Tools needed: a set of assorted wrenches and sockets, breaker bars, 22mm o2 sensor wrench, aerokroil or pb blaster for loosening bolts, several wrench extensions for the down pipe, "j" hook type tool, 1/2" drill bit and a drill, set of non foulers, vagcom laptop setup
Time anticipated : from 2-4hrs depending on how much is taken apart
Difficulty : maybe a 5 its again just a basic unbolt and bolt back on for the test pipe. the 02 sensor non fouler mods to keep a CEL from coming on might take a lot of patience to figure out
lets get started :
Make sure that your car is cold so you don't burn yourself big time on the hot cat and the engine. Its also a good idea to start vagcom and do a full scan noticing and clearing all the previously saved codes in the ECU.
Jack your car up as high as you safely can to allow maximum workspace underneath.
Spray some aerokroil on the turbo to cat bolts x3 and the cat to down pipe bolts x3. Also spray some onto the sleeve between down pipe and the rear section of the exhaust to allow easy removal.
In order to remove the catalytic converter you will have to disconnect the o2 sensor from its connections and unscrew it from the pipe. Both 02 sensor connections are on the firewall just underneath to the L of the coolant expansion tank near the famous L hose. The black connector is the front o2 sensor and the brown one is for the rear.
Those connectors are clipped into the firewall holders, twist them slight and they will come out. I didn't disconnect the front o2 sensor from the connector but you could do that so you don't twist the cable to much when unscrewing the front o2 sensor. The rear 02 sensor connection is best to be disconnected as it is very hard to unscrew the rear one from the cat when installed in the car.
Disconnect the brown connector from its wiring.
The wire might be tied to some other wires and is routed behind the engine, break those ties to allow the wire to become loose for later.
Start taking the air box out to allow even more space for working on the upper levels of the car, remove the snorkel that's clipped into the top of the air box, also slightly twist and pull up on the rubber seal on top of the air box for the MAF. In case you have an older car you will have to disconnect all the ignition amp cables as well.
After you have pulled the rubber plug away you will have approx 1" or so of cable slack. BE VERY CAREFUL TO NOT BREAK THE MAF WIRING! Now comes the J hook into place to remove the MAF cable from the MAF itself. It's a connector just like on the windshield washer sensor. You need to pull the clip slightly away from a ridge in order for it to come loose.
The picture is slight blurred and over exposed, sorry. But hopefully you get the idea. After the cable is disconnected unscrew the big rubber hose, the small plastic one for the 2nd air injection pump and unclip the metal line from the air box lid. You should now be able to lift out the air box lid out of the car. You could now stop here or keep going and remove the whole air box for even more space to work. The box is held on with a 9mm bolt on the fender and pushed into rubber plugs on the frame, lift it straight out.
The car should look like this now with the box removed.
Take either a 02 sensor wrench or a 22mm wrench to remove the front 02 sensor. That thing might be VERY tight so be aware, its also a good idea to use anti seize upon reinstalling. Unscrew the front sensor and stash it out of the way.
If you have a lot of miles on the car and just short or 100k miles it might be a good idea to replace the front sensor anyways if you are already that far to keep it from causing issues later on.
Now remove the 3 turbo to cat bolts, those are 17mm ones and will be very tight. Loosen them up all the way and get underneath the car.
To make the down pipe to cat bolt removal a lot easier its best to loosen up the rear section as much as you can, if you have an exhaust that can be disconnected just after the flex pipe do that. Also disconnect the spring tensioned bolt that is attached to the down pipe. Doing this step will make life a whole lot easier on you.
Also in case you want to try to remove the cat and down pipe in one piece: it won't work! Believe me I've tried for one hour before giving up.
The down pipe has three 13mm bolts that are attached and have to be loosened up. Those are a pain if everything is tight and not moving. Since the turbo and cat are loose and you also loosened the bottom down pipe connections those bolts could be a pain but you can move the down pipe and cat around slightly and gain better access to those bolts. Unscrew the bolts and take down pipe out through the bottom of the car.
The cat will slight down after the test pipe is removed. Pull the cat out making sure that the rear o2 sensor cable doesn't get tangled up anywhere. Remove the rear o2 sensor from the cat and enjoy that you have just done some work that most people give up on.
No cat and down pipe
Cat and down pipe together
Cat and test pipe next to each
In case you are planning on replacing the cat with a test pipe on your DEDICATED TRACK CAR you would have to use so called spark plug non foulers.
Those non foulers are needed on our cars have a thread size of 18mm and come in two different sizes one is long and one is short.
The company that makes them is HELP and those are available at your local car parts store.
42009: SHORT non fouler 2 per pack with 2 gaskets
42002: LONG non fouler 2 per pack
Here is where it gets confusing and different for the different engines in the B5 A4.
Some cars get away with a non fouler that is drilled out to accommodate the 02 sensor while others don't need to drill the foulers out at all.
The most commonly found description of running non foulers is to use a short non fouler that is drilled out on top of another regular non fouler into the pipe.
So it would be 02 Sensor| drilled short fouler| non drilled short fouler| test pipe.
Here is a poll done that shows how people stack the non foulers on different engines to avoid a CEL
It will basically a trial and error with the test pipe and non foulers on ATW engines.
More on that later at the end of this.
In order to drill out non foulers you will need a 1/2 drill bit or even better a 19/32nd. Pay attention though to how you trill, if you are no centered onto the fouler you will collapse the outside threads real easy. A drill press works great for this job but you could also just drill the fouler while it's in the test pipe and then clean your metal shaving mess up.
Back to the test pipe; if ordered from ecode it comes only with a down pipe to test pipe gasket and not a test pipe to turbo gasket. Make sure you either have a new turbo to test pipe gasket or just reuse the old one at your risk.
Get your combination of non foulers ready and screw them into the test pipe using antiseize on the threads; also take your old rear 02 sensor and screw that one into the nonfoulers which are installed already into the test pipe.
Install your test pipe |replacement cat back into the car using the steps above that you have used to remove the thing in the 1st place.
Connect all the wiring and put everything back together. Don't worry to much about the rear 02 sensor and it's fouler at this time. With the test pipe installed you can easily change the sensor within 10 minutes without removing anything at all. It's very easy to get to.
If everything is back and place and looking like above use your vagcom and clear any codes that might have came on during the install. Make sure that the 02 sensor cables are connected.
This is my old logging sheet with the NonFoulers on the ATW Engine. Kept getting CEL's until the block was installed.
17526 - Oxygen (Lambda) Sensor Heating; B1 S2: Open Circuit
P1118 - 35-00 - -
17522 - Oxygen (Lambda) Sensor; B1 S2: Internal Resistance too High
P1114 - 35-00 - -
Were the codes that I had and also the following code after a period of idle
16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
P0140 - 35-10 - - - Intermittent
these codes came from the old audi 02 sensor that somehow got damaged during the testpipe install
I remembered people talking about a VW 02 sensor that is very cheap 24$ to be exact to work on the ATW engine. It will only work on the front pre cat position and is a direct plug in from the factory.
The sensor is that cheap because its part of a recall action from VW on some dubs so its 30$ of the shelf or 24$ online. Part number 06A-906-262-Q
The sensor itself is just like every other 02 sensor that I had seen on the ATW its a 4 wire sensor. The VW one had the same tips, size, threading, weight, height etc as the Audi one except a different part number and a VERY long cable on it.
So I decided to give it a try to run the VW sensor in the rear since it's physically the same i looked at the plug. The Audi sensor is the brown plug and the VW is black. The pin layout was the same as well, the only difference is that the brown connector doesn't have a "squared" corner like the black one has, otherwise they would be exactly the same. The corner I am talking about is in ten TOP LEFT of each connector.
The next pics are slightly blurry. SORRY
VW connector versus audi connector on the car.
after taking a file and filing down the corner to make it round as on the brown one it fits right into the firewall connection.
The VW is sensor installed and the slack of the cable laid over the battery temporarily.
Audi sensor on the right and the VW sensors cable length on the left.
After swapping the VW sensor into the car and not getting the old codes that I had before i figured out that my old 02 sensor must have been somehow damaged after my ordeal with the testpipe installation.
When I did research it seemed that nearly all AEB engine could be fooled with the non foulers for the rear o2 sensor. Some AWM engine seemed to save codes. NONE of the ATW engines made it without a CEL or CODE so far during some point and time.
AEB and AWM Engines
Block Writeup is HERE