abs light flickers on boost

[RichLV]

Did you try to plug VCDS in? If your car is 1993+ model year the ABS is diagnostable. I had same issue with mu UrS4, but since mine is 1992, I cannot diagnose ABS via VCDS. Disassembly showed that my CV joint ring gear is clogged and one of my ABS sensors is dead. If a sensor is bad, the whole ABS shuts off, and it also has a habit of starting to kick in on dry roads.

[UrS4boy]

Relationship between diff lock one-way valve and ABS system

Could it possibly be that the one-way valve in the vacuum line to the diff lock actuator under the back seat has gone faulty? Does the diff lock still work as it should?

Even if it turns out to be a cold joint in the ABS controller circuit board, a failed diff lock one-way valve would certainly impact the ABS system.

When that one-way valve fails, boost pressure makes it to the differential lock vacuum actuator and puts the diff lock mechanically "ON" (engaged). As it does so, the F100 diff lock engagement switch is activated. This in turn is linked to the ABS system via the E83 ABS switch (or equivalent). The ABS system reacts by turning itself OFF (not ON).

Diff Lock 101: http://forums.quattroworld.com/s4s6/msgs/170940.phtml

[220bhp]

Thank you Dave

[UrS4boy]

Thank you Dave

So in summary:

Symptom: You get on the boost and you see a flash from the ABS dash light. WTF??

Answer: Your 046905291A one-way pressure/vacuum valve in the differential lock system (UrS4 and 95 UrS6) has failed and needs to be replaced.



https://www.ecstuning.com/Search/Sit...291A/ES276312/