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Retro fit of OE towing electrics & upgraded 600w fan

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It’s taken me months but I’ve finally put the car back together properly now, so thought I’d share the pictures & some info just incase it’s useful for anyone else. 

The main delay was the AAG control unit, the semi connector shortage put a massive delay on BMW Germany getting one in. They are available second hand but my main dealer didn’t want to code in a used unit. I fitted everything myself, getting them to agree to doing it that way was a little tricky, the official fitting instructions aren’t meant to be available to the general public, but they are happy to sell you the parts! Luckily my friend works in the warranty department there so she got the instructions for me. 

The original official instructions for the detachable & electric retractable towbars both say you must change the cars cooling fan & the main power cable:



(SA 8SL is the trailer preparation option, I assume including the 600w fan. 
Note also it only mentions the B58 engine for the fan, that’s what the 540i has) 


There are actually some new retro fit instructions for different detachable Oris towbars that don’t mention anything about cooling fans or power cables:



They seems great on first look till checking the specs, that towbar is only licensed for a 75kg nose weight & 750kg trailer weight, instead of the normal towbar at 90kg / 2000kg.

My empty car trailer is 500kg. 

It seems BMW decided 750kg trailer is the limit for the standard 400w cooling fan. 

I wanted to pull my car trailer with a car on it & a caravan occasionally (we have kids!) so decided to bite the bullet & got the £250 odd battery/ power cable. Its a big job to fit needing the fuel tank & subframe dropping a bit to do it. 

Luckily before I had really taken anything much off I noticed the new cable looked suspiciously similar to the one on the car so I checked the sizes:



Exactly the same! 

The part numbers were actually slightly different:



So I then searched for the parts numbers my self & could only find the part number of the new cable. So I asked the BMW parts guy, he couldn’t find any other part number either so he agreed that there is no such thing as an upgrade cable. As he put it, “If I asked for a standard replacement for my car I get that same cable” so he gave me a refund on the expensive “upgraded” cable. Neither of us can work out what on earth the official instructions & retro fit parts pages are on about. Maybe some of the earlier smaller engined cars had different cables but they certainly only have one type available now & our 540i had one of the exact same diameter. 

The fan its self was a very easy swap compared to an E39 viscous fan!


The standard fan is 400w you can check by just looking down the back of the fan after opening the bonnet:


I got a new 600w fan from Autodoc as it was just over £400 rather than somewhere north of £600 from BMW for the same thing. They are Mahle fans so the same one is available after market:




They just cut off the BMW logo half of the sticker!






4 different fans available! The G31 540i only needs the 600w (in the UK at least) for towing. 




They looked different but actually both the 400w & 600w fans have the same size insulation at least…


… however the car side of the fan wiring has much thicker cables, possibly ready for up to the 1000w fan? 

Interestingly the car didn’t throw up any errors about the different fan being fitted. I told the dealers I’d put it in, just incase the towbar retro fit coding sequence asked about it, but they said it didn’t & there weren’t any stored errors about the fan either so they assumed the car can just tell what fan it is it’s self - great for anyone else who wants to fit one! They must use brushless motors by now, the two thick cables & two thin control cables would suggest it is, I’m no expert on them but have got a friend with PhD on the matter I could ask if anyone’s interested. He’d known what the chances are of the cars fan motor controller being able to detect what size the motor size was. I’m not too bothered as I had the full dealer retro fit coding done, if there were any hidden changes they will have been covered by that. 

The retro fit towbar electrics are just about the same for detachable & retractable towbars. The back end of the new harness plugs either directly into to retractable unit, the 13 pin socket is part of it, or just into the separate 13 pin socket for the detachable. The only other extra bit is the button for the retractable one, you just don’t use the plug for that with a removable one. 


That’s the removable wiring kit. 

This isn’t a step by step guide, it just to give an idea of what you need to do. The G30 will be similar but this is on a G31. 

You need to hold the luggage cover in just the right place near the bottom to make the tabs move to the top & stay there:



Then that cover & everything else on the side of the car to the front comes off:



You wouldn’t be wanting to change one of those fuses at the side of the road!

There are 4 wires that run to the BDC at the front, two for the R2 CAN bus & the other two should go directly into the BDC, however the locations for them were already taken so they have to be joined to the existing wires with the BMW “O” connectors:


The instructions didn’t say anything about doing this so I was pleased the master technician said it was what he’d have done too when I took it in for the coding!

If your fuse board in the boot looks like this:



You’ll need one of these:


With the extra fuse slots to the right for the AAG trailer control unit. Its also houses the different LIN module, the box with big 2 on it. The circled fuses are for taking the power to get a caravan fridge working, that’s in a different post.  

The AAG unit goes under the floor in a G31:


It not plugged in there & actually sits down flat in the holder that’s there ready for it, but if it was fitted in properly you wouldn’t see it!

The location info was totally missing from the instructions. Its apparently up on top of the wheel arch in a G30. 


I put a Westfalia removable towbar on, much the same as the one you’d get from BMW but about half the price. I’ve had retractable ones before & didn’t want another. The ball has to be clean & grease free for caravans to clamp on, it just goes rusty on the retractable ones, you can’t use a cap because the hitch sits sideways & it would fill with water. The removable one sits inside the boot & stays clean & dry. 

Here’s a few fitting pictures, it’s all very simple really. 



The original crash bar comes off & is replaced by the towing version:




I had been looking at some used ones as the westfalia was out of stock for a long time (luckily in the end it came back into stock before the AAG did) & couldn’t work out what all the brackets were for. 




Once fitted I realised side ones don’t do anything, on a 540i at least, seems they hold the exhaust hangers on some models. The 4 tabs that stick out down the length of the bar replicate the holes on the original impact bar so you can re-attach the plastic inner bumper part. 



It took me a while to work out the best position for the wire so it didn’t rub on anything when the socket is swung down. 

To get the wiring into the car drill & then pull out & cut the O/E bung as instructed to get the wires into the new hole. Once pushed back it looks like this:


Then seal:





Odd angle pic looking up with just the inner plastic bumper parts (before outer normal bumper went on) with the cut out now removed from the lower panel. 



All back together, obviously with the towbar removed it looks perfect normal so not really worth a picture!



If you arm the towbar so the key comes out it fits nicely under here (in its bag normally). 

The main dealer only charged for an hours labour for the coding but I actually ended waiting 4.5 hours! They had to update every system in the car to the latest software version before actually running the retro fit sequence. 

The only obvious difference (well don’t I think it was there before!) was the towbar symbol in the bottom left. 


It changed the view to this:


With the trailer electrics connected up it changed to this in normal view:

The parking sensors are disabled. 

I noticed the car fog lights don’t come on when testing the trailer lights. The trailer bulb check works well too, glad I don’t have LED bulbs!
I was wondering what else I got for all the efforts of going OE so asked my now good friend in the parts department what else the retro fit did to the car. He checked with someone who knew there & said they couldn’t cover everything, but essentially the whole car is effected from our active suspension to the brakes, 10 different systems were updated as part of the retro fit coding. 

If its really worth the huge amount of extra money & messing about over just getting a bespoke after market kit is questionable. The BMW coding cost alone is about the same a whole good aftermarket electrics kit! 

The service guy I was chatting to while waiting used to be down in the workshop, he said they’d had a few cars in where aftermarket trailer kits had gone wrong, because they connect into the CAN bus they cause huge damage to the car nowadays when they fail. Contrary to what any of the aftermarket kits may say they do invalid warranty claims if you have any kind of electrical problem.

Also not related to towbars, he said they have had lots of people who have messed up their cars trying to program themselves with Carly too. 

Before even getting the G31 I was chatting to my friend who runs warranty department at the same dealer, she said if they find you have anything but OE BMW electrics there’s no way they will be paying out. She also pointed out even if you’re outside your warranty they would always do their best to come to some kind of good will deal (obviously only if you hadn’t got aftermarket kit fitted). 

Of course the dealers only see the problems (bit like internet forums!) & never hear about all the people who are driving about never having had any issues….

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1 hour ago, 535i Andrew said:

Nice one Andy,  all you need now is the ability to charge the battery via pin 12!;)

Ha yes maybe one day, it would need a separate wire to pin 12, all the others go to sleep with the car. Same as your F10 I guess, hence you using 12….

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