electrical issues

[jaffar]

Hi all

Two days ago, my airbag dash light came on. I was not too worried, as I already heard this may be a "common issue". After I got to work and the car sat for a few hours, the light even went away. It came back after a few kilometers though.

While looking for a service with a diagnostic computer, things evolved:

- the radio turns off and on by itself (also does not turn off when I stop and take out the key, or does not turn on when I start the engine)
- the interior light turns on and off by itself, or just sort of blinks, like someone is playing with its wires
- the steering wheel controls for the radio stop working randomly (but the gearshift paddles still work)
- the wipers/washers work from time to time
- the horn works from time to time
etc.

Basically all modules have gone insane.
One time, the engine would not start. It was rotating but not starting. Took a couple of minutes of trying to get it running.

I went to a service and looked at the errors - the first one was the airbag module complaining about undervoltage.
They cleared all the errors, but they come back as soon as I start the engine.
They said it's a "common problem" with the Z4 and proposed to check the airbag module for bad contacts. They said the airbag module is acting up and is sending "bad signals" over the KCAN and is making all other modules crazy.

They also checked the battery with a tool and said it's in good shape. Voltage with engine running is 14.07V so the alternator/charging relay seems ok, too.

I took out the battery for a few hours, nothing changes. I also tried to charge it overnight, just to be sure - does not help.

Any suggestions are welcome.
Thank you

[Vanne]

how old is the batt? id start with that, as thats probably the cheapest to replace, and unless its six month old..

[jaffar]

The battery is from 2010. It has been verified with some "smart" device and turned out good.

To be sure, I just tried with a brand new battery from another car, same symptoms.

[shock311]

I have similar issues but not to the same extent. My issues are the airbag light comes on and my radio volume control stops working and my instrument cluster lights go out (in otherwords, all indicators are non-responsive but the actual functions still work, i.e. turn signals, headlamps, etc).

I had replaced my ignition switch thinking that may help based on what I've read, hasn't. My battery is new and so now I'm going to tackle the seat occupancy sensor. I'm going to try to bypass this as found in this thread: http://www.zpost.com/forums/showthread.php?t=797110

Hopefully that helps resolve this issue as unfortunately my car isn't under the VIN range for the associated "reimbursement".

[jaffar]

Testing some more - I checked all the electrical connectors, all are clean and in good shape, wires are not damaged anywhere visible.

Then I had the idea of unplugging the Airbag Control Unity - magically, the car is working correctly again, all modules do what they are supposed to.

While this does not necessarily mean that the unity itself is broken, it would point to it.
Did anyone ever replace the capacitors inside it ? One (left) looks a bit swollen, otherwise the unit looks perfect, there's no trace of water or oxide.

If I go ahead and replace the unit with one from a scrapped car, do I risk anything ? I mean, scrapped cars usually come from accidents, do I risk the "new" unit exploding the airbags in my face, or doing anything funny ? Can the crash memory be erased from it, as my car has never been in an accident ?

Thank you

[StickMon]

Can't speak for the integrity of a used one, but I would replace the entire unit.
The puffy cap might have over heated, but that might not mean it's bad.
It may be a symptom of something else that made it overheat.

My guess is those store the charge needed to set off the bags when there's no other power.
A problem with the charging circuit may be charging the one on the left too rapidly.

[swifttiga]

Did you ever get this sorted? I have the same problem looking for a fix that works.