Diff lock to ABS connection?

[domas]

well you never know how that pin controls abs kill function. maybe you need to ground it or pull it high to let the ecu know that abs should not be killed. just an idea.

[UrS4boy]

well you never know how that pin controls abs kill function. maybe you need to ground it or pull it high to let the ecu know that abs should not be killed. just an idea.

Based on what the F100 Diff Lock engagement switch does and its connection to pin 13, I would say grounding out pin 13 = ABS off.

[Glen Chamberlain]

I'm quite confident now the ABS issue is not related to the Diff Lock situation. I am now running out of things to test or check apart from buying a used ECU to see if that changes anything?

[domas]

try this:
connect pin 31 directly to diagnostic interface k-line pin. It may be grounded/shorted somewhere.
Else, try another ecu.

[Glen Chamberlain]

Ok thanks,

I have bought another ECU so i'll give that a try and report back. Hopefully it will be here by Friday!

[Glen Chamberlain]

ECU has arrived today and we have a little progress but not yet solved the issue.

Old control unit 4A0 907 379
New control unit 4A0 907 379 A

First of all note the additional "A" on the new control unit. I check with local TPS and they said the A was just a later variant but still essentially the same unit?

Now the ABS light still stays on but it flickers slightly when you first put the ignition on which it didn't used to do, I guess it is now doing the self check.

I also now have comms with VAG-COM to the ABS ECU.

Code 00289 - ABS Inlet/Outlet Valve: Rear Right (N140)

I am struggling with the DTC because I didn't think the car had independent rear left and right control ABS control.

The diagrams I have show solenoids N58 & N59 for the front and N77 for the Rear? This DTC is suggesting solenoid N140?

I am wondering if the "A" on the new control unit is configured slightly different where it is looking for a solenoid resistance down some ECU pins that aren't used on my car? Trouble is I cant get any coding out of the old ABS ECU as it was uncommunicative?

Any ideas would be gratefully received?

Thanks
Glen.

[domas]

Code 00289 - ABS Inlet/Outlet Valve: Rear Right (N140)

what was the line under it? code is not enough.

[Glen Chamberlain]

Sorry, 35-00 - -

[Mikes2]

That 4A0 907 379 A is for fwd cars

[domas]

that explains the code as FWD cars have 4 channel ABS for some reason. I do have a very difficult time understanding why quattros have 3 channel only

[Glen Chamberlain]

Well that's helpful guys thanks. Probably just an ECU issue to start with. When I fit the correct ECU all should be ok? Fingers crossed!

Thanks

[UrS4boy]

ECU has arrived today and we have a little progress but not yet solved the issue.

Old control unit 4A0 907 379
New control unit 4A0 907 379 A

First of all note the additional "A" on the new control unit. I check with local TPS and they said the A was just a later variant but still essentially the same unit?

"Local TPS" is full of s**t. 4A0907379A = 2 wheel drive C4 100s, b3 80s sedans and coupes and ACA cabriolets.

4A0907379 = 93-94 C4 A10Q, b3 (A80Q) sedans and coupes and the RS2s.

that explains the code as FWD cars have 4 channel ABS for some reason. I do have a very difficult time understanding why quattros have 3 channel only

Because the rear wheels on a quattro are connected by a differential, not totally independent like the wheels at the end of a beam axle.

[domas]

yeah right. so does front axle.. it has a diff in it.

Nah but there must be a good reason. Maybe something to do with locker in older models.

[UrS4boy]

yeah right. so does front axle.. it has a diff in it.
Nah but there must be a good reason. Maybe something to do with locker in older models.

Locking the rear diff turns off the ABS.

The rear reason is cost:

"There are two main types of modern ABS systems: three and four channel. Three channel systems control the braking pressure on both front wheels independently, but control the rear wheels together as a single unit. Four channel systems (as shown in Diagram 1) control the brake force on each wheel independently (assuming you're in a four wheeled vehicle!). In three channel systems, although both rear wheels are monitored by sensors, if wheel lock if detected on a single wheel the hydraulic braking pressure is reduced equally on both wheels. This does not provide the level of control of a four channel system, and thus three channel versions are compromised and usually only fitted to cars to save on cost. Most modern cars now use a four channel ABS systems which provide greater safety in emergency braking conditions."

REF: http://www.drivingfast.net/technology/abs.htm

[domas]

I am very well aware of the facts: turning the abs of by difflock and what is the difference between the two as I do own a 3 channel vehicle. But my main concern is what does it have to do with quattros.

Lets say it is a cost saving thing. Adding 1 mechanical regulator vs 1 extra valve in ABS unit is .. well.. strange. I don't think it is cheaper in the end. But anyhow, if it is cost saving thing there must have been an eco option when buying cars where you could opt for any of the two systems. Why does it correlate with car being fwd or q??! You did not get your cars delivered with, lets say, steel wheels instead of alloys to save on cost in case it was a quattro. Thus I fail to believe that it was a cost saving thing.