WOT Fault Resolved

[blu_s2]

For those who remeber my WOT fault.... with the help of Paul N and schematics it was resolved yesterday...

Bottom line... caused by a faulty (but only just) baromtertric pressure sender.

The ECU uses a combination of resistance from the throtlle pot and the pressure sensor (which is located behind the UK passenger kick plate) to sense WOT.

After a couple of hours testing with multimeter and breakout box and the usual "mmmmmmm, sounds plausible, but why on earth did they do it like that" S2 logic we swapped the sensor from Paul's car with mine and hey presto overboost through WOT.

Paul will post the resitance values of my duff sensor versus his for anyone (Peter?) suffering similar problems, as well as the Audi and Bosch Part numbers.

If anyone is wondering with the sesnor disconnected the ECU defaults to a set value of 968millibar of atomspheric pressure and the car looks as though it uses overboost cutout protection to prevent excess boost.

The sensor is approx £40+vat from Bosch.

As you can imagine I'm seriusly glad to have it back to 'normal'.

[Pete_RS2]

Glad you finally got it sorted Jim Yes mine's got a similar fault. Don't suppose you can post any pics of that sensor location ? Mine's got the dealer fit air con so things have been moved around in that area.

Have fun with the overboost Wooosh!

[blu_s2]

Sensor....

[blu_s2]

Location... the sensor is held in place by a single screw behind the (blue) metal panel, follow the yellow taped wires

[Beetie]

Ah, so yours was the one my ecu might have been tested on if i managed to get it back in time?!
Mine keeps coming up with an internal ecu fault, but when i get it back i will get it chipped aswell....
Paul, would it be better if i bring the car to you, or just send the ecu to you with the fault stored (should the fault be stored when disconnected?)

[S2central.net]

@Peter with his S2 Avant that never sees WOT - and anyone else with the inclination and a multimeter. Here is how to test the altitude sensor (F96) on your S2 - 3B or ABY its all the same.

The location of F96 is on the passenger side - at the bottom of the A-pillar - just behind the trim panel which removes with one cross-head screw. You need to carefully tease back the door seal to move the trim away. You will see the moisture trap for the control line to your ECU, but ignore that !

Then you'll see a wadge of clear tape which covers the hole in the A-pillar where F96 lives. Think Jim posted pix already... Tease that back and carefully remove the one locating screw (cross-head) that secures F96 to the body. Be careful not to drop the screw - only a childs fingers could release the connector without removing F96 from this location. The part number is 853 919 562 or 0-280-101-001 in Bosch lingo.

When its out of the A-pillar, remove the connector to separate the device from the loom, and note the pin nomenclature 1-2-3 on the device. With a DVM set to below 5kohms measure the resistance across F96 as follows :

Across 1 and 2
Across 1 and 3
Across 2 and 3

Polarity doesn't matter - just post the readings you get. If you know the atmospheric pressure at the time of test then that would be neat info too.

Cheers,

Paul

[Pete_RS2]

Paul,
Here's the readings (in kOhms) I got from mine and Alistairs:

Pins: me - Alistair
Across 1 and 2: 1.635 - 1.144
Across 1 and 3: 3.07 - 2.56
Across 2 and 3: 2.44 - 2.423

I put Alistairs sensor in mine and went for a spin and by seat of the pants I think it did feel better. I guess we'd need to test with VAG-COM to see for certain if the ECU is still not recognising WOT ?

[S2central.net]

Bingo - that will be it alright... These results are wholly consistent with the differences measured between Jim's and my F96. Note how close my results are to Alistair's and yours are to Jim's -

Pins : Jims - Mine, in ohms
1 & 2: 1516 - 1200
1 & 3: 2890 - 2610
2 & 3: 2420 - 2410

You should now be seeing 1.4bar in overboost until ~4000rpm. Best tested with WOT from below 30mph in 4th.

I love it when a plan comes together

Paul

[Pete_RS2]

That's good. I'll order a new sensor then & see what boost I get when my boost gauge turns up week after next They're £41.62 +VAT from Bosch.

[GandalfS6]

I was checking my throttle with VAG-COM this weekend and it also does not give me WOT (Throttle angle between 8.3 and 85.4).

The atmospheric pressure on my car stays at 836mBar (just thought that was coincidence).

I took the F96 out (BTW the atmosperic pressure remains at 836 even with it unplugged) and here are my readings:

1 & 2: 2.99 (much higher than anybody else???)
1 & 3: 2.94
2 & 3: 2.42

Meanwhile the real atmospheric pressure (at the Airport 15km away) is 1025 hPA (apparently the same as mBar).

So I guess mine is fooked too! I'll see tomorrow how much I get ripped for a new one

[S2central.net]

Yes indeed - for reference purposes it was 1008mBar on Saturday when I tested mine and Jims.

Paul

[jameswkr]

FWIW here are my readings:-
(1 and 2 ) 1317
(1 and 3 ) 2700
(2 and 3 ) 2420

Forecast pressure 1012mb ( darkest Surrey ). James

[GandalfS6]

Guess what! Bosch South Africa don't know about the part and Audi wants GBP 98 :eek2: and they don't have stock - as usual! It is probably cheaper for me to import the part from the UK and it will be cheaper and quicker than buying from Audi SA

[jameswkr]

Is it not possible to strip the top of the unit and solder in the "correct" resistances? You wont have the high altitude protection but you should get your boost back.

[blu_s2]

or perhaps a variable resistor for a cheap and and cheerful boost controller