Johncee

Sounds very much like the problem I had. It'll drain the battery if it happens when you aren't around to hear it, and do whatever makes it stop. If you can do an OBD scan, the fault code that indicates a relay problem is P086B.

In case it's any help to anyone in the future, the cause of this problem turned out to be a faulty relay (the 645 one in the engine bay fuse box), which was discombobulating the ECM. Did a Carista scan, searched the fault code in this forum and found that a very helpful user called Bob3 had experienced and sorted the very same problem.

Don't think it's to do with dpf regen. Although I'm happy to be corrected. This doesn't seem consistent with the fan coming on randomly sometimes when the car has been sat on the drive with the engine switched off for hours. Also nothing to do with lack of use. Last time it happened was yesterday evening, a couple of hours after a 120 mile motorway drive. The fan came on, and wouldn't stop until the battery ran out of juice... It's a very intermittent thing. Can go for weeks without this happening. I fear this will make garage diagnosis a nightmare, unless this is a well-known problem...

@MartiniB Thanks for the info. The intensity of the noise made by the fan is similar to your video in the thread you linked to. But mine does this even with the engine switched off.... It can be sitting parked, completely turned off, engine completely cold and "whoosh" off it goes at random.

I did look there, but only saw the options "report" and "share". Maybe because I'm a newish member?

"no discovered" = "now discovered"

Been having problems with battery on my 2017 2.0 diesel recently: it's had to be jump started several times in the past 3 weeks. I've no discovered the problem: the radiator fan coming on very fast, and randomly, with the engine switched off. This can happen even with the engine completely cold after being stood for hours. Any experts have any ideas what could be causing this? Cheers!

Thanks. So not a DIY job then...

Hi Can anyone give me a step by step guide for replacing the battery on a superb 3 exec model? ( I mean the procedure for pairing the new battery with the onboard electronics. I know how to do the spanner work) Thanks! John