My 2000 1.8 XEi has been laid up for a while as my we have been away. My son turned it over regularly so it runs fine, BUT, now, the ABS seems to be permanently on. Touch the brake pedal, it is hard and you can hear and feel the modulator working but actual braking is minimal. I have run the diagnostics and no fault is reported (disconnect a sensor and it shows immediately).

I have searched a couple of forms but this seems to be a new one .

Does anybody have any idea where to look ?

Check the wire for the abs, could be bad. I got on my ford front abs wire that on occasion will show on some left hand turns. Just a bad wire

If your diagnostics shows live data, you could examine what each wheel speed is showing to see if 1 has a fault that the diagnotics can't pick up.

It could be also be, as above, a wiring/connector fault where the brake switch feed is somehow raising the pin on the modulator to actuate the ABS, or possibly even a short inside the ABS ECU. If the car has been damp while standing, a conector (eg in the cabin) may have corroded.

Unplug the negative lead off the battery.
There's a multi connector on the ABS unit on the black plastic bit, or if you have the two part system, it's under the passenger seat.
Unplug the connector, push back towards the cabin(one piece unit) or pull out(passenger seat version)
Leave unplugged for 5 mins.
If you have the one piece unit, check connection for moisture.
Plug back in.
Reconnect battery (reset rear window!)
Try again.
Mike