E39 problem starting and humming noise when switching off...

[sparks_E39]

My 528 is developing a problem it seems, battery is one year old. The battery light flickers very briefly sometimes whilst driving but doesn't stay on. It doesn't always start first time, nothing happens not even clicking when you turn the key, which is what happened when the old battery went flat. It starts after a couple of attempts no problems, doesn't even seem to struggle, but there is a 1 second long "humming" noise coming from it when it's switched off. Could it be the altinator? Any ideas? I do short 6 mile journeys to work every day.

[rtv]

Hi mate. It does taks a good 20 minutes of driving to put the charge back in the battery that you used to start it, so 6 mile hops to work and back won't be helping you at all. Needs to go out on a good run every now and then!

Failing that It's possible your alternator isn't charging the battery to it's full capability, or you might have some current drain in the system that is killing the battery when the engine is shut off.

Start the engine and switch on the headlights/radio/aircon etc, then stick a fluke on the jump start points under the bonnet and see what voltage it's showing, mine read 14.2v under the same test after i changed my battery recently.

Edited by rtv on Monday 14th March 12:07

Edited by rtv on Monday 14th March 12:08

[sparks_E39]

Thanks I'll do that, started first thing this morning covered in frost, but 9 hours later when it was considerably warmer it took 2-3 turns of the key, then started without struggling. The battery light flashed for 5ish seconds then all was well. Odd.

[sparks_E39]

Actually worked out today that if I keep the key turned 2-3 seconds more it starts first time, without struggling, it just fires up.

[sparks_E39]

Went to an indie yesterday. They could not find a fault. Altinator, battery and connections are fine. It seems every 4-5 times I start it it happens. Since its been to the garage yesterday, when it does it the battery light doesn't come on anymore, the abs, engine management and oil light comes on and it has struggled once or twice. Typing this into google, it seems some E39 owners have had similar symptoms with knackered fuel filters, although indie thinks its an electronical problem. Suffice to say, my indie is bloody good, and we are both stumped.

[sparks_E39]

Found the problem, faulty ignition switch! Car will be back on the road Tuesday all being well. Under £100 all in including diagnostics and a few hours of having it in bits from an indie.