L322 EPB not staying on

Good morning all
I have a 2007 RR L322
The EPB module will operate and hold car whilst I hold the small switch / lever up
As soon as I release lever - brake also releases
I have changed the switch and had a used ( but I believe) working module fitted by friend
Does this need setting up or have I simply bought a duff unit ? many thanks in advance
Jim Tavender

Welcome. First question, would most likely be: what does the diagnostics say?