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on Rs4 do these effect anything.
Tried to log them on ob2 but got 0.00v readings on both, could this be my issue being down 30hp?

Thanks G

What these post cat sensors do is make sure the cats are doing their job. The generated voltage will be stable if the system is working correctly.

The Pre cat sensors should fluctuate the voltage quickly allowing the engine ecu to trim the mixture based on what they sense. If its slow, they may be aged or clogged. this will reduce the effectiveness of the engine to produce max power.

Morpheous, in what blocks do you read the post-cat lambda sensors on a 8D0 907 551F RS4 ECU? Does this specific ECU actually check for precats existance or not? Curious to see what you think vs reality.

Just trying to help, Obd2 allows you to log all but this is on my ecu cant speak for Morpheus.

Nearly gone out the door to , you know where. Need a fix quick.

Quite true I know close to nothing but "trying" all the time

Dont know what version this chap drives, could have been a new RS4 for all I know, this is a general reply for others who are interested in what these do.
Are you telling me they are fitted to the car cos it looks good? or does the ECU actually use the info.
Might want to try winding your neck in.

Now now people

Blimey whats this then?

Anyone would like test info or wiring diag PM with DATA sticker and email... ER S2T dont bother

Morpheous, in what blocks do you read the post-cat lambda sensors on a 8D0 907 551F RS4 ECU? Does this specific ECU actually check for precats existance or not? Curious to see what you think vs reality.

What are you talking about, it cant check for the existence of the pre cat.

I obviously need to clear this as you are confused.

Forget testing of pre cat itself this is what I was trying to say:-

You have bank 1 or 2 probe 1 which is the pre catalytic converter probe which does most of the sensing work B4 the gas is cleaned by passing through a catalytic converter.
Bank 1 or 2 probe 2 is the probe after the catalytic converter which checks for correct operation of the cat by sampling the cleaned exhaust gas, if the cat is knackered, this probe would detect the cat is not doing its job. If this is the case, catalytic converter low efficiency is flagged up.
It does not check to see if someone has removed the pre cat.

Morpheous, what I'm talking about is the fact that an RS4 551F ECU coded to 04711 doesn't give a damn about the secondary lambda probes and it doesn't care of the precat existing or not. Nor does it display the secondary lambda output voltage. This is something that ELSAWin doesn't tell you, but be my guest and connect to such an RS4 and you'll see for yourself (block 031).

Don't get my posts as arrogant but only as a way of testing you...

Mihnea

oh, by the way, have a look at the RS4 exhaust system and you'll see that the secondary (B1/2S2) lambda probes only check for the precats, not the main cats. They are mounted right at the inlet of the main cats.

And, on a 551F ECU, the codeword DKAT (catalyst diagnostics) is set to 0.

now if you still think I'm arrogant, fair enough, I'll leave you to it!

Mihnea

Well I dont have time for playing games, sorry. I try to help as much as I can.
I don't know as much as Dippy etc which is why I try not to post for tuned stuff.
Yes my Y reg S4 was chipped by Kim but thats now long gone, this is why I only check in now and then.
Again, I only post if I'm sure I can point someone in the general direction to help them.
The MVB is 37/38 for ASJ engine. Not sure what the ECU no is.
Here is the code table for 04711

04 Emission standard EUII
7 4WD with traction control / ESP
1 6 SP manual gearbox
1 Audi A/S 4

oh, by the way, have a look at the RS4 exhaust system and you'll see that the secondary (B1/2S2) lambda probes only check for the precats, not the main cats. They are mounted right at the inlet of the main cats.

Yep you are right, looks the same as S4 looking at elsa.
Don't see these much any more and getting old hence the memory loss. On the new stuff its different and as stated.

Now that was superb display of knowledge, well done. I am very grateful for the help you all have provided.
Morpheus ,The research quality you provided to support your points was exemplary. Thanks to you both for the education I'm still confused but I do understand much better how these dont work and its not the first time Mihnea has old me this, Thanks again guy and all people helping on the site. So sorry to have these problems with my car. I will share the cause when I find it. Kind Regards G