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[Weds]

There's been numerous thread on fuse 15 blowing randomly, mine hasn't blown since driving in France in the summer. Today it blew on whilst on the M25, Brother in law driving at the time, had to give instructions over the phone whilst car was on the hard shoulder. Fortunately I have put a piece of PVC tape tab on the fuse and have quite a few spares in the glove box.

This is the first time its blown whilst driving at speed. Every other time its done it when stationary or nearly stopped.

Got car home and it blew another 3 fuses whilst parked up, but tried again a few hours later and its fine.

Checking in the handbook and it gives a list of items controlled by fuse 15, unfortunately they nearly all appear to be wrong.

Fuse 15 does NOT control the reverse lamps, seat and mirror adjustment, info display, control indicators or instrument illumination as listed in the handbook, They all still work with the fuse pulled.

I have not checked (yet) the level control (the relay is pulled anyway) the alarm system, cooling fan or headlight range adjustment. Its too dark at the moment.

Does anyone have a correct list of item connected with fuse 15 as the book appears to be wrong

[Kevin Wood]

I'll have a look at the wiring diagrams.

Kevin

[Kevin Wood]

OK, the following is what I think it powers on a 3.2:

Level control - feeds the compressor relay coil and ECU only.
Headlamp levelling ECU - switched feed
Anti theft / central locking ECU switched feed
Electric mirrors - feed to "parking position" relay (not fitted in UK?)
Front Seat heating - supply to the control unit, and possibly elements but not switches.
Reat seat heating - supply to switches, not control unit or elements
Mirror adjustment / seat adjustment - one of 3 supplies to memory seat, mirror ecu.
Headlamp switch - provides illumination only.
Manual transmission - reversing lamps.
Wipers - supply to rain sensor only.
Instrument panel - switched supply to instruments and many warning lamps.
MID/TID/GID/CID - switched supply.
Phone prewiring and telematics unit - switched supply.
Engine cooling - supply to air conditioning compressor relay coil, all engine cooling relay coils and test connector.

Kevin

[Weds]

Thanks Kevin

Gives me something to look for..

[Weds]

Been doing a few more checks this morning.

I've found that I can pull the fuse 15 with the engine running and it still carries on running, I loose the rev counter and the ignition light comes on, a couple of times the engine has just died with the fuse pulled, I suspect this is when the fault occurs.   

[Dave DND]

Weds, from following your problems for many months now, I must say that your intermittantly failing fuse sounds more like a trapped or chafing wire than a general failure of something.

Any work done to the car around the time it all started? Installations / service / accident ?

 :-/

[Kevin Wood]

Weds, from following your problems for many months now, I must say that your intermittantly failing fuse sounds more like a trapped or chafing wire than a general failure of something.

Any work done to the car around the time it all started? Installations / service / accident ?

 :-/

Agreed. Prime candidates in my opinion are the wiring to the Level control ECU, Headlamp levelling ECU, electric mirrors because these are exposed and / or prone to lots of flexing.

Failing that does it have a third party phone kit installed that might have botched wiring?

Thirdly have the failures coincided with the cooling fans starting perhaps? Could be a relay with a shorted coil winding.

However, if any work was carried out that might have affected one of these areas that's important to consider.

Kevin

[Weds]

Further update... Got my old laptop out and TIS

Started checking around plugs X1 and X3 as they come directly from the fuse.

It now blows a fuse as soon as the ignition is turned on..

In some ways this is good, I now have a permanent fault not a intermittent fault, much easier to fault find.

Just soldering up my 12v bulb to put in place of the fuse and start pulling some more plugs apart..

And yes chafed/trapped wire sounds a likely option..

Watch this space.. 

[Weds]

Spent a few hours checking through things. Still not found it, unfortunately the fault cleared and the car would run fine.

So far I've located and disconnected the level sensor underneath the back seat. This has a direct feed from F15, as the rear shocks and suspension have been changed to Bilstien the level sensor is not needed, the relay for the air compressor was pulled ages ago.

Found the rear seat heating relays are feed from F15 but it does not feed the elements. Also found 2 pence underneath the seat, and a lot of crumbs

Tried to find the headlamp levelling control, drawing shows it in engine bay near/underneath air filter, couldn't find it.

Have noticed, the front seats elements are fed from F15, they take around 8 amps each when switched on. Normal running with the seats off the current draw is about .5 amps (1 amp when the dash lights are first on) That explains why the fuse is 20 amps, it seemed a bit big for only a 1 amp load, till I switched on the front seat heating.

Tomorrow I'll have a further look around the front seat as there is a feed from F15 direct to them. not liking the air bags and seat tensioners around there though..

[Kevin Wood]

Sounds like you're on the right track. 

Can't recall ever having found the HL levelling ECU either. :-/

Sounds more like a wiring issue for me so areas where the wiring flexes (feeds into seats, onto doors, into mirrors, near suspension) have to be prime suspects.

Get a headlamp bulb in series with the fuse and give everything a waggle.

Kevin

[Weds]

Sounds like you're on the right track. 

Can't recall ever having found the HL levelling ECU either. :-/

Sounds more like a wiring issue for me so areas where the wiring flexes (feeds into seats, onto doors, into mirrors, near suspension) have to be prime suspects.

Get a headlamp bulb in series with the fuse and give everything a waggle.

Kevin

Thats what I've been trying.. Unfortunately now the fault appears to have cleared.  When it blows the fuse it seems to be just a pulse never on for any length of time

Question:- If I switch on the ignition with the dash out will it bring on the air bag light ? and will that be a Tech 2 to reset or can I use one of the cheapy code readers

Theres some checking to be done behind the dash

[Kevin Wood]

Yes, it will bring on the airbag light and it does require a tech2 to reset. :-/

Kevin

[Weds]

Yes, it will bring on the airbag light and it does require a tech2 to reset. :-/

Kevin

I'll probably disconnect the battery for that bit then.

Just a bit of a idea but when TB was putting in my CID some time ago, after we had put the dash back the fuse had blown.

From today I'll have the use of another car so I'm not tied down to fixing this asap. Which is good news as the inside of the car is littered with bits of trim and back seats. Just need to remember where it all comes from.