I’ve been having a problem with my front windscreen wipers just stopping for no apparent reason while they’re switched on (I don’t mean the ‘intermittent’ function – this is in both normal and fast ‘continuous’ modes).
Having read the workshop manual I know that the wiper mechanism has a ‘blocking protection’ function which cuts the power to the wipers if they’re switched on and there’s no wiper park signal received by the Body Control Unit for a period of 16 seconds (e.g. if the wipers are frozen to the windscreen or something physically obstructs them from moving). The BCU then only turns the power back on again after waiting 3 minutes or if the ignition is turned off & on again – and sure enough that’s exactly what mine do, although neither waiting for 3 minutes or keying off the ignition is much of an option at 70mph on the third lane of a motorway while passing a truck that’s throwing up huge quantities of spray.
Although I always believe that an ECU is the very last thing that should be blamed for a fault I thought I’d better first check that it wasn’t sat in a puddle of water or something due to a leak. I removed the passenger seat to inspect the BCU and its connections and everything looked absolutely fine.
Body control unit lives under passenger seat
I used my Faultmate to check for DTCs for the Body Control Unit and sure enough it had stored “Wiper motor blocked, park switch or wiper relay defective”. The wiper relay only costs £5 so I thought I’d try that first
Wiper relay is mounted next to transfer box ECU behind the battery