#4 fuse keeps blowing.

Specific conversations and info for the BMW E28 M5 and M535i.
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M5ZEALOT
Posts: 1271
Joined: Aug 14, 2007 11:09 PM
Location: San Diego, CA

#4 fuse keeps blowing.

Post by M5ZEALOT »

Hi Guys,

Rushing to get the M5 ready for Bimmerfest this weekend but my #4 fuse blowing issue has finally reared it's ugly head. It's been making detailing difficult since I can't adjust the seats now. Some history: for about 4 years the fuse will blow at least once every six months if I turn on both seat heaters on. Sometimes it was fine w/ both heaters on. I never really did more troubleshooting since it happened so infrequently.

I have disconnected; seat heater switches, seat adjustment switches and lighter. ( Power antenna wire has been disconnected and disabled for 15 years now) The fuse blows w/ ignition off and all these switches disconnected. I'm not very good at tracing shorts so will have to do more studying. Got a new multimeter and ready for any suggestions or words of wisdom.

Oh yes, I have checked all my after market alarm and audio system wiring. No faults that I could attribute to blowing fuse. Thanks :oops:
mooseheadm5
Beamter
Beamter
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Location: Charlottesville, VA
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Post by mooseheadm5 »

Fuse 4 does SLS, driver's seat controller, driver and passenger thigh bolsters, power antenna, and the lighter. You could try a temporary resetting fuse from an auto parts store whilst you wiggle stuff to see what is up. I would check the cigar lighter, and you can also completely unplug the seat power switches and thigh bolster switches.
M5ZEALOT
Posts: 1271
Joined: Aug 14, 2007 11:09 PM
Location: San Diego, CA

Post by M5ZEALOT »

mooseheadm5 wrote:Fuse 4 does SLS, driver's seat controller, driver and passenger thigh bolsters, power antenna, and the lighter. You could try a temporary resetting fuse from an auto parts store whilst you wiggle stuff to see what is up. I would check the cigar lighter, and you can also completely unplug the seat power switches and thigh bolster switches.
Oh wow, didn't know it controlled SLS. I disconnected that system a few years ago. I'll check what's left of the wiring and see if I find anything. The reset tool will be great so I don't waste anymore fuses. Did I mention every fuse I put on blows regardless of what's on or off. :shock:
mooseheadm5
Beamter
Beamter
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Post by mooseheadm5 »

That is called a dead short. Finding a dead short is easier. Put a multimeter on continuity check and hook it between the fuse box (not the power side, the side that runs to the seats, etc with no fuse installed) and hook the other end to ground. It should beep or show 0 ohms or close to it. Unplug stuff till it stops beeping or shows a significant resistance. That is where the short is.
M5ZEALOT
Posts: 1271
Joined: Aug 14, 2007 11:09 PM
Location: San Diego, CA

Post by M5ZEALOT »

mooseheadm5 wrote:That is called a dead short. Finding a dead short is easier. Put a multimeter on continuity check and hook it between the fuse box (not the power side, the side that runs to the seats, etc with no fuse installed) and hook the other end to ground. It should beep or show 0 ohms or close to it. Unplug stuff till it stops beeping or shows a significant resistance. That is where the short is.
Excellent! Thanks so much for your help! Battling a bad cold but hopefully have this bug (and electrical one) fixed by this weekend! :banana:
Low_N_Slow
Posts: 9
Joined: Mar 17, 2016 12:34 AM
Location: sacramento

Re: #4 fuse keeps blowing.

Post by Low_N_Slow »

Did you end up find the problem? Im having the same issue
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