Help! ABS Woes... 96 B4 Teves 20 ABS/EDL

This turned into a long post, so sorry... but any help would be great. (This is on a GLX, but the ABS is common to TDIs, and I know some smart people hang out here)

I'm getting pretty close to taking our car in to a dealer to deal with this, but don't really have that kind of money to throw at it. We just moved to Texas and inspection is comning due this month, where the system has to be working at least enough to turn off the "Brake" warning light. ("ABS" light alone will not fail the inspection.) Both are lit (Brake light only in the last month) and sometimes the brake light goes out, but not reliably enough to get it inspected - the manual says this means there is no elctronic proportioning active, and braking performance is compromised.

ABS is on the fritz - the codes have been saying there were three intermittent/broken wheel speed sensors for a year now, which I just replaced last night, and it did not fix it *sounds of money flushing away* (OK- one wheel code has not come back). Last night it never worked and the codes would not stay cleared. But, for about 5 minutes this morning during a test drive, all the codes stayed clear and the system worked (I made 2 or 3 ABS-assisted stops with no problems) - for about 5 minutes, then while nearing home, lo and behold, the three wheel speed sensor codes came back again.

I've checked all the pinouts on the connector at the pump/control unit per the manual, and no errors there. Last night when I logged in to clear the codes after replacing the sensors, there were some other codes that I had never seen before - V64 Hydraulic pump voltage and some voltage supply ones, too. They didn't come back during test drives - only the wheel speed sensor codes.

I haven't been able to locate a source of any electrical fault in the harness or the sensors (resistance and current check out OK)... is my control module bad? I hope not - that's a $608 part at wholesale price.

Related topic, too: rear wheel bearing play - how much is acceptable? There is no limit in the manual. I have no perceptible endplay, but both rear wheels have a little wobble that you can feel only with the tire mounted, more in the "camber" direction than the "toe" direction. I dare not tighten the bearings any more, for fear of binding... (or exceed the preload per the manual such that the thrust washer can't be moved without prying). Both rear sensors are throwing intermittent or no signal codes, but also one front one (whose wheel bearing is fine). I don't believe this is the source of the problem, but you never know...

Anyone have any suggestions? I'm about to throw in the towel and call my freundlichen (dealer)...

Thanks,

when you drive the car and monitor (via VAGCOM) the wheel speed sensors for an extended period, do things look normal? Are you getting speed readings at all 4 corners?

If the sensors ain't the problem, it gets real expensive from there....

I assume you cleaned up the encoders at each wheel when you popped the new sensors in???

It would be extremely odd to have 3 sensors go out at the same time.

Dorf, thanks for the quick reply...

I cleaned the rear stutter ring as best I could with compressed air through the sensor mounting hole - the fronts looked fine, and I only replaced one rear sensor. (these have been going bad progressively over the last year - it started at the front right intermittently, then now it is three of four)

I didn't have a chance to monitor wheel speeds for an extended period because my laptop battery is also going south... but, I had problems last night seeing some wheel speeds (intermittent again), but this morning they all looked fine - at least while it was working.

My laptop shut down before I could look at it again when it quit on me.

In the past, they have been intermittent when viewed with Vag-Com. Before deciding to order parts, I checked that things were clean, and observed that the offending wheels were slow to register when the car started (sometimes at all), but usually they registered motion.

Checking them with a multimeter turned up widely varying vlaues, but all still within tolerances, so I guessed they were just not close enough for the control module's liking and decided to try replacing the cheap parts first.

How clean do these things have to be, really? I mean, they are all out in the elements, and a little dirt shouldn't hurt? The rears may be a little corroded (we live in the southwest though, where nothing rusts badly), but that doesn't answer why the front is on the fritz.

Background - car has ~200k on it, and has had rear brakes done once, and I re-used the ABS rings.

They should not need to be "like new", certainly. But, you'd want to ensure that there was no apparent damage, nothing bent, etc.

Isn't there a gap measurement that can be checked? I vaguely recall something like that in Bentley.

dieseldorf said:

They should not need to be "like new", certainly. But, you'd want to ensure that there was no apparent damage, nothing bent, etc.

Isn't there a gap measurement that can be checked? I vaguely recall something like that in Bentley.

Click to expand...

Yes, in the troubleshooting section there is a note to check wheel cleanliness and the gap, but I can't find a value for it anywhere in Bentley.

Maybe Jon or Chris will chime in....

Brief update before bed: Signals from the wheel sensors are definitely intermittent. Got my laptop charged again (old laptop with short battery life - hoping they'll buy me a new one soon) and did some checking on the way to the movies and back again tonight.

Three wheel speed sensors (RF and both rears) are almost always showing the short/open circuit fault during self-test after the ignition is turned on, they are showing intermittent signal, and the LF even came up with a mechanical fault (unusable signal) message once. Strange. The only one that seems to be working reliably is the front left, besides the one fault. The others sometimes will not show a speed at all, and then once in a while they will all work fine, but not for long.

If I get a chance tomorrow, I'll double-check the rotor/sensor gaps and cleanliness, and the ABS harness connections, especially those to ground. Something is not right for sure.

Anyone know what the airgap should be? Bentley doesn't say... except to check for proper bearing play and non-bent or non-broken parts.

What was the solution to this problem ?

Still haven't found the cause. There's a little play in the rear bearings - not what I'd consider enough to affect the abs, but I could be wrong. That doesn't explain the front wheel being out of whack. My best optimistic guess at this point is a flaky electrical connection somewhere - maybe the ground, but I haven't found anything. It may be that the module is actually bad.

The issue has dropped significantly in importance for me since the tranny in the same car started dying - I guess you could say I fixed all the issues with a B5.5 upgrade.

What used to be the family car that was a "must fix" is now a project car waiting to be fixed, sold, or stored - in any combination.