Brake Pressure Warning on E34

Recently had a 'BRAKE PRESSURE - OWNER'S HANDBOOK' warning on the dash of my 1993 530i. combined with a red light on the dash. I don't appear to have
lost any brake fluid, and the brakes feel fine. The warning comes on intermittantly every 10 secs or so whilst driving, then disappears.
I don't have the owner's handbook unfortunately. Could anyone tell me what triggers this warning?
Regards,
James
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Could be the hydraulic pump that drives the servo (rather than vacuum as on most cars) and PAS. Check levels all round. Check for loose wires to sensors on brake fluid reservoir etc. Does the warning come on when you are turning the steering wheel when parking?
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