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4th generation of BMW's popular 3 Series line of sedans and coupes.

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Changed battery in key fob, now car wont start

Locksmiths say they can fix it then never show up. Afraid to ask dealership to fix because of how much it could cost, but it is probably less than buying a new car. The car is 2005 BMW 325i with 150k miles. EWS3 with aftermarket key fob. Seems bonkers to me that changing a battery could cost me hundreds in repairs. Is this what BMW does now?

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Hi @theosnames

Try programming the key fob and check if that works

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This is part of the problem Ive been experiencing. The key does two things: opening doors and trunk and communicating with EWS which then tells the engine computer if it can start the engine or not. The sequence above only syncs the key with the doors and trunk. This was the reason why I changed the key fob battery in the first place. But, changing the battery also wiped the info on the key that talks to the EWS. I have done the sequence and the key opens doors and trunk wonderfully now. But i get no response when i turn the key in the ignition to start the engine.

Web searches almost always bring up this method of syncing locks. Sometimes the bring up a key programmer which reads the EWS and programs the key, but that only works on old versions of windows, probably because they are trying to hyjack the computer by exploiting a security leak.

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You lost the chip that talks to the security system. In aftermarket keys you have to program a chip with the same code as the original for it to work.

These chips aren't usually secured inside the key and can drop out if your not careful. It looks like a small piece of black plastic rectangular in shape. Open the key again and check. If you see a space similar then it's missing.

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That is weird, but then it is a BMW.

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OEM BMW keys for my car cannot be opened without cutting them open with a razor blade. The battery isnt supposed to be removed and is soldered in place. It is supposed to be charged by the ignition, but even then the battery will only last a few years.

I guess i have an after market key with replaceable battery because it snaps open and closed and battery is held in a sleeve where it can be slid in and out.

Either way, I called BMW and they can get me an OEM key fob by showing them my registration (so I dont have to tow the car to them) and by paying them $310. Hopefully the aftermarket key wasnt added to a place in the EWS 3 memory where the next OEM key is supposed to go. If it is, that could be a headache all on its own.

In the end, I would have to get a new key fob every few years either way, so i guess this is just another expense to expect for owning my BMW.

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Don't know about BMW key fobs, but my Toy fobs will start the car if I hold them next to the start button if the battery is dead.

Since this is an issue since you changed the battery, have you verified the LED lights when you push a button. If not the battery might be in backwards. It is also possible you got a bad battery. Happened to me once or twice.

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I know i changed the battery correctly because it opens door locks and trunk remotely which it didnt do before. There is no start button for the car. The key is inserted in the steering column and turned to start the engine. There are no LEDs on my key. My key looks liks this https://www.amazon.com/Beefunny-433MHz-A...

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Unless a BMW tech or expert on BMW systems can help, several options left; dealer diagnosis, expert locksmiths/ BMW EWS/programming, diy online factory service manuals from alldata.diy or Mitchell data. In theory with scant info, either EWS disabled your remote key code or the starter is dead. The simplest way to verify starter operation is; a fully charged battery or jumper cables connected to your battery, e-brake enabled, xmission in Park or Neutral, ignition OFF, front end jacked up for access to the starter and jumpering the starter small terminal to the large terminal with two wires (large gauge red battery cable and smaller fusible link wire going to the alternator). Jumpering these two terminals with a screwdriver, wire or needle nose pliers should result in the starter immediately powering to crank the engine. This bypasses the ignition switch and factory antitheft system to see if the starter will run. If the starter runs, the EWS/remote is the problem. No starter, replace it.

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