X300/308 Heater circulation pump failing


No, it is not the brushes that are worn out. They are positively fine. I wonder though if I have ruined the pump by testing it without paying attention to the polarity… I noticed there is a single electronic component residing in the area, a diode.

When I put 12V over the terminals, all I get is a faint spark and not a running pump. Trying the pumps (I actually have three!) in the vehicle, they instantly blow the fuse when I connect them.


Kind regards,
Bard Thomas

If you connected it up incorrectly, then cut the diode out.

Are you sure its the pump fuse blowing, and not the relay control fuse for relay and front fogs.
If the latter, disconnect the alarm siren hidden in the passenger wheel arch. (or behind bumper) common problem

Hi Andy,
Not sure what you mean… And yes, I am quite sure it is the pump that is blowing the fuse. Maybe I was a little unclear; the diode resides inside the pump, on the commutator side.


The diode isn’t essensial. So if you have blown it you could cut it out, and have a spare/working pump.
or just to use for fault finding