can someone explain to me, why it wont start the car after changing the battery?
I have a dumb key (without buttons) and that one starts the car, how come the dumb key without battery or anything starts the car? but the one with new battery it turns but it wont start

interesting update:

I replaced the old BMW e46 Key with new battery, and quite interestingly This one ALSO emmits signal only for Lock Button. (using Woyo tester that was recommended in this thread)


is possible that the Tester only able to detect signal from Lock button ?
this old key belongs to a car that I had many years ago (that got totaled) but at that time I remember the keys were working fine. so I put new battery in it. but the tester only shows it recieves signal on Lock Button.


Another interesting finding is, I tried to Pair it with my car, and pairing did not do anything. and also it did not start the car (I started the car with Dumb key) and then it let me start the car with e46 board couple times then it did not allow me to star the car with the E46 board key.

so I am thinking ....maybe my keys are Fine ? and the problem is something in my car?


has anyone else Tested bmw keys with woyo testers? do they actually detect signal for unlock buttons too ?

Sounds like something is wrong with your car. The key shouldn't even need the battery in it to start the car. The battery is only for the lock/unlock/trunk commands.

But my dumb key (the one without any buttons starts it fine) it only happened after I replaced the key battery before that i could start fine with the defected key


I know even old honda civic cars have some sort of of chipset encoding that a normal duplicate key wont work (i learned from locksmith in home depot) so maybe the chipset for my key got reset aftwr battery change??

Do we know it pairing is needed after battery’s change?

Chances are that you have damaged the PCB (or some components) while changing the battery and this has killed the EWS function. :(

And you would not be the first to have this issue... :rolleyes:

Have a read of this post by Qsilver7: -

https://xoutpost.com/1119011-post3.html

your testing method is flawed. you are testing an unknown quality key and expecting for all functions to work and thus doubting the test results.

the battery in the remote is only for the the locking/unlocking/tail gate features only. the toroidal coil/key ring on the steering column will supply power to the transponder/coil on the remote to authorize starting.

you have most likely damaged the coil on the remote. a simple check with a multimeter would confirm this.

your best bet is to leave the windows down, park the car outside with the key in the ignition and hopefully someone will come along and steal this car from you. this way you can confirm the key works or not.

Yes, pretty much all modern cars for 20+ years (to my knowledge) have a passive chip in the key which is scanned when inserted into the ignition cylinder. It does not require a battery for this chip to work because it is a passive device. That chip is totally separate from the battery in your key and will work even if the battery is dead.

It sounds like you've checked to verify that the key is broadcasting the "unlock" command with this tester you have (never used one of these but it sounds like you know what you're doing). Next, do you have a Foxwell or BMW Scanner or something which you can use to find out what the car thinks about the key you are using? These tools will tell you which key is inserted and whether it is authorized. If it starts with certain keys but not others, it may have suffered some kind of error (or been reprogrammed by something you've accidentally done) which is preventing your key from starting the car. But you can be sure that this fault is not related to the battery in the key.

Wpoll's suggestion is definitely something to look into, however I have no familiarity with this fault, so I can't be of any help in that direction.

To answer your last question, pairing may be necessary to get the key lock/unlock functions working after a battery change, but shouldn't be necessary to get the car to start with that key.

ok final update:
I did order a new key here, and everything works perfect now.

and the tester does show frequency for all the buttons, so it seems like my old key problem was not battery but one of the switches were defective