Try swaping the relay for the hydralic unit. it is labeled in the fusebox,the one for the ac compressor is the same just swap them and try your test again, the realy will sometimes get damaged by the pump when the amp draw of the pump is too high. sometime the relay will fail and the pump will be fine, try that and let me know what happens. there are also some problems with the pressure sensor in the bottom of the brake master cylinder, which are cheap and easy to replace, and every now and then I find bad yaw rate and or acceleration sensors.

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97 e320 200k!

85 300sd

96 c280 sport for parts! pm your needs