abs module losing communication during scan, and other "abs" errors. dying module?

[dansansome]

bare with me on this, im trying to give a bit of background...

a4 cab b6 2003, bfb engine, 1.8t manual front wheel drive.

I have been having issues recently with the steering angle sensor and abs lights randomly appearing on my dash, mostly accompanied by a dead speedo. if the speedo does not initially stop working, then any sustained period of being stationary (for say 10 seconds or more) will generally result in the dead speedo again.

(this fault also causes my electric seats becoming unresponsive using the handle buttons, and my cab roof not working).

the dash lights will always clear after 1 or more ignition cycles. and then all will work fine until the next time it happens. the lights generally appear when stationary fairly soon after braking, but not every time i brake to a stop, and very occasionally i get a little feeling of abs kicking in during low speed braking (that kind of grinding sensation through the brake pedal). the pressure applied when braking to a stop also doesnt seem to matter. i have tried feathering from slow speed, and really standing on them.

i decided to have another probe around using my ancient copy of vag com, and noticed that i can scan all modules, including the abs module (it opens the controller window, shows controller part number and coding etc), but the abs module reports that there may be communication errors, and the fault codes are not displayed - saying something like "dtcs may not be supported". the controller window appears to reboot a couple of times. old fault code scans that i saved on my laptop show that the abs module has been successfully scanned and no faults reported. (same laptop and cable etc)

would this indicate that i have a dying abs module, and the comms errors may be linked to the seemingly random error lights?

i have read up on this topic quite a lot, and have previously had a brake light switch dtc in the engine controller, but this doesnt seem to have come back since i cleared it a good few weeks ago. i have also seen a speed sensor intermittent signal (sensor g22) but then found that according to elsawin my cab doesnt have this sensor???

also i have read that changing abs sensors (as reported by fault codes) may not solve the issue as the module itself is knackered.

i feel like im going round in circles a bit with this, but the dead speedo is really irritating, so any help that anyone could give would be much appreciated.

[dansansome]

Well to answer the thread for those with similar problems, the comms errors turned out to be a knackered lead (it was an old "dumb" cable anyway, I suspect a few years of folding up etc killed it). A new lead communicated fine.

I replaced a rear abs sensor, got the same errors and symptoms.

Replaced and recoded an abs module I got from eBay and so far everything is behaving as it should!