LEON 2006 Sport TDI - high idle, cooling fans coming on and rear window de-fogger not working?!

[Will83]

Hey guys, newbie here with Leon issues - please help! (Seat Leon 2.0 TDI BKD engine Auto/DSG - no DPF)

Problem first occurred randomly about 6 months ago. Without warning the engine idle went from normal to 1000rpm and just stayed there. The only way of stopping it was to turn off the engine and restart. This would continue to happen but with no obvious affect to engine performance or drive ability. Over time it got more random and would high idle when ever it felt like it - no pattern or clues to why. Complete mystery. When it does happen the cooling fans come on automatically and only shut down when the engine is restarted. Over winter I noticed that when ever it does this high idle/cooling fan 'thing' - the rear winder de-fogger would not work. The button would just flash at me - but yet again, an engine restart would fix this temporarily.

OK, now on to what I have tried to do to fix this problem but with no success:

A local mechanic plugged in his VAG computer and left the engine running - no fault codes would show until the engine increased in revs and he pointed out a possible battery/voltage issue. He suggested a new battery and alternator would cure the problem.

On my way to get an used alternator, the parts guy/mechanic said it was highly unlikely to be the battery/alternator and advised that the problem 'sounded like' air blockage in the cooling system. I went along and had the thermostat changed and housing, slowly topped up the coolant and watched 'bubbles' disappear in the reservoir. Took the car for a test drive and the problem went away. Problem solved? No! It started again a couple of months later and I'm scratching my head (again)

Since the New Year I have put fuel treatment in the tank to clean the system but made no difference. As changing the thermostat and housing seemed to help, I figured I might as well change the sensor on the side of the housing too but with no joy. The last thing I tried was taking the battery off hoping it would reset any short term ECU gremlin.

I am really hoping someone out there is going to confidently say - "Yep this the problem and this is how you are going to fix it!" As you can probably tell, don't really know what's going on but open to suggestions and advise.


Many thanks!

Will

[Flash2]

Hello Will.

Check out the link below. It's a forum post by someone who had the same issue on his MK5 Golf (the VW version of the Leon). The high idle/cooling fan issue was due to moisture in the engine bay fusebox. It doesn't say anything about the HRW switch flashing though.

Jim.

Radiator cooling fan problem? - Crasher/a8 tech - can you help? [Archive] - VW AUDI Forum

[Will83]

Hi Jim

Thank you so much for taking time out to respond. You have given me hope! Now I got something to work with and an area I really hadn't thought of.

Any suggestions on how to safely check and clean the fuse box?

Thanks again!

[Flash2]

Well, the first thing to do is disconnect the battery neg terminal.

I had a VW Touran a while back that had water ingress into the engine bay fusebox because someone hadn't fitted the cover on properly. I assume it will be a similar box to your Leon.

From memory, you have to disconnect the wiring from the main fuses at the front of the box(note which wire goes to which fuse first). Then you unscrew a torx T30 at the top, center of the box (where the small fuses fit). The screw doesn't actually come out but as you unscrew it, it splits the top part of the fusebox from the base. There are electrical connections in there that might be corroded.

The water ingress on the Touran I looked at was really bad and I had to partially open the top section of the box as well and dry it out with a hair drier. But on that car the ignition was switching itself on and all sorts of weird thing were happening. I doubt yours will be as bad as that. The Touran was fine after it got dried out, by the way. That must have been about a year ago now too.

I hope you find something in there to explain your idle issues.

Jim.

[Will83]

Hello Jim

I hope you are keeping well. Been wanting to get back on here for over a week as my father and I carried out the work you suggested. We successfully removed and cleaned fuse box and any connectors in that area. The car has been perfect for over 2 weeks.... up until this morning! It started doing the same thing. Absolutely gutted really.

Looking back at your response, the one thing I didn't do was dry anything out with a hair dryer. I removed the top part of the fuse box, sprayed with electrical cleaner and cleaned whatever I could. Must be on the right track - it worked right - unless there is something else affected?

Think its worth trying again... see how it goes. Will be back soon!

[Will83]

Hey guys, if anyone reads this I am happy to say that the problem eventually went away. I did spray some electrical contact cleaner in the fuse box and just let it 'sink' in and do its thing - not sure if that was the cure but one day it just stopped high revving on idle and I have done short and long distance driving since then it has never come back. Happy Days!