Had this on my van just out of warranty unfortunately it was the abs pump - in addition to the light show the speedo had packed, up nothing logged in the ecu a change of pump at £1000 fixed the issue but that was after a lot of fault finding with abs sensors etc. When i took it to the dealer asked the question do you see this issue a lot and the answer was "never" went back to pick it up and there were 3 more boxers awaiting replacement pumpsWhen we first picked up our present Peugeot Boxer based van it had been standing unused for some 18 months plus due to the previous owners ill health and on the way home from picking the van up the I had the warning light come on as I braked coming down the slip road off the A1 a few miles from home. Thinking it may have been caused by heat from long heavy braking down the slip road I gave it a couple of hours to cool down and checked the fault codes. From memory the fault code came back as the ABS did not receive data from a sensor within "x" amount of milli seconds. I cleared the fault codes and went out for a test drive and the warning light came on again.
To cut a long story short a bit of digging around on the internet came up with 3 main causes of this problem. In order of cost, damaged wiring to one of the ABS sensors at the wheels, a dirty or corroded/rusty ABS ring or a dirty/ corroded connector in the ABS wiring. Next a faulty ABS sensor and the biggy for cost, a faulty ABS pump.
I unplugged and cleaned the terminal on each of the connector in the ABS wiring from the sensors at the wheels and luckily this cleared the problem and it has not returned since.