is my 97 M3 dying? (radio, a/c, brake lights, dash LEDs... problems)

leobag · 07-23-2005, 11:17 PM

This forum has more action vs. the M3 forum, so I figured I would post here. I have always heard that BMWs have electrical problems... however, my car was doing so well up until about a 1/2 year or so ago.

I got my 97 M3 new, so I know all the history. The first electrical issue I noticed was the "Brake Light Circuit." The OBC reported a failure in it. By replacing the burnt bulbs, I was able to get rid of that error - unfortunately it has come back someone quickly (about a couple months later). Now the OBC either reports the same "Brake Light Circuit" error, or will just tell me something like "Brake Light Failure." I forgot the exact message, however, it is very similar to the "circuit" error.

Also, I notice the following problem coming in and out... the LEDs behind my speedometer seem to fail - but then come back to life. Usually it is only the LED behind about 80 MPH... some times it is more than one, but usually just one. The weird part is that it will come back to life... then a couple weeks later, it will die, etc...

A little after that, my radio decided to stop working. This is the biggest bummer of all. No tunes is *hurting.* The back light for all the buttons are still functional, but all the buttons are dead. It started out with a dim display (when the radio was working)... the LCD display started getting noticeably dim. Then, the radio/CD just stopped working. The very, very strange part about this, is that every once in a while (NOT often), the radio will come back to life and ask for the code to operate. I enter in my code and my music comes back! Typically this only lasts for the driving session. Next time I get in, start the car, nothing... a dead radio.

The latest episode of this drama has to do with the air conditioner and heater system. Dead. The buttons just don't do anything... very similar to the radio issue. Again similar to the radio issue, the system decides to work every once in a while. This is more frequent than the radio, but still it is not dependable, and is seemingly happening less and less. One thing about the Air system... when it DOES decide to come on it will turn off and on randomly like a power connector somewhere is touching and going or something like that.

OK, so... those are my issues. I am hoping it is something as easy as a few dead fuses - but would a fuse act like this?? I wouldn't think so... the random working/not_working issues lead me away from fuse related problems. I am not a lazy guy, but I haven't even checked the fuse area... so I should probably do that - but in the mean time: do you guys have ANY suggestions?

Thanks a lot,
Leo

BMWCowboy · 07-24-2005, 06:19 AM

You need a brake light switch for the brake problem, and couple of bulbs in Inst cluster-->as far as the radio goes....maybe pull it out (very easy) and make sure nothings come loose....and for the A/C sounds like you need a new control unit....you can replace a resistor in it that also fixes this problem

Wayne 962 · Wayne 962's Garage

Believe it or not, many of these problems can be caused by faulty trunk wiring - it's the first place I look when I hear something like this. Here's a photo of the bad wiring I found in my E36:

-Wayne

leobag · 07-25-2005, 07:27 AM

Oh wow Wayne that's crazy... it was just like that when you found it? Where should I look for something like that (what part of the trunk)?

Thanks,
Leo

blkongry · 07-25-2005, 02:38 PM

As for the brake circuit, I'd do like Cowboy said and check that brake switch. You should also check your contacts where your bulbs sit in the rear... it could be corrosion. Just make sure they are clean and making good contact. I believe the circuit is resistance sensitve, and when it senses a high resistance area, it trips the fault light. Should be a pretty easy fix.

I'd also check the wiring like Wayne says, but if you are the original owner, you are probably good. A lot of stuff like what he showed is due to someone getting their grubbies in there and messing with it before you got the car, or it was in an accident and they 'modified' something when they repaired it.

I'd also check the connections on the radio (I feel ya on the no tunes... that's tough). It could be a bad connection, or it could be an electrical component that is dying. Some take a while to actually die, so they can temporarily revive... it's usually contact related. If it doesn't come back, then it's a good reason to upgrade (not a big fan of the factory systems).

I'd also agree on the control system. Either replace the resistor and see if that remedies things, or get a replacement unit (can probably find a good one on Ebay).

I've never heard these cars were problematic with electrical issues. Mine has been flawless and the wiring is clean and nicely done. I'm impressed with it. It's not like my old girlfriend's Fiat Spider... phew... I ran laps chasing down electrical problems with that car.

frankc · 07-25-2005, 07:18 PM

My bet would be the rear trunk harness, like Wayne said, as it is a definite weakness in the E36. BMW sells a repair harness for this very reason.

Hopefully I am not violating any forum rules by posting this, but here is a link that describes the problem (and solution) in detail:

http://forums.bimmerforums.com/forum/showthread.php?t=79896

The part number for the trunk repair harness is 61 12 8 391 788. The price is about $80. You should verify that number for your car. I'm sure our host can get it for you.

Here is a link: http://www.realoem.com/bmw/showparts.do?model=CD93&mospid=47504&prod=19980300&btnr=61_0105&hg=61&fg=10

Wayne 962 · Wayne 962's Garage

No need to buy a new harness - just resolder the wires, and you should be fine. The harness is on the left side of the trunk...

-Wayne

leobag · 07-25-2005, 10:07 PM

Wow, you guys have been more that awesome. I really appreciate all of the suggestions and will let you guys know how things go. As far as "contact" issues... what should i be looking for? I am a total n00b when it comes to cars

For example... where is the brake light switch?

Again, you guys are awesome... thanks for the help,
Leo

blkongry · 07-25-2005, 10:15 PM

Man... read through that link... what a nasty failure... almost caused a car fire, eh? I can see that happening. That'd be horrible to be an engineer and find your design has an inherit flaw like that.

blkongry · 07-25-2005, 10:19 PM

Brake light switch is under the pedal. There's a pic somewhere here on the web... you can probably find it with a Google search.

I'd go after that frayed trunk harness issue. Man, there were a lot of them on that link. I'd check mine, but my last girlfriend got rear ended in mine (lightly), and they replaced the trunk lid, so I think I'm good.

leobag · 07-31-2005, 11:32 AM

Hi guys,

Good news, my rear wire harness looks to be fine, I read through that crazy thread... heard about fires and electrical wire damage all the way through to under the driver's seat... very scary - I can't believe BMW hasn't done something about this (recall or whatever).

Now I am going to fix the "Brake Light Circuit" issue. One thing that I want to verify, is that the "Brake Light Circuit" issue is related to the brake like Switch - right?

In the great article on this site, it says "It's important to note that the BMW warning system that tells you when a lamp is out will not tell you if the switch is broken - you will have to figure it out for yourself." But doesn't the "circuit" warning tell you that switch is malfunctioning? Or are these two things not related?

Thanks,
Leo

BMWCowboy · 11:48 AM

You need a brake light switch for the brake problem, and couple of bulbs in Inst cluster-->as far as the radio goes....maybe pull it out (very easy) and make sure nothings come loose....and for the A/C sounds like you need a new control unit....you can replace a resistor in it that also fixes this problem

hmmmm seeeems like i said this before

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by leobag
Hi guys,

Good news, my rear wire harness looks to be fine, I read through that crazy thread... heard about fires and electrical wire damage all the way through to under the driver's seat... very scary - I can't believe BMW hasn't done something about this (recall or whatever).

Now I am going to fix the "Brake Light Circuit" issue. One thing that I want to verify, is that the "Brake Light Circuit" issue is related to the brake like Switch - right?

In the great article on this site, it says "It's important to note that the BMW warning system that tells you when a lamp is out will not tell you if the switch is broken - you will have to figure it out for yourself." But doesn't the "circuit" warning tell you that switch is malfunctioning? Or are these two things not related?

Thanks,
Leo

That's correct, In my article, it says that your BMW will tell you when your light is out, but not when the switch is not working (it just thinks you never press your brake pedal)...

-Wayne

BMWCowboy · 07-31-2005, 12:53 PM

Thats NOT correct->>It will either say brake light BULB or brake light CIRCUIT->>circuit is the switch...bad socket will say bulb or a bad taillight will also say bulb

leobag · 07-31-2005, 01:04 PM

Quote:

hmmmm seeeems like i said this before

Cowboy, I just thought i would update the thread... maybe it would help people - maybe not. Also, I think I had a legitimate question to ask. Sorry if I inconvenienced you with reading my post.

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by BMWCowboy
Thats NOT correct->>It will either say brake light BULB or brake light CIRCUIT->>circuit is the switch...bad socket will say bulb or a bad taillight will also say bulb

On my 1992 E36 it did not indicate the faulty switch - my wife had to tell me that my brake lights were not working.

Maybe in some cases where the switch fails closed it will tell you, but when it fails open, it doesn't appear to indicate a failure? Don't know. Perhaps the later cars have this feature, but not hte early ones?

-Wayne

BMWCowboy · 07-31-2005, 01:33 PM

Sorry Leo>>just trying to help fix ur problem without tearing anything else up >>but you go on with ur badself

blkongry · 07-31-2005, 01:48 PM

If it's not the frayed wiring harness, then I'd go after the brake light switch next, like Cowboy said. I know they are problematic, and if all your lights are working, then it's probably your problem. If that doesn't do it, then check your connections for corrosion and change out bulbs, but I think the switch should get you running right.

Either way, let us know.

BTW, pics like what you posted are incredibly helpful for everyone. Wayne, you do a great job with definitive pics, too. Thanks!!

Wayne 962 · Wayne 962's Garage

FYI, everyone should check their rear trunk harness - I have three cars with 2 frayed harnesses.

-Wayne

leobag · 08-04-2005, 09:51 AM

Update:

I switched out the brake switch and burnt bulbs - that problem is solved. On the radio issue... I removed the radio and everything looks fine. I don't really know what to look for, but nothing looked damaged to the rear of the unit and all wires and fuses look fine.

The issue is that the head unit no longer functions. The keys illuminate but the power button does nothing. It used to spring back to life ever once in a while (asking for the CODE), but it has not done that for a while now. I have the BMW CD changer hooked up - I don't know if that might cause issue.

Anyone with tips on what to test/look for?

Thanks.