ABS and Brake warning lights on speedo out

[570ek]

Hello,
My 1999 V40 2.0 T SE Auto has started a new problem. We have owned it since new with a full volvo servcice history and its done 75K miles.
Whilst driving the ABS and Brake warning lights come on together and at exactly the same time the speedo dial goes to zero and the mileometer stops working. Turning the ignition off and on sometimes clears it or it will clear itself whilst driving.
I have taken it to the garage and they tried to read the computer for a fault number in the ABS system. Whilst the warning lights were on the computer wouldnt allow access to the ABS system but the engine and transmission were accessed and no fault codes appeared.
Then they did manage to access the ABS system when the warning lights were not illuminated and no fault codes appeared.
Two garages are scratching their heads and the main dealer has not been contacted yet. Before I do anything can anyone point me in the right direction please.

[sebaveh]

I'm pretty sure there are bad connections on your ABS module. Module is located around ABS hydraulic block, take it out, disconnect and look for any corrosion or other unlikely marks. Also check the wheel sensors and wire harness.