Subject: That is very strange... I just repeated your test on my car with similar results Author: Brian (moderator) : member since January, 2005 : 8582 posts Posted on: 2009-01-14 12:53:05

Initially, I thought that your battery could still be the problem. According to one of Q's posts, a good, fully charged battery ought to register >12.6V. So, when I read that yours started at 12.3 and then dropped to 11.8 with the lights on, I thought that your battery might have an unusually high internal resistance and be on its way out.

So, I went out and repeated your test on my car. The electronics are enough different that a direct comparison between our cars is probably not relevant. My car has the later water cooled alternator and it has the dual batteries. However, the profile looked generally the same.

It is about 40 degrees out, and my car has been sitting since I drove it in to work this morning. I replaced my ignition switch last month, and my batteries are both only about 18 months old. I do not have any odd electrical symptoms. So theoretically, my electronics are close to ideal.

This is what I got...
11.5V Ignition switch in position 1, lights off
11.5V Ignition switch in position 1, lights on
11.1V Ignition switch in position 2, lights off
10.7V Ignition switch in position 2, lights on
13.8V Engine running, lights off
12.6V and rise back up to 13.6V Engine running, lights on

So, my car pretty much demonstrated the same battery behavior as yours. In fact, mine might even suggest that I have a bad battery.

Maybe you have a bad light control module or general module. The strange lighting symtpoms point to the LKM. On the other hand, the central locking and radio volume could point to the GM. It is an odd one.

Another possible component is the "Unloader Relay." That is located in the trunk, and it switches many of the electronics on. That can also cause some odd A/V symptoms, but I don't think it could cause the lighting symptoms.

After all this, I still suspect your battery. Is there any way that you could test another battery in your car? Do you have another car (or a friend's car) that could temporarily donate its battery to your car for the purposes of science?

• Calling Brian, KiwiJochen & all experts - one to baffle you? - e2djh 2009-01-11 07:30:41 (252 views)
  • Did you ever figured out this issue? - rex120 2009-04-10 03:30:22 (60 views)
  • Not Battery, not ignition switch, back to the drawing board!! - e2djh 2009-01-14 09:25:21 (155 views)
    • 14.5V does not sound right... (url) - Brian 2009-01-14 11:22:30 (164 views)
      • ooops - results - e2djh 2009-01-14 11:38:02 (139 views)
        • That is very strange... I just repeated your test on my car with similar results (url) - Brian 2009-01-14 12:53:05 (151 views)
          • Battery Swap - e2djh 2009-01-14 14:52:05 (114 views)
            • Your wife's E39 battery is a 100% compatible perfect swap... - Brian 2009-01-14 16:46:24 (122 views)
              • The battery is fine is there a test for LKM or GM? - e2djh 2009-01-16 15:27:57 (125 views)
                • Dealer or somebody with a DIS can test the modules directly. (nt) - bmw635 2009-01-18 00:24:44 (114 views)
                  • Thanks. Is DIS software available to download, or is a dealer needed? (nt) - e2djh 2009-01-18 05:06:11 (114 views)
                    • Check on BMWECU.org. (nt) - bmw635 2009-01-20 00:26:21 (109 views)
              • I'll give that a try - e2djh 2009-01-14 17:01:43 (117 views)
          • Rr: That is very strange... I just repeated your test on my car with similar results (nt) - e2djh 2009-01-14 13:29:41 (108 views)
      • sussed it - test 9. results (nt) - e2djh 2009-01-14 11:30:53 (122 views)
      • am in car now, no test 39, only goes up to 21 (nt) - e2djh 2009-01-14 11:28:36 (107 views)
  • Igntion switch is faulty (url) - kiwijochen 2009-01-12 14:55:54 (161 views)
    • Battery, KLR relay or ignition switch would be my best guess (nt) - Martin 2009-01-15 18:54:52 (107 views)
    • Igntion switch has now been replaced - didn't do the job - e2djh 2009-01-14 16:17:34 (126 views)
    • Re: Igntion switch is faulty - e2djh 2009-01-12 15:00:56 (125 views)
      • NavCoder *might* show corrupt messages - kiwijochen 2009-01-12 16:30:32 (135 views)
        • Will do, i will be ordering it tomorrow. - e2djh 2009-01-12 16:32:40 (118 views)
          • Look for the black dot on the battery... - Brian 2009-01-13 11:16:25 (106 views)
            • Battery is dated 2006... but black dot (nt) - e2djh 2009-01-13 11:26:15 (109 views)
              • If you have a black dot, the battery is undercharged - Brian 2009-01-13 11:44:57 (116 views)
                • Thats interesting Brian, I saw that written on the battery, but - e2djh 2009-01-13 12:47:14 (115 views)
                  • You have to look at it straight down from the top... - Brian 2009-01-13 13:22:15 (124 views)
                    • Thanks, had to take it out, but its ok - see above (nt) - e2djh 2009-01-14 11:22:18 (104 views)
  • Here are a few thoughts... - Brian 2009-01-12 08:37:44 (149 views)
    • You were right about the radio Brian - e2djh 2009-01-25 06:00:56 (107 views)
      • Wow, it is great to see progress... - Brian 2009-01-25 08:32:04 (110 views)
        • Yes, progress is slow ... - e2djh 2009-01-25 08:49:13 (114 views)
          • I agree: E38 radio R&R is a beast - Brian 2009-01-25 16:01:31 (106 views)
            • 'new' map DVD on its way + new info on lights - e2djh 2009-01-25 16:43:11 (100 views)
    • Very helpful input Brian thanks, some feedback: - e2djh 2009-01-12 14:56:30 (123 views)
      • Are you anywhere near Glasgow? (nt) - ksmith38a 2009-01-17 13:45:17 (113 views)
        • No, i'm in Berkshire, why do you ask? (nt) - e2djh 2009-01-17 16:49:58 (106 views)
          • Thought if you were closer I may have been able to help (nt) - ksmith38a 2009-01-18 05:09:33 (111 views)
            • That's kind of you, thank you. Its a bit of a long haul to Glasgow :-) (nt) - e2djh 2009-01-18 06:53:39 (105 views)
  • Anyone? Help required please! (nt) - e2djh 2009-01-12 02:07:51 (127 views)
    • Going back a few steps - ksmith38a 2009-01-18 10:55:17 (106 views)
      • Mostly, yes - e2djh 2009-01-18 11:12:22 (92 views)
        • Re: Mostly, yes - ksmith38a 2009-01-18 11:20:09 (109 views)
          • One was totally shot. - e2djh 2009-01-18 12:01:48 (92 views)
            • My thoughts, swap them one at a time and see what happens - ksmith38a 2009-01-18 12:25:13 (113 views)
              • That's what i thought - e2djh 2009-01-18 15:58:49 (100 views)