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Old 09-15-2011, 11:01 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 19,181
Mein Auto: 02 BMW 525i M54 automatic
Case study: Low-voltage dead instrument cluster - no alphanumerics & most gauges inop

I haven't done the research yet to figure out what could possibly be happening; so allow me to simply report what happened today to my 2002 525i instrument cluster & MID:

SUMMARY:
  • DEAD:
    • All alphanumerics on the instrument cluster do not display
    • Clock on MID does not display
    • Fuel gauge is dead (see intermittent anomaly below)
    • Tachometer is dead
    • High beam blue display is dead
    • Almost all warning symbols appear to be dead (see exceptions below)
  • ALIVE:
    • MID display works for radio/CD/mode functions only
    • Speedometer needle works
    • Temperature gauge needle works
    • Manifold vacuum (i.e., fuel economy) gauge needle works
    • Green turn signal display & hazard light display both work
    • Back lighting works when I turn on the headlights
    • On the left side of the cluster, the red battery & red low oil level indicators work when turning key to position 1
    • On the right side of the cluster, two lights go on when I start the car (I don't remember which so I will snap a picture later of them)
  • INTERMITTENT:
    • The fuel gauge (which is at 3/4 tank) started working 15 miles into a 20-mile drive; but upon restarting the car for the 20 mile return drive, it stayed dead.
DETAILS:
  1. Cluster & MID displays were working fine.
  2. At home, I forgot to enter the mileage into my mileage log, so, I went back to the car for that data, and accidentally left the key in the ignition with the ignition on but the car not running (I don't remember if it was position one or two but certainly not three).
  3. Only a couple of hours later, I tried to start the car but it was completely dead (which is surprising after just a couple of hours since the headlights were not on).
  4. No indications of alternator/battery or FSU problems (but of course, I will check that in the debugging stage); battery is about five years old (will check voltage at the terminals).
  5. With the ignition key off, I put my 4-amp battery charger on the correct engine points and was surprised to see the amp meter needle pegged way past the 6-amp point.
    • I didn't snap a picture as I figured the battery, somehow, was just overly depleted and that it would go down to 4 amps soon.
  6. I left the charger on for about an hour, maybe two hours
  7. Upon starting the car, I tried to unlock the cluster to check alternator output, but was immediately startled by the lack of ANY alphanumeric display!
At this point, I've done zero research ... so I have to figure out how the cluster works in order to figure out WHY those particular items are dead and alive.

But, as always, pointers are welcome at this early stage in the debugging process!

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Last edited by bluebee; 09-20-2011 at 09:59 AM. Reason: Changed the title, once the solution was known, so that others searching titles might find this help more easily.
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