I have seen numerous ABS hydraulic actuators cause this problem but electronic control has never been the issue and disconnectingt the electrical would have done nothing on any of them. If it did it probably would set a light.

The way to find it is to crack loose the hydraulic line in various places till the brakes release. Since it is so intermittant that will be difficult. On a couple of the units that were bad we were able to deduce the problem by electrically activating each solenoid. The one causing the problem was always quiet and probably stuck.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician