First port of call - its nearly always a wheel sensor or sensor connection.

Check the connections under the bonnet (white plastic connectors that sit on top of the rails) first if I were you. Lift the rear seats and you'll find the rear pair easily.

Pull them apart and clean them up... or maybe even simply reconnect them and test each in turn if you are in a hurry - you can always return to the dodgy connection when you know which one it is.

Next step would be to remove each one in turn and check for crap. They can be tight so once the bolt is removed twist until the O ring seal frees up.

If you still have no joy check the control unit under the dash - rarely hear of them being a problem.

Last of all you will need to either test each sensor or replace them in turn. front and back are different unfortunately.

I had very similar issues a few months back and a clean up sorted it thankfully.

Think Tabs or someone on here knows the resistance test for the sensors.

Anyone else got any ideas?