Brake pressure sensor

[ChrisA]

I can’t believe my own luck sometimes!

On Thursday I start stripping down the 300zx to get to some faulty injectors. Doesn’t matter, it’s winter and I won’t put her back on the road until spring.
So this morning we “the family” all jump in the wife’s Skoda to trundle down to Arundel wetland for an afternoon out. After a few miles I notice that the car feels a bit odd and pull over to find the off side calliper has sized on.
Get back home without much fuss and jump in the Audi to carry on with the afternoon out (I’ll deal with that brake tomorrow). About the same place I pulled over to look at the Skoda the to ABS and warning triangle light flash up. Just before the light came on, around 1-2 minutes, I did hit a big pot hole on the a27.
I’ve done a scan and the following error is logged. I’ve cleared the fault but it does pop back on straight away.

Any ideas gratefully received.

[Shoppinit]

Best case, the brake switch is faulty. Check it with the Vagcom. Another good case, the wires have popped off the pressure sender on the ABS pump.

Worst case the impact ripped a tiny gold pube wire off the ABS module circuit board.

[ChrisA]

Thanks Shop.
Do we have guides on how to perform these kind of tasks with VCDS? I’ve been googling how to use VCDS and I’m hearing a lot of stuff but none of it is really going in. Or is it best to just sit in the car, plug it in and play around with it?

[Shoppinit]

Yeah, plug it in and go through all the measuring blocks for each module. You’ll see what’s available.

You can look at the adaptations, too, but be wary of changing anything.

Steer clear of basic settings until you’ve got more confidence or are following a specific set of instructions.

[Shoppinit]

For brake switch, for example, you can check the info is getting to the TCU and ABS module. You’ll see the status change in real time as you press the pedal. Or not as the case may be.

[ChrisA]

So I’ve had a look with VCDS on groups 2,5 and 9.

On group 2 brake test and light switch both activate when I press the brake pedal and parking deactivates when I release the hand brake. The only bit that looks a bit strange on this group is that ASR/ESP won’t stay activated. It does activate when I press the button but won’t stay on. I’m assuming this is because I’m in test mode rather than it being an issue?

Group 5 has a resting brake pressure of 0.00-0.65 bar. This increases to around 130 bar when I stand on the brake (when parked obviously).

Group 9 also has a pressure reading that stays in line with group 5 reading. It also has two other reading that activate when I press the brake pedal but no units are give.

I’ve also taken a look at the ABS pump but can’t see any obvious issues.

I’ve had a look at the “Adaptation-10” folder but it doesn’t seem to have anything available on any “Channel”.

[Shoppinit]

Yeah, there's no adaptation channels on the Bosch 5.7 ABS module.

Interesting that your pressure readings seem coherent but that you can't reset the fault code. If you reset the code with the engine off what happens? Does it come back immediately? What about with the engine on?

Have you checked your brake lights? Those switches are notoriously rubbish.

Can you look at the measuring block for pressure under different conditions with the engine running? See if at any point it goes to 40 or 290.

[ChrisA]

I can now clear the codes with both the engine off or on. But before VCDS has finished scanning the whole car the warning lights pop back on again. If I select “address 3-ABS brakes” it clears the fault only to find it again.

All 3 brake lights come on.

So I fired up the measuring block again for group 5 and 9. Now they’re both reading 291bar, the brakes aren’t on and the pressure reading is constant weather I’m the engine is on of off, driving or not.

[Shoppinit]

Yeah, 291bar can't be good. That's why it's putting a code on. It's an incoherent value.

I fear that your ABS module is borked.

[ChrisA]

Yeah, 291bar can't be good. That's why it's putting a code on. It's an incoherent value.

I fear that your ABS module is borked.

Bugger! Oh well, I’ve had 6 months of relatively trouble free C5 RS6 driving and that more than some folks have in a life time.

I presume it’s worth buying these new rather than used, are they a pain to get to (please don’t tell me it’s an engine out job) and is it a diy job?

Just found this...
http://www.ecutesting.com/catalogue/aud ... &model=824

https://www.audiworld.com/how-tos/a/aud ... ule-421239

[Shoppinit]

You'll struggle to find a new one without the whole pump assembly for megabucks. I found one for a 5 series ones at Autodoc. Might be worth contacting them.

The repair services tend to get mixed reviews but is probably your best bet. Have a search on here for them.

[Mɐʇʇ]

I feel for you Chris. Have had it many times, one car breaks so you switch to the other which then breaks as well just to make sure you really feel it.

[ChrisA]

I feel for you Chris. Have had it many times, one car breaks so you switch to the other which then breaks as well just to make sure you really feel it.

Thankfully it’s looking like an easy fix on both the Audi and Skoda. At least I can still use the Audi while a wait for a window where I can take the car off the run to get the module out and off for repair.

The 300zx is looking anything but simple. I finally got the plenum off after about 8 hours. It looks like, ontop of replacing all the injectors, I’ve got a lot of brittle hoses to replace and could really do with replacing the main harness. Can get the early style harness any more so I’ll need to upgrade the CAS and PTU.

[ChrisA]

Am I missing something painfully obvious here? I’ve disconnected the two electrical connections and the two retaining clips yet I still can’t bring the unit up enough to access the 6 torx screws to separate the module from the ABS unit. What with the pipe work on top of the unit going off in all directions it seems like you would have to put a lot of stress on these pipes to make it move.

I think removing the wheel and arch liner would give enough access to the lower two torx to get the module separated from the unit.

[Mɐʇʇ]

I know this'll sound weird, but look at those lovely long runners into the plenum. Good design.

Thankfully it’s looking like an easy fix on both the Audi and Skoda. At least I can still use the Audi while a wait for a window where I can take the car off the run to get the module out and off for repair.

The 300zx is looking anything but simple. I finally got the plenum off after about 8 hours. It looks like, ontop of replacing all the injectors, I’ve got a lot of brittle hoses to replace and could really do with replacing the main harness. Can get the early style harness any more so I’ll need to upgrade the CAS and PTU.


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