Aux Water Pump

[henrym3]

Don’t work, so put 12v to it and it works. Checked plug voltage and it gets 4.4v? Can anyone explain. Can’t be a fuse or there wouldn’t be any power. Checked the power wire and good known earth and still 4.4v? Any suggestions while vehicle is in bits getting engine and gearbox oil change. Not fully aware of the roll it plays in the heating system as I’m not aware of any problems with the heating or a/c

[Greydog]

Hi Henry
As I understand it the Aux Pump runs to circulate hot water at low engine speeds or when idling, it is linked to the cabin temp controls so this may explain the odd voltage reading. Try ignition on temp settings high fan speed low to see if the fan runs, that's the only test I am aware of.
They don't seem that robust as I have replaced two now.

[henrym3]

Thanks for that Greydog, just been out and tried all different settings. No joy. It will I assume be more annoying in winter when parked or in a traffic jam, I’ll have to try and find where exactly it gets it’s power source from and what exactly triggers it on.

[henrym3]

So done some research on TIS and turns out the earth is in a cluster with steering column motors, front interior light etc etc and is located behind instrument cluster, as all of the other items work I can pretty much rule out the earth wire. The power comes from pin 9 on the heating and a/c module straight to pump, no fuse. So tomorrow I’ll remove module and disconnect the plug and put 12v to pin 9 on plug and see if pump runs.

[fenj66]

do you have a webasto auxiliary heater in your car?
i was under the impression the aux water pump was there to circulate the hot water from that.
perhaps the aux heater needs to be running to operate the pump.

[Greydog]

Not many petrol X5's with aux heaters that I am aware of mostly diesels. On my 4.6 I have replaced the aux pump twice once with a used one last time a new one. Following Henry's research I may have another intermittent fault somewhere !!! Damn

[henrym3]

No I don’t have an aux heater, just the pump, having thought about it, I have in the recent past replaced the heating and a/c module then the aux pump stopped working but I didn’t change that for some considerable time and I wonder if during that period that the effort it was making to try and work the pump has burned out something in the heating and a/c module. Not being electrically savvy enough, I don’t know. According to the wiring diagram there is no fuse for that live feed but there must be something that gives if and when the electric pump is seized. Which was the case when the old one was removed.

[Greydog]

If it was simple BMW's devious designers will make it super complicated somehow!!