[mageeda]

I have not been able to open the trunk for months. there are 3 ways to open the trunk and none of them work,,, there is a button by the footrest, the button on the fob and button above license plate... none of them work,, this is the only thing wrong with the car.. i was told its the rear ecu module and when the trunk button is pressed no power leaves the ecu.. thats what the dealer said.. is this possible or can it be some other issue we are not thinking of?? i have checked the wires from ecu to actuator and all looks ok... they tried a new actuator and that did not solve the problem.. i checked the fuses under the trunk floor and all seemed ok,.. my questions... are there any other fuses? cani pull the fuses out of the rear ecu without messing anything up?? what else should i try>? the valet switch is unlocked, i fliped it back and forth a few times.. anyone else had this issue?? thanks the car was in a front end accident.. pretty bad.. could that mess something up?? we now have a wire running through the license light to pull emergency opening to open trunk..

[Drosif]

See if the actual mechanism is opening manually close the lock and use a screw drive to pull it open when pressing the trunk button at the same time to release the lock. The locking mechanism could just need extra lubrication to open it cuz the electronic could not have enough force to open the locking mechanism

[tracer bullet]

When you say it all looks OK, do you mean appearance? Or tested? I'd use a multimeter to be sure that you're getting power to the actuator, and further be sure the actuator is actually doing something or making noise.

[mageeda]

The mechanism is working as i have a wire to the emergency open wire and that opens the trunk... so its working...
there is no power getting tom the actuator - as there is no noise when the open trunk buttons are pressed. is this a bad rear ecu??? how to i check is there is power going to the mechanism? if there is no power leaving ecu is there anything i can do?
i said it looked ok as alot of people say look for a bad or broken wire..
all wires look ok.
is it ok to pull the fuses on the ecu?
as you can see when bmw pulled the harness off the ecu they did not even put the clamp back on it..
any ideas??

[tracer bullet]

A multimeter set to detect DC voltage should be able to tell you if things are being activated or not. Seems if the dealer can't figure it out they are just being lazy. They'd have wiring diagrams and almost certainly a meter and could start probing around to see what is and is not working. That's the gist of it what to do.

[mageeda]

they told me no power going from rear ecu to trunk actuator.. so i am wondering what would cause that... ?? is there anything i can try??
they want thousands of dollars to look into it or to replace rear ecu..
im looking for a possible fix here...

[tracer bullet]

FWIW it does sound like the ECU. You've tried several ways to command it to pop the trunk, and in none of the cases does it actually send any power to the actuator to carry out that command. And you know that the actuator works. So... it sounds like it's the ECU.

Can't guarantee it of course, but signs do point there.

You could try figuring out exactly which pins do that job, sending power to the actuator out of the ECU. Probe those and be sure that no power is coming out. If you detect power, then it could be the wiring after all. If you do not detect power at the ECU itself, then it does sort of guarantee that's your problem.

You could do one more step and be sure that the buttons are doing what you expect. find out for sure that they are making the circuit needed. It seems unlikely that all 3 ways to pop the trunk all failed at once, but you could still try and find out.

If you want to save a lot of money testing you may need to buy a multimeter and learn how it works. And find a wiring diagram as well.

[mageeda]

i tried all 3 buttons to open the trunk.. none do it.. no sound or clicking at the actuator... only reason i question the ecu is some bmw experts say if the ecu is going or gone it would have more problems then just the trunk..
my other question.. can i take the fuses out of ecu (in photo ) or will that do something bad?? if i want to check fuses...

[tracer bullet]

Originally Posted by mageeda

my other question.. can i take the fuses out of ecu (in photo ) or will that do something bad?? if i want to check fuses...

Should be fine. In theory you could disconnect the battery first but if the car's off I can't see anything bad that would happen. You'll lose power to any circuit of course, but only temporarily.

Checking fuses is actually an excellent idea, I should have thought of it.

I'd suggest you find a fuse diagram for the whole car, just to be sure you know which fuse to check. Or a wiring diagram, find the actuator and follow the wire path until you see what fuse it goes to and where.

A multimeter would let you check fuses without pulling them

[mageeda]

how to check fuses with multi meter without removing fuse? there are two dots of metal on back of fuse but its in a bizzare angle where i cant sit in truck and connect the two mutimeter prongs to the fuse...
i will try... i will also see if valet switch is connected properly..

[tracer bullet]

Originally Posted by mageeda

i will also see if valet switch is connected properly..

Good idea as well!

[mageeda]

There are 4 wires that go to the trunk actuator.. i tested them at the plug that goes on to actuator and 1 wire has 6.5v constant... other wires zero and nothing happens when i press the button.... any chance this means something???/ does that reduce possibility of rear ecu???

[mageeda]

any thoughts here... also when i press the button by drivers foot it makes some central locking hydraulic sound... same when i press trunk button on fob,, any ideas>???

[tracer bullet]

I was really hoping some 3 Series owners can chime in on this. I own and have owned BMW's but bot a 3 Series or I'd head to the garage and have a look at some things. I had hoped some basic troubleshooting would work, but you've done a good job with that it seems.

I'd consider finding a wiring diagram if possible, easier said than done sometimes. You'll want to know what wires come from an ECU, what are powered or are grounds, and so on. That 6.5V constant is odd, I don't know what to think of it. Normally it'd be 12-ish meaning battery power with car off, 14.X with the car running and the alternator spinning. Modern controls can change those numbers but speaking historically it'd be one of those.

Something must always be powered, "listening" for an input to open the trunk i.e. from the key fob. I'd suspect something wired to an ECU, which would then flip a relay to power the actuator. If nothing seems to make that happen, even the controls int he car, and you're sure it's not temporarily turned off i.e. with a valet switch... it would appear to be that ECU.

I wish I could help more. I think you're on the right line of thinking just have to keep at it. Identifying the wires and where they connect / what they do would be important to know.

If you end up feeling it is the ECU maybe you can work something out to buy it if it works, don't buy it if not (or, be able to get a refund). Even with a "restocking fee" or something to pay someone for their time loaning it to you.

[mageeda]

geeezz ya this is a tough one.. i even went as far as taking the valet switch out to make sure it was plugged in.. it is plugged it fine..
also i went over all wires from trunk latch to ecu.. they look fine/
when i disconnect the plug from the actuator/latch the power goes out to trunk light.. so they must be connected. the funny sounds the trunk button on fob and button near foot area are like a central locking hydraulic noise. so the fob / trunk button on fob is communicting with the car.. is there any better way to test the acuator without buying a new one?? no odb2 on this car?? i went through idrive.. there is a setting for trunk but its correct.... there is no hole for key on trunk.. button micro switch on trunk is ok..
any other thoughs??

[mageeda]

i wonder if i should re check fuses... other then just pulling and looking at them... maybe test them?
are there any relays for the trunk??

[tracer bullet]

Random thoughts only:

That noise is interesting, and it's good, it does imply something is listening / accepting inputs / trying to work.

I was think of how the valet switch works, does it open or close a circuit? Unplugging it might be the opposite of what's needed, or more specifically unplug it then put a jumper in place. If it's easy to unplug you could check that it goes from open to closed or vice-versa if it's just 2 wires. To confirm it's operational.

You were able to hotwire the actuator though, right? And make it work? I see that above. So it'd mean the actuator is fine. Well depending on precisely where you hotwired it, if it's past a harness connection then the harness connection itself could be suspect.

Can you have another person listen for that noise and see where it's coming from? Could be an important clue to determine what's making noise and what its job function is.

[mageeda]

You were able to hotwire the actuator though, right? And make it work? I see that above. no- cant get the actuator to work.. never heard noise from it.. i juts tested the wire and saw power on it.. thats all i got

[tracer bullet]

Sorry, I misunderstood. I read the wire you had as being for electrical supply to it, I see now it's a mechanical thing only. You aren't powering the actuator and it's working, you are pulling an actual wire the old fashioned way. Yeah that changes things.

So it could still be the actuator. I'd find a wiring diagram. See what wires bring electricity to the actuator to make it go. Then hook up your multimeter, press the key fob, and see if energy is sent to it or not. If yes, it might be the actuator that died. If not, it might be the ECU.

[mageeda]

i was going to do what you said and look for power on the specific wire going to actuator when pressing fob... but would i not have to also ground the specific ground wire on the plug? i only have 2 hands and that would be 4 ends of wires... any way you could look at a diagram and tell me what color to test????

[tracer bullet]

You put one lead on the wire in question, the other lead to ground (any bare metal part of the car), that's all.

LOL I was hoping some 3 series people could help more with this. If you manage to find a full wire diagram and I manage to have time, I'll give it a go.

Surely some 3 Series owners have read this?!?!?!

[mageeda]

I have now purchased a new trunk actuator and installed it.. no luck.. does not work.. no clicking no noise no nothing,.. now what????