Halp! I Haz E46 Weirdness!

I have an intermittent problem on my '01 330ci while running. Suddenly the audio goes silent for about 1.543 seconds, the traction control, ABS, and air bag lights come on the dash, and if the cruise control light is on, it turns off. And if the headlights are on they dim. Then the lights go off, the audio comes back on and the cruise light stays off. At first this was happening very infrequently, but has slowly started to happen more often. I most often happens when starting up from a stop, but also happens when just cruising down the road. I'm hoping this is a known problem. I'd appreciate any suggestions beyond the basics.

Conventional E46 wisdom says that step 1 for any electrical weirdness: get a brand new battery. Make sure you connect a battery charger to the leads while you hot swap it.

I haven't had to do it yet, but that's just what 'they' say over at E46fanatics.

Check your grounds. Number one cause of electrical wierdness is a loose or corroded ground contact.

Never heard of it, but I agree with Tyler a new battery solves many an electrical problem on these cars.

I would check grounds, check batter and then check the alternator last.

Battery.

When they start to go the car is operating on a lower voltage (despite a healthy charging system) and lots of 12v solid state electronics start turning on/off at around the 10v mark. So, steady state loads operate near their threshold, then intermittent ones like seat motors, wipers, AC actuators... etc pull it a hair lower and transistor switching hilarity ensues. On the E36 the big tipoff you were about to be locked out of your parked car was flickering dashboard items. On the E46 it's even more dramatic.

My E39 did that exact same thing when the battery started going south. Two weeks later it didn't start when I got up to go to work.

Replace the battery. BMWs from the E32 forward (CANBUS era) are extremely sensitive to weak batteries.

My E46's only symptom was that the regular key wouldn't start the car, even trying to bump start it. In desperation I switched to the plastic backup key and it promptly fired right up. That worked for about 2 days, then it wouldn't start at all. Replacing the approximately 10 year old battery solved the problem immediately. I didn't bother keeping the system hot with a battery charger, and had no issues.

My money's on battery, but failing that try the following, and this is going to sound really odd: flip down the passenger's side sun visor and see if the problem changes. On E39s at least, a failing ignition switch can be diagnosed by doing this - the vanity light coming on backfeeds current through the ignition somehow (I'm not sure of the specific path or reason, but it does).

Thanks guys. I'll check out the battery, but there are no signs of it going bad, like slow starting or anything like that. I can check it tonight when I get home. Thanks again.

In reply to bravenrace:

My E39 showed no signs of slow starting whatsoever until the day it didn't start. Seriously man, CANBUS electrical is weird. I wouldn't be surprised if the battery is putting out a voltage high enough to start and run the car, but low enough to cause weird electrical gremlins in situations where the alternator isn't picking up the slack.

In reply to pointofdeparture:

Is there a voltage cutoff point, or some other way I can verify its the battery before I buy a new one?

bravenrace wrote: Thanks guys. I'll check out the battery, but there are no signs of it going bad, like slow starting or anything like that. I can check it tonight when I get home. Thanks again.

Mine had no symptoms at all until it just refused to crank one afternoon when I came out from work at the end of the day. Once I switched keys it started as if there was no problem at all... for about 4 more starts.

Have the battery load tested. That will most likely reveal a failing battery. Could have a dead cell or intermittent internal short.

I've had bad alternators cause similar problems on e46 too.

From the BMW bible: "A Properly Charged BMW Battery has 12.6V as tested after having the car off and high beams on for 5 minutes."

A load test wouldn't be a bad idea either.

Load testing isn't an accurate way of testing batteries anymore. A Midtronics style battery tester WILL find a bad battery.

A lot of E46 bros replace them every 2 years, whether they need it or not. Not saying I endorse that approach, but it is out there. If it's over 2yr, go for it. Assuming you eyeballed the leads and grounds already.

Knurled wrote: Load testing isn't an accurate way of testing batteries anymore. A Midtronics style battery tester WILL find a bad battery.

I hope shops aren't even using the old "toaster" style load testers anymore. Digital load testers are the ONLY way to go. They still aren't perfect. I've had our midtronics tell me to charge and retest after charging four different times. Now the second time it tells me to charge and retest I just replace.

I had a e46 coupe that would randomly do this, lock the radio out, all the dash lights on, etc and somehow, some way by flipping down the passenger side sunvisor and sliding the vanity mirror on , it would fix the situation!

The strange thing is that it NEVER does it with the cruise control on, which is a lot on my commute to work, and it didn't do it this morning at all for the first time in a couple weeks, even though it was dark and my lights were on. It really seems to do it most when starting up. I experimented with it yesterday, and if I started up with low RPM's, it would do it almost every time. If I used more RPM's and was slower on the clutch (thus providing a smoother start up) it didn't do it at all. You guys have me pretty convinced about the battery, but I think I'll swap in one from one of my other cars that's pretty new before buying one. You know, back in the day I was a pro wrench, and you never had this kind of thing happen.

In reply to bravenrace:

Out of curiosity, did you try the official BMW 5-minute high beam test? Those symptoms totally sound like the alternator picks up the slack of the weak battery under load (cruise control, etc) but not at start when the battery is weak from minimal alternator charging.

Tyler H wrote: A lot of E46 bros replace them every 2 years, whether they need it or not. Not saying I endorse that approach, but it is out there. If it's over 2yr, go for it. Assuming you eyeballed the leads and grounds already.

Wow, that's just ridiculous. Mine lasted since I bought the car CPO in early 2006 until August or September of this year. So that's a minimum of 9 years under my ownership, and the car was built in September of 2003 - it was a BMW-branded battery that may well have been installed at the factory.

I agree! My 1999 E39 had a BMW battery dated 2005 when I finally had to swap it out in February. I've never had anything but the cheapest of cheap batteries fail in two years, and those were on cars with many, many other issues that probably contributed to the issue (hard starting, weak alternator, etc)...

Sooooo, related to this is the question of what battery? I actually have three cars needing batteries soon. For a long time I had been buying Optima batteries, but have heard stories of them not being as good as they used to be, and sure enough the last one I bought failed pre-maturely. So what say you?

OP, have you checked the battery?

Duke wrote:

Tyler H wrote: A lot of E46 bros replace them every 2 years, whether they need it or not. Not saying I endorse that approach, but it is out there. If it's over 2yr, go for it. Assuming you eyeballed the leads and grounds already.

Wow, that's just ridiculous. Mine lasted since I bought the car CPO in early 2006 until August or September of this year. So that's a minimum of 9 years under my ownership, and the car was built in September of 2003 - it was a BMW-branded battery that may well have been installed at the factory.

Yeah, replacing every two years is absurd, we had a BMW battery in my wife's car and it was only replaced preventatively when the alternator let go after eight years.

In reply to Harvey:

Not yet, I was busy last night drinking beer.