central locking system problem

V

v8z4

Member
 Fountain Hills, AZ
Car is a 2003 Z4 2.5i roadster.

Setup:
Today I was out running errands and everything was going fine. Stopped at a store and when I got back into the car and cranked it, the emergency flashers started flashing (blink blink blink) like I had pushed the center console button, the engine stumbled and died. I cranked the engine again and it idled fine.

Issue:
However, when I tried to lock the doors (pushing the console door lock button), nothing happened (no lock). I tried several times without any result so I cut the engine off, got out, and tried the key fob. Again, nothing happened. Thinking it might be a fuse in the central locking system, I pulled both fuses to find them both in good order (not blown). Once the fuses were put back in, the door locks operated as they should.

So, I went on with my errand running and several hours later, the same thing happened again (got in, cranked, flashers flashed, engine stumbled and quit, door locks wouldn’t work). I again pulled the central locking system fuses and the door locks operate as they should.

What could be causing this?

Thanks,
Chris
 
Be sure your battery is strong and healthy. A weak battery has been the culprit in many bizarre electrical behaviors.
 
It's a brand new Odyssey PC680 battery, though it could have been low on charge (small battery + shirt trips = not enough time to recharge). I'll stick the battery charger on it and see if the problem returns. Thanks.

Edit:
On second thought, it can't be a low battery issue. When this happens, the engine is cranking fine (no slow cranking), dying, and cranking fine again. If the battery was low, it would have a hard time cranking. I know this because I have run the battery down before (when I was installing the amp and testing....). When the battery is low, it cranks hard but once fired over it idles just fine. This is something else (I think).
 
The engine electronics is completely separate from lighting and central locking, so the battery was the only thing in common I could think of. Wouldn't hurt to have the current output checked, wouldn't be the first new battery to be defective. I get what you're saying about weak battery symptoms, and you're right. My thinking is the cranking stresses the battery enough to lower the voltage enough to cause the electronics to balk. The battery still has enough current capacity to crank the engine, albeit at a lower than normal voltage.

The starter is not nearly as voltage sensitive as the electronics, it mainly needs current. If you current test the battery, you may find the recovery voltage is below spec. I admit it's a stretch, but otherwise, I'm stumped. Good luck!
 
Okay, so I had the battery checked and it is good.

I ran around all day without problems, got to my last stop (had to pick up the wife) and sat outside idling for about 20 mins (105 outside). I had to cut the car off to go inside to help her bring some stuff out and when we got in, problem surfaced again. The engine cranked, the emergency flashers started going, I though "oh s*it", had to floor the peddle to keep the engine running at all, after 10 seconds of this I cut the key off. Re-cranked without any issue except for no door locks. Cut off again, pulled/re-installed the 7.5amp central locking fuse, door locks worked as normal.

So, long story short it seems like this issue is related to heat. I have NEVER had this issue when it was cooler outside (got the car in February so this is the first summer I have owned it) and the issue seems most prevalent when the car has been sitting idle and is perhaps heat soaking something.


Here is the reply I got over on bimmerforums.com
First thing: get the battery checked - low voltage make the BMW's computer do weird things. If its not that have the alternator checked out as well.

If both above are good, was it pretty warm out when this happened? You could be seeing the beginning of total relay failure in the GM5 Module (handles pwr locks and windows). Its pretty normal for cars this old.

Not to hard to replace once you get it fixed or get a new one.
Best route if you are not a electronics tech with good desolder skills and equipment:
http://www.bmwgm5.com/

I had same problem in my 2003 330i. I was able to replace the relays myself but its not that much more expensive to send it to the guy on the website. Especially compared to a new one.

Otherwise it could be the door lock actuators. Some info on the above website pertaining to that as well.

Good luck
Bruce
Click to expand...

Now the odd thing is why? As we all know, the engine is controlled by one computer and the interior stuff by another. Why the engine would want to die and the door locks go out like that, it doesn't make since.

One possibility I thought of, how do these cars handle security? Are the keys imbedded with any chips? Could the internal computer be dying and as such when hot it doesn't read the key right, thinks the car is being stolen, and freaks out? (I know.... long shot but... I'm stumped)
 
Kinda wish it was the battery, not so I'd be right, but because it would have been an easy fix. This is getting complicated.

Good thought on heat, hasn't been too hot here, so didn't occur to me. Interesting thought on security system, except that brings a 3rd module into play. There is a chip in the key, it interfaces with a security module that in turn interfaces with starter and DME/ECU modules. Still has nothing to to with central locking and lighting.

I think the relay avenue might be worth pursuing. My concern is 're-booting' the system with the fuse seems to work, which would indicate a firmware problem, not relay. I think. Unless reinstalling the fuse cycles the relay to get it unstuck? Do you hear clicking when you reinstall the fuse? The relay is in a metal box close to the fuse block. Some people have had positive results having the general control module re-flashed, but I doubt it would help if it's heat related.

To further complicate things, it looks like the general module only manages interior lighting and central locking. The exterior lights are controlled by yet another module! Arrrgh!

I agree that the engine issues are maybe not electronic, but mechanical, related to heat soak or vapor lock. Unfortunately, not easy to find and cure the problem. Not my area of knowledge as it doesn't really get all that hot here.

Still don't have an explanation how the two (three? four?) problems are triggered simultaneously. You, know, there is one thing these modules all share: the K-bus. A digital line for exchanging information packets about vehicle state. How's this: Car thinks it's been in an accident. Shuts off engine, turns on flashers, unlocks doors, puts the locks in a state where they can't be re-locked accidentally. The problem would be the heat affecting whatever sensor determines there's been a crash. Triggered by brief voltage drop while cranking the engine, despite healthy battery, but because of unhealthy sensor.

Crazy? Yes. Long shot? Yes. But it DOES explain everything. Might be worth getting checked out. There may even be trouble codes stored, but not severe enough to trigger a warning light. The engine certainly should have stored some trouble codes. I think it's worth checking for any codes stored. it may give you a better direction to pursue. This may be beyond the basic OBDII code check, you may need BMW diagnostic computer for this one, either dealer, indy, or very well equipped owner.

Sorry for the rambling, the ideas came to me as I was typing, couldn't see an easy way to re-compose.
 
Hey, funny you should come up with that.

Last night I emailed the guy who "rebuilds" the general modules and his reply was as follows:

The GM5 can not do most of the things you are having problems with. The GM5 does not have control of the hazards, it can not kill the engine nor can it inhibit starting. It does not authenticate the keys and it has no control over the security system. The GM5 simly can't do he things you say happen.

Try pulling the airbag fuse(s) and drive around.
Click to expand...

Seems he might be hitting on the same issue you are thinking (false accident situation). I pulled one of the airbag fuses (couldn't pull both cause some other things seem to feed off the circuit). I have not driven the car yet but I'll cross my fingers.
 
Cleaning out my notifications I realized I never wrote back on this. Pulling the airbag fuse solved the issue. Because the airbags have been removed, the circuits are open and the airbag system must thing a wreck has occurred thus preventing locking. With the fuse pulled, the airbag computer is disabled and thus not interfering with the locking system. Have not had an issue in months.
 
I have actually same model Z4 2003 2.5l and locking system drives me crazy since I bought this car. Guys are you understand the mechanism of the locking system, it looks like it's plenty of modes how this car is unlocking doors with and without the roof or windows position. Today for example I couldn't open door from a driving side at all with the keys in the lock. Car decided do not let me in and wanting to hold the key button to automatically open windows and roof instead. Usually when I close the door it automatically lock the door from inside and I need the keys again to open it manually (I left keys few times inside, you can imagine it was nightmare to get inside without keys...terrible experience). In some mode it turns head up light on when I open the doors, I have no idea when it switching that modes, probably depends from when I lock the car with roof down or windows down and then it changed entire mode to different one. How to figure it out?
 
Popo90 said:
I have actually same model Z4 2003 2.5l and locking system drives me crazy since I bought this car. Guys are you understand the mechanism of the locking system, it looks like it's plenty of modes how this car is unlocking doors with and without the roof or windows position. Today for example I couldn't open door from a driving side at all with the keys in the lock. Car decided do not let me in and wanting to hold the key button to automatically open windows and roof instead. Usually when I close the door it automatically lock the door from inside and I need the keys again to open it manually (I left keys few times inside, you can imagine it was nightmare to get inside without keys...terrible experience). In some mode it turns head up light on when I open the doors, I have no idea when it switching that modes, probably depends from when I lock the car with roof down or windows down and then it changed entire mode to different one. How to figure it out?
Click to expand...

It sounds like you need to check and see how your GM 5 has been coded. It also could be door lock relays in the GM5. After 10-15 years of use the contacts just wear out and you need to change the relays.
 
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