HELP! - Intermittent fan fault no one can diagnose (draining the battery)

[Pilchhall]

Hello all,

 

I'm in desperate (and frustrated) need of help.

 

I have a 58 plate (2009) Skoda Superb 2.0 TDi Elegance which I've owned for 7 years and until recently has never given me a single spot of bother - I love it.

 

However, I recently discovered an intermittent fault with the fans that was completely draining the battery.   The fans are coming on full power at completely random times when the car is switched off (even when it is completely cold and hasn't been driven for a day or two - so it's not the DPF regen ).  The keys are out of the ignition, the car is locked up and randomly the fans will come on.  It might be straight after turning the engine off, or it can be hours (even days) after I've turned the car off.  It seems completely random.

 

It's been into my trusty local garage (not main dealer) a couple of times and my mechanic is totally stumped - no fault codes etc.  He's tried a couple of things when it has done it, but no luck in diagnosing it.  I even took it to a German car specialist, he had it in for three days but it didn't do it once (cost me £100 for the privilege of him having my car for three days and scanning it).  Got it home and a day or so later I heard the ominous sound of the fans firing up from my driveway.  I can't really afford the time without the car leaving it with the German car specialist for a few days a week (or to keep chucking away £100 each time if it doesn't do it), so I'm turning to you guys in the hope that someone might be able to help me?!

 

My current situation means that I have to pull the fuse that controls the fans every time I park the car, so that I can be sure I won't have a flat battery when I return.  As I'm sure you can appreciate this is incredibly annoying when you're doing school runs, in and out of the office, or the supermarket etc.  It's also already cost me one snapped bonnet release lever!

 

My mechanic told me he thinks the fan control unit is built into the main fan (there is no fan relay) and so to replace that you need to replace the whole fan, which is somewhere around £400.  That's a lot to fork out in the hope that it might solve the problem, without any guarantees, so I'd rather try and be certain that whatever we do (and whatever that costs) is going to solve the issue.

 

Willing to listen to any suggestions, ideas etc. that might solve this issue.

Thanks all - I'd really appreciate any ideas, thoughts, advice etc. on how I might be able to solve this problem.

[Breezy_Pete]

Have you inspected the wiring adjacent to, and connector going onto the main fan? Will try to find relevant circuit info in a sec.

 

[Breezy_Pete]

The wiring is pretty simple.  A thick permanent 12V (black) and earth (brown), then a thinner ignition 12V feed and a 'command' wire (green) from the engine ECU. 

Only checks I can suggest to try to exclude the fan itself is for wiring breaks near this connector and/or corrosion/ingress signs that might be causing unwanted connectivity or lack of.

[Pilchhall]

Thanks ever so much Breezy_Pete.  Pretty sure my mechanic said he checked all the obvious connections/wiring - but I'll double check this evening and report back.

Cheers.

[J.R.]

Is there not a Fan Controller module Pete?

 

The mention of a "command wire" makes me think that at the very least there will be a relay of some sorts.

[Pilchhall]

Thanks J.R. and I'll let Pete come back on this too, but my mechanic thinks the control module is built into the fan unit itself - therefore no separate relay in the fuse box - and if the control module is buggered, you have to replace the entire fan unit.

Cheers.

[Breezy_Pete]

11 minutes ago, Pilchhall said:

the control module is built into the fan unit itself - therefore no separate relay in the fuse box - and if the control module is buggered, you have to replace the entire fan unit.

Yep.

Unless the control module within the fan could be repaired, which might be an interesting project.

I feel I may have seen someone have a go at this with some success, probably on another forum.

Odd that it's intermittent though.

Do the fans ever seem to kick in full speed unexpectedly while driving, or only ever when the car's off?

 

If you do end up replacing, I might be interested in post-morteming the old fan, so please ask your garage to hang onto it rather than skip it. 

 

I'd say it seems to be a fairly rare failure, so a secondhand unit off ebay with perfectly matched part number might be worth a gamble. Is there a part number visible?

You could even maybe connect up such a purchase without fully installing it, and see if it does or doesn't misbehave when the car is off before spending on fitting?

 

 

 

 

[Nackuk]

While this isn't going to be the answer to your problem maybe it will help you solve it.

On my Mk1 I had the fans come on and they came on like jet fighter engines. They would always come on when the ignition was on. I looked at many things, the electrical schematics, the so called control modules that are brought up on the web. But nope i could not work it out. A licenced VCDS would not see an error code either. Now I can't remember how I worked it out maybe it was the the simplest thing to change in the electrical schematic, but it was in fact the air conditioning pressure sensor failed but in state that meant no error code had come up it was just asking for the fans to come on max. I swapped it and the issue went (luckily the sensor was on a Schrader valve).

 

Maybe have a closer look at the DPF pressure sensor or temp sensor.

[Pilchhall]

Thanks Pete - I can't say I've ever noticed them kick in whilst driving, it's only ever been when the engine is off.

 

I'd personally thought about going down the second-hand route, particularly if we hadn't been able to absolutely, 100% determine the fault beforehand.  If I do end up replacing, will be sure to hold on to the old unit and let you know.  Like the idea of testing a replacement without fitting too - although not sure where that would leave me, certainly without a driveable car (although potentially a fan unit I can return, I guess).  I'll have another look at the wiring later and see if I can see a part number at the same time.

 

Thanks Nackuk - I'd read elsewhere about people having issues with their fans that were linked to the air con pressure sensor and I think my mechanic had a look at that.

Excuse my ignorance, but why would the DPF pressure sensor come into play?

Cheers.

[Breezy_Pete]

10 minutes ago, Pilchhall said:

see if I can see a part number at the same time

I can look it up if you were to message me with your VIN; probably easier!

[andrehj]

21 hours ago, Breezy_Pete said:

The wiring is pretty simple.  A thick permanent 12V (black) and earth (brown), then a thinner ignition 12V feed and a 'command' wire (green) from the engine ECU.

In that case the check is pretty straightforward. @Pilchhallcan simply measure the voltage on the command wire when the fans run with the car off. If that is the case (which I suspect it is), the problem is not in the Fan module, but somehow the engine ECU switches the fan on.

It may also be a drowned ECU which is causing this problem, similar like the Passat in this video (scroll to 5:44 and turn on the subtitles if you do not understand German):