W220 S500 blowing 15A fuse, faulty central locking/command!

[MrDave123]

Hi guys,

I’m really struggling with an electrical issue on my ’99 W220 S500. The central locking isn’t working, nor is the command unit. Its blowing the 15A fuse (pictured) under the rear seat compartment. It’s a proper short too as it turns the fuse into a lightbulb within ¼ a second of replacing.



Everything else seems fine. Soft close doors, rear head rests, boot release, locking/unlocking from the button on the dash and locking itself when driving. I can’t find any other systems that aren’t working apart from the central locking from the keyfob (the light flashes on the key) and that the command is dead.

I’ve unplugged the alarm sounder in the passenger wheel arch, plus taken out the command unit but the fuse still turns into a lightbulb instantly.

I’m not sure where else to look. Any help would be much appreciated!


Cheers,
Dave

 

[Uky]

I once owned a CL500, "C215". The same technical platform.

The soft-close is vacuum controlled. Same thing with the rear head-rests. No relays or actuators there.

That car developed a problem with the cable harness between the body and the door mechanisms. (The CL has special hinges that enables the driver and passenger to get out of the car when parked in a cramep parking lot but this does not apply to the W220) . The cable harness in my car was fabricated using very stiff cables with few strands and over the years, the copper was bent forward an backward and the insulation was gradually destroyed. Eventually, short citcuits developed. I was able to fix it myself but that included repairing some cable that are used by the SRS. (Airbags in the CL Doors). Be careful.

There should be sensors in the doors that should indicate wether the doors are open or shut. If these sensors fail to respond, I would suspect a cable fault.

Another thing to look for is the boot lid. The cable between the body and the lid can also get torned and there are +12V routed to the license plate illumination

We have no ferrets where I live that eats cable harnesses like they do in continental europe and if this is a problem in the UK I do not know but eaten cable harnesses is a big problem.

I suggest that you have a look in the fuse table on which systems this particular fuse protects and then start from there.

 

[wrdcc01]

Wish I still had 220 wiring diagrams. This is odd since you've identified correctly all the other circuits running through fuse 62 and the locking working without the remote. The rear SAM controls the remote receiver system so the problem is likely there. Don't suppose you have a spare one to hand? Any damp on the floor?

 

[Flyinspanner]

Look in the boot.
Nearside (left) remove trim panels, the PSE pump is mounted there, and (lower down) the CD player and Amp.
water can get in from boot seal, the pse pump gets wet and fails. It is housed in foam which can hold water.
it then flows down and can blow the Amp.

Taking out CD & Amp is easy and you can check for moisture/ clean out the well it sits in. The amp does have a blade fuse in it as well.

I did once have to change my amp, it was the Bose version, tricky to find - so I bought one from a CLK similar age, fitted perfectly - though I did have to cut a plastic keyway off the socket with a scalpel to get plug in. (Think maybe plugs had just slightly changed by year - but not the pins)

 

[MrDave123]

Hi guys,

Thanks for the replys so far! Water.. well I have had a leak coming in down the drivers A-pillar and onto the floor. A bit did get into the drivers door (it was parked on an angle in a monsoon!) and the wing mirror motor started driving about on its own maybe 6 weeks ago. Once it had dried out, I plugged in my MBII code reader and reset a load of short circuit faults related to the door. All that stuff has worked fine since mind. I had sort of ruled that out in my mind though because none of the affected systems seem to be related to any of the door modules?

I've just popped up the rear seat and its dry as a bone under there, no signs of damp ever as far as I can see.

When I acquired the car it was missing the CD changer, so there's nothing at all in the boot space on the rear left. When I had the Command unit out, I checked both of the fuses on the back of that, neither had blown.

I don't have any wiring diagrams, but is is possible that the water in the door issue has damaged the rear SAM and its now blowing the fuse? It does seem strange that all of the PSE related stuff is still working as I thought that having that fuse blown would have disabled all that stuff?

My other thought is that the alarm sounder's battery is likely to have gone bad, being 20+ years old and could have shorted something out, damaging the SAM?

I don't have a spare SAM, but see there are some on eBay. Are these things all the same does anyone know? Mines a reasonably basic S500 with just optioned wooden steering wheel and extra helpings of rust!



Dave

 

[Flyinspanner]

If the CD player is missing you won’t get any sound. It’s on an optical ring, so no signal will go to the head unit from amp. All components have to be in place.
The head unit should light up you just won’t get sound.

If there Is nothing in the well on left side of boot, you are missing the amp as well. You then wonder why... are any of the wires touching body (short) or damaged.

see if the pse pump is in place, is foam dry, are any of the pipes off it? Can you hear it run? Is there 12v at pump?

 

[MrDave123]

If the CD player is missing you won’t get any sound. It’s on an optical ring, so no signal will go to the head unit from amp. All components have to be in place.
The head unit should light up you just won’t get sound.

If there Is nothing in the well on left side of boot, you are missing the amp as well. You then wonder why... are any of the wires touching body (short) or damaged.

see if the pse pump is in place, is foam dry, are any of the pipes off it? Can you hear it run? Is there 12v at pump?

Hi Flyinspanner,

The missing CD player is unrelated, I just mentioned it as someone thought it may be wet. The command has always worked fine without it as a standalone unit - it doesn't have the external amp/BOSE. Nothing is shorting out

PSE system is all fine, pump runs as it should and everything PSE related works. I've had issues with the PSE in the past and have rebuilt the pump (had the car 10+ years!) and am 99% sure its nothing to do with the PSE, even though the fuse thats blowing does seem to be for the pump on other cars?

 

[MrDave123]

A small update. I've pulled out the drivers door module that was wet a few weeks ago and thought I had it.

Popped in another replacement fuse, central locking worked from the fob, radio came on then after 1 min I heard a POP and the fuse went again. Each subsequent fuse blew immediately. Must have been a strong fuse that one... It did spark a little as I plugged it in. So, its not the door module that got wet the other month, and everything did actually work for a short time. Just something on that fuse pulling a lot of power.


I'm struggling to find a fuse chart or any wiring diagram that matches my car. All the ones I find tell me that the fuse thats blowing would also take out the PSE system, but all that stuff is fine. Or they show the command/radio on F61, but its on the same fuse as remote locking on my car. I've spent a bit of time trying everything else out and I'm just missing locking/unlocking from the fob and the command/radio. The diagrams all show a 20A fuse in that position too instead of a 15A. I guess someone could have put the wrong one in there in the past, but its not one I've changed in the last few years thats for sure.

 

[oldguy57]

A small update. I've pulled out the drivers door module that was wet a few weeks ago and thought I had it.

Popped in another replacement fuse, central locking worked from the fob, radio came on then after 1 min I heard a POP and the fuse went again. Each subsequent fuse blew immediately. Must have been a strong fuse that one... It did spark a little as I plugged it in. So, its not the door module that got wet the other month, and everything did actually work for a short time. Just something on that fuse pulling a lot of power.


I'm struggling to find a fuse chart or any wiring diagram that matches my car. All the ones I find tell me that the fuse thats blowing would also take out the PSE system, but all that stuff is fine. Or they show the command/radio on F61, but its on the same fuse as remote locking on my car. I've spent a bit of time trying everything else out and I'm just missing locking/unlocking from the fob and the command/radio. The diagrams all show a 20A fuse in that position too instead of a 15A. I guess someone could have put the wrong one in there in the past, but its not one I've changed in the last few years thats for sure.

I would have a look at the website Fuse Box info. Much more detailed than the info MB include on their fuse sheets.

 

[MrDave123]

I would have a look at the website Fuse Box info. Much more detailed than the info MB include on their fuse sheets.

I've just found that as it happens, many thanks! I think the top one on the below pic is me (2000 car), but it doesn't mention the central locking. I don't have the TV tuner or CD. I did swap out relay 15 too just in case..

View attachment 109943

Circuit 15, is that the CAN bus? I think there's a CAN bus distributor block under the drivers seat? I wonder if that got wet and could be causing my problems?

Bit cold and getting dark outside. I'll have another look tomorrow.

Thanks once again forum people!

 

[MrDave123]

The plot thickens (a little bit!).

I thought the battery was on the way out on this thing as it would run flat if not used for 5-7 days. That issue has now gone and it spins over the motor super fast each morning with this fuse blown. Clearly there's been a drain going through the fuse for some time and its just got worse, now blowing the 15A fuse.

It is fuse F61 thats blowing (removed in this pic, green holder red/yellow cables).



My fuse chart shows F61 as:

CD Changer (I don't have one)
Radio/Command (its on the bench next to me, fuse still blows)
Navigation system

The fuse chart also says the fuse F62 is for the central locking, so presumably thats why thats still working from the button in the car and auto locks when driving.

Clearly F61 also does the keyfob remote receiver also.

So, I just went looking for the remote receiver in the boot and found the following tucked up behind the carpet near the PSE pump:



Success!!!!!!!!! Such a relief as I was about to throw in the towel! Chopped off the connector, terminated and no more blowing fuses, everything working again! Looks like it was power for something audio related in the boot and has the same red/yellow cable.

Thanks for all your help forum people! Flyingspanner - you were right all along!

 

[herveybaymb]

That plug appears to be the 3 wire power supply to a 6 CD stacker that mounts in the left lower rear of the boot and can get very et if the rear light fitting leaks! Fuse 61 is the fuse for this CD player as you have found out.