissions testing, and I was successful in using Cataclean. It has raised it's ugly head once since, but been off for awhile now, fingers crossed. Just preparing for if and when it becomes a nuisance.

keval9693

As a side bar, I am looking at a pressurized canister to clean fuel injectors. There is an internet video showing one can use the pressurized canister to directly clean the cat. (I used Cataclean in the tank but did not cure the problem.) If anyone has removed the pre-cat OXS, you can insert a borescope camera through the sensor bung to inspect the condition of the cat ceramic element. Assuming honeycomb element is intact (vice missing pieces), one can fill the canister with cleaner, pressurize it, and spray cleaning agent directly onto the cat element. Let soak, reinstall OXS and run engine for a few minutes. I suppose one could also use a commercially avail pressurized cleaner (make sure it's cat safe) with a long wand to spray to degrease/clean the cat element too.

TRINITONY

😆

keval9693

Upate: Since it's time for me to part with my 957 Cayennen Turbo after enjoying two years of ownership and nearly 20k miles, I can DEFINITIVELYT say the capacitors installed on the post-cat sensors signal wires prolonged/delayed the P0421/P0431 error code from triggering the CEL. The CEL stayed off for about 500 miles, which is long enough to pass my state's emissions inspection. I ended up using 470uF caps on both sides. FYI, I also cleaned the two primary cats by injecting Liqui Moly 8931 cat cleaner to the throttle body and inspected with endoscope after. There was no damage to either, and they looked pristinely clean, at least on the exhaust gas inlet surface

After cleaning, I removed the caps and installed both NEW Bosch pre and post cat oxygen sensors and 1" extenders to the post cat sensors, the P0421/P0431 pending codes would register in about 30 miles of driving, and the CEL would eventually illuminate after approx 70 miles as stored codes. (Same of before cleaning.) I reinstalled the 470 uF caps, and the CEL stayed off for about 500 miles. The P0421 and/or P0431 would be stored as pending, but they came and went on their own during the 500 miles.

All in all, I think Porsche engineers set the cat efficiency tolerance parameter way too tight, not sure if that's driven by EPA requirements. May the Porsche catalytic gods be with you all....

TRINITONY

GL - so what's the next ride?

LoBurnham

Just wanted to chime in and say that a 470uf capacitor delayed my P0431 code. I previously tried Cataclean on 2 separate occasions with no luck. My CEL would illuminate after about 50 miles of clearing the code. After installing the capacitor on the drivers side using a few T tap connectors, the CEL stayed off for about 150 miles. No wires were cut and the fix took me about 5 minutes. Much thanks to keval9693. Without this thread I wouldn't have been able to pass emissions without replacing the cat.

keval9693

Thx for the kind words and glad the 470 micro-farad cap add allowed your car to pass emissions.

To make the add factory looking and future proof, I used a 1000 microfarad (aka 1milli-farad) bipolar capacitor on the CAR-side of the post-CAT OXY sensor plug junction by inserting the two cap leads (be mindful of polarity) into the backside of each plug wire. (No T-tap or wire-splicing/cutting.) Used an ohm meter to ensure each cap lead is in good contact with each plug wire/connector. I then taped/hid the cap to the car-side plug wiring harness with high-quality (3M) black electrical tape to restore factory look. Did that for each of the two post-CAT OXY sensor junctions. This approach will allow future post-CAT OXY replacement without redoing any wiring.

Best of all, SUV drove for over 500 miles with no OXY-related CEL, probably due to the larger value caps. Cheers!