ABS faults are usually caused by the failure of one or more of the four wheel sensors or their reluctor rings.The front ones fail much more often than the rears.
IIRC the ring on the 307 is a magnetic strip fitted to the wheel bearing. If the bearing is worn this can throw up an ABS fault.
However, there are a number of other causes such as pump or ECU failure.
Check for obvious faults such as-
worn wheel bearing
damaged wiring
a cracked, excessively rusted or missing reluctor (if I'm wrong about it being on the wheel bearing it will be on the drive shaft).
damaged, loose or failed sensor. If you have a multimeter you can unplug each one and check/compare the resistances.
If you cant see anything you'll have to get it plugged in to diagnostics. Many independent workshops can do this, but make sure you tell them it's the brakes, as some generic readers can only do engine systems.
There is no point fitting new parts at random.
brewster
November 2009
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.