Did I Fry My Key?

[Jehu]

If I had the two batteries in the key the same way,one in the wrong way for about 12 hours could that damage the transmitter? I have still not figured out why the locking system won't initialize with the key. I've replaced a sticky door actuator and all the locks work when using the key in lock to lock or unlock,even the trunk lock when locked locks the doors and the fuel door ... I just bought a brand new truck actuator because when the remote system was working the key button never locked or unlocked the trunk so I assumed it was bad or one of the wires in the trunk was broken to the actuator.. I checked and repaired any damaged wires. First off If the key locking the Trunk locks the doors too that means the actuator is OK doesn't it? So my problem seems more likely either the key transmitter or the receiver ,either that's not sending the command to the GM or not getting a signal from the key even though the LED on the Key lights up.. I may make a pain in the neck out of myself repeatedly bringing this up but I can't see just forgetting about the whole system for good ... I have to think someone somewhere sometime had this happen and found the fix..

I've tried Battery Resets... taking the Neg cable off,pulling the GM and the RM... putting them back in and reconnecting the battery.. I've scoured the Web searching the topic and found no solutions... I've had a dealership scan the 20 pin connector and tell me to replace my front latches and actuators for a "Door Open" fault code... I've checked the wires for the receiver antenna in the Rear View Mirror which are ok.. I know the Alarm works because when I either disconnect that plug or remove the fuses under the back seat for the the Alarm goes off.. I get the feeling I'm going to have to place a call to BMW USA for some old time engineers in De who know the system because nobody has a clue here..

[Adnan]

[QUOTE=Jehu;325179]If I had the two batteries in the key the same way,one in the wrong way for about 12 hours could that damage the transmitter? QUOTE]

Hi,

Not having looked at the insides of the key, I would assume that the two batteries are meant to be connected in series, providing 2.4 or 3 volts, depending on the chemistry. If you put one battery in backwards, that would mean that the net voltage seen by the circuit is zero. Schematically, the two anodes were connected, and the cathodes went to the circuit in the key.

My guess would therefore be that you didn't damage anything. The circuit wouldn't work at all, but no harm done. If the batteries were designed to be in parallel (highly unlikely), then putting in one backwards would promptly short the two out but again, no damage to the circuit unless the batteries overheated and did thermal damage.

Regards,
Adnan

[Adnan]

Me again,

If I understand you correctly, you're saying that the locks behave correctly in all respects in manual mode, that is, when using the key physically. The remote's LED lights up but the GM doesn't respond.

If my interpretation is correct, there are a couple of things to consider. One is that even though the LED lights up, it doesn't mean the transmitter works. These things probably use what's called ASK modulation, where the RF works on 433.92 MHz or 315 MHz or something similar. To keep costs low, the transmitter probably uses a SAW resonator but they are prone to drift over time. They can also break. Have you dropped your key recently?

The best bet would be to get to the GM and if you know which pins are the receiver, put an oscilloscope on them to see if the transmitter's signal is showing up. Do the same on another E34, or better yet, borrow someone's key. That will tell you whether it's your transmitter or your receiver that's misbehaving.

Hope that helps,
Adnan

[Jehu]

Me again,

If I understand you correctly, you're saying that the locks behave correctly in all respects in manual mode, that is, when using the key physically. The remote's LED lights up but the GM doesn't respond.

If my interpretation is correct, there are a couple of things to consider. One is that even though the LED lights up, it doesn't mean the transmitter works. These things probably use what's called ASK modulation, where the RF works on 433.92 MHz or 315 MHz or something similar. To keep costs low, the transmitter probably uses a SAW resonator but they are prone to drift over time. They can also break. Have you dropped your key recently?

The best bet would be to get to the GM and if you know which pins are the receiver, put an oscilloscope on them to see if the transmitter's signal is showing up. Do the same on another E34, or better yet, borrow someone's key. That will tell you whether it's your transmitter or your receiver that's misbehaving.

Hope that helps,
Adnan


Great.. very helpful Adnan. You've got the idea correctly. I was reluctant to consider any physical defect as the only two factors to differ between the working state and Non working was the time without charge and the attempt at initializing with the door open by mistake. Since the system was scanned by a BMW Dealer I figured that clears any stored fault codes and hoped it would just resume operation. I'll look into the GM Pins and see what I can do with that.. It would if I can find the right pins of course prove weather the key was at fault.. I don't yet know anyone in the area with the same kind of System .. Thanks very much for your thoughtful help.

[whiskychaser]

You might be hard pushed to find someone with an oscilloscope but may know somebody who is into amateur radio and has a frequency counter something like this:
http://cgi.ebay.co.uk/FC-1-Portable-Frequency-Counter-10Hz-2-6GHz-Ham-Radio_W0QQitemZ330330541798QQcmdZViewItemQQptZUK_C onsumerElectronics_SpecialistRadioEquipment_SM?has h=item4ce93c0ee6&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1690%7C 240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50
It will pick up if your fob is transmitting and on which frequency. If you dont know anybody, just keep an eye out for a beam aerial like this:
http://www.hamradio.co.uk/acatalog/Ant_Amateur_Tonna_T50.html
The owner is bound to have one. They will probably be delighted to help. But you may have to listen to an enthusiatic lecture in return:D