Weird Electrical issue - Anyone seen this behavior?

[madjeff]

OK, I have a weird issue with my E34 that I'm just now starting to track down, but thought I would post and see if anyone has seen this type of thing before.

'92 525i M50/AT 177k miles

Not long after I bought it in September I noticed that occasionally the interior map and side lights would flicker on and off (when set to auto) while I was driving, like the door was not quite closed. I figured I had a door switch going bad or a short somewhere and just set the light switch to the off position until I had a chance to dig into it deeper. Now I notice that when I switch the dome lights back to the auto setting, they will not light when any of the doors are open. However, they will light when I set the switch to the On position, so I have good bulbs.

Around the same time, I noticed that I would occasionally get a "Brake LT Circuit" message kick on as well, maybe once a week or so. I checked all the lights and everything seems to be working great, no bulbs burned out or anything. Sometimes I go for weeks without a message, then I'll get 3 in two days. After stopping the car and starting, the error message is gone. Again, one of those irritating things that I was planning on getting to soon.


So, after driving it for a month or so I left the car sitting for a couple days without driving, and ended up with a dead battery. Figuring it was probably an old battery (and spending an hour trying to figure out where the damn thing was located, stupid newbie Bimmer owner... ) I pulled the rear seat, only to find the battery was almost new and of good quality. I charged it, and all was well for a week or so, until I let it set again for 2 days, then same thing, dead batt.

So, I obviously have a short somewhere. The alternator seems to be charging ok, as once the car is started it will charge the battery right up to full charge. I have not yet had a chance to pull the negative cable and put a meter to it to see how many amps the short is pulling, but I have pulled the dome lights fuse and it still runs down. I'm starting to wonder if these issues are all connected, or if it's just a coincidence.

I'm going to jump in this week and start trying to narrow down the issue, but am hoping someone has had this same issue before and can point me in the right direction. Yes, I'm lazy. I do have the Bentley manual as well as a huge wiring doc I pulled from another thread, and have started trying to trace the connections, but of course they don't actually tell you WHERE in the car the connections run, so I'm going to have to do some tracing.

[632 Regal]

your on the right track with pulling fuses and relays. The alternator could have bad diodes draining the battery as it sits but I wouldt go there yet. Hook up the ampmeter and pull fuses 1 at a time til you find the drain.

[Ross]

The dome light switch is bad. Check also the brake light switch, do a search, it seems common.

[madjeff]

The dome light switch is bad. Check also the brake light switch, do a search, it seems common.

I'm assuming you mean the overhead switch on the dome light itself? Since the fuse was pulled and the battery still died, I wouldn't think that was the problem, but I'll check the switch for wear/issues.

[Spasso]

Here are some of the neat messages I've been getting,

I've owned my 328iS for 1,000 miles and had some interesting things start happening recently. To start with, I did an oil change and transmission service as well as replaced the cooling system.

1. I pulled on to the freeway under moderate acceleration to 70 MPH. Five miles down the road I get the transmission warning light, (exclamation inside the gear insignia). This is occuring at normal cruise. I shifted the trans back and forth and found no problems or slipping.

2. Right after the trans light came on the ASC light flashed on (exclamation in triangle). I hit the ASC button a few times but the lights stayed on steady so I pulled over, read the owners manual. Shut off the engine in hopes of resetting the lights. It didn't work.

3. After 30 miles the check engine light came on in addition to the other two lights. Mind you, the engine is full of oil and water. It's running great!, shifting great and I am getting 24/25 MPG city-highway driving!

I reached my destination and shut it off. After I came out an hour later ALL of the lights were OFF. I thought, "weird".

4. The the next day while driving, the OBC annuciated "Brake circuit fault". I check the bulbs and the two main bulbs were out but the 3rd eye was still working. I replaced the bulbs and all seemed fine for about half a day. I got the "brake fault" message again as I was backing into my garage even though all three brake lights were working!! WTF??!!

Before I go any further on this I decided to buy a Peak OBDII to alleviate the guessing game.(NO STOMP TEST ON THIS CAR). Got the Peake Tool and the only codes I get are "idle sensor fault" "Improbable idle parameters"

I thought I would throw this out there to see if anyone has had similar events.

Could it be a problem with the the ECU?? OBC??

1998 328is, A4S 270/310R automatic. Build date 1/98

Currently;

I get the brake fault message everytime I drive the car Brake light switch? even though the lights all work BUT
No "Check Engine Light"
No "Trans Warning Light"
No "ASC Warning light"

Any patterns here??
AHHHH, The wonderful world of electronics.

[Ross]

I missed the part about pulling the fuse for the dome light. The occasional coming on at random is what brought me to that conclusion. Perhaps still worth a look though.

[Ross]

There is also an inertia switch on the wiring diagram. Apparently in a crash the interior lights will illuminate. Those Germans, they think of everything.Perhaps this is sending an erroneous signal.

[Spasso]

There is also an inertia switch on the wiring diagram. Apparently in a crash the interior lights will illuminate. Those Germans, they think of everything.Perhaps this is sending an erroneous signal.

The doors automatically unlock and the fuel pumps shut off as well.

[madjeff]

Ok, Update time. =)

I pulled the negative cable off the battery, hooked the meter inline and set it to the 10amp setting. with everything off I'm getting a .15 amp draw.

I then had my wife watch the meter while I started pulling fuses. I started with the front fuse box and pulled every fuse and relay in that box, and never got anything less than .15 amps. I switched to the back fuse box and pulled everything on it, same story.

So, first off, is .15 amps seem a little high for a car at rest, or is that OK? Am I missing any fuses? I pulled everything including the LKM and 12v Check Control modules from the front box, however I only pulled the fuses and 2 yellow relays from the back box, as I could not seem to be able to get the cover off the back box, it acted like there was one screw left, but I couldn't see it anywhere.

The battery after driving today is a solid 12.6 volts. I'm going to leave the battery unplugged for the night and test it again in the morning to see where it's at. But right now I feel like I've made zero progress...

[madjeff]

Well, checked the battery voltage this morning and it was at 12.5, so it looks like the battery itself is holding a charge. So, what's my next step here?

I'm still a little unclear as to what the normal amp draw is supposed to be. Looking at the Bentley manual, it states that 500 milliamps (0.5amp) draw or more indicates a problem, but I seem to be well under that at .15 amps.

Any helpful hints on what to check next?