E46 alarm key fob working only intermittently

[to3m]

The key fob for my E46 has stopped working reliably. It's failed to work a handful of times in the past, but it's becoming much more regular. A couple of times I've got bored of clicking the button and have unlocked the door by hand, which activates the alarm until I put the key in the ignition. (Luckily yet to happen after 10pm.)

As far as I can gather, there are two likely causes for this: dodgy key battery (potential DIY job), or dodgy sensor in the car (££££££££). Is there any way I can cheaply/quickly figure out whether it's one of these two? Unfortunately my car only came with one remote key, so I can't do the obvious thing of just trying the other key Locking does seems marginally more reliable, though, suggesting it could be a battery problem...

And meanwhile, is there any way I can activate the alarm without using the remote control?

Edited by to3m on Wednesday 19th February 21:47

[jumpingjackdan]

Key fob DIY on youtube: https://www.youtube.com/watch?v=e1o9vH3mgmg

Given you only have one key it might be risky if it goes wrong but it looks easy, plus the video poster seem to have the same issue as you are describing. If not, you might have to go to the stealer.

[to3m]

Well that doesn't look impossible, and a suitable battery is £7 from Amazon, so that's now on my to do list... thanks!

Anybody know if you can reprogram the key using the wallet key? It opens the door and will deactivate the alarm once in the ignition so I'd assume you can, but I'd rather not find out the hard way that it doesn't!

(I assume the valet key can't be used for reprogramming, as that would be a bit of an obvious security flaw, given its stated purpose?)

All the guides I found deal with reprogramming a keyfob key - either a new one, or one that's had the battery changed - when you've already got a working keyfob key to hand...

[Clivew]

A common problem with the E46 central locking is when the car is locked the doors won't unlock with the remote key, but the interior lights come on. There isn't a problem locking the car or with unlocking the boot. This is due to the failure of a couple of relays located in the GM5 module behind the glovebox. BMW look for around £400 + VAT for a new module but it can be fixed for about £56 if you have a pozidrive screwdriver and a pair of pliers as I discovered last weekend.
The guy on ebay was fantastic, phoning me to let me know he had received the module and that he was posting it back the same day.

http://www.youtube.com/watch?v=b0zT2UtEU88

http://www.ebay.co.uk/itm/BMW-Central-locking-GM5-...

Edited by Clivew on Thursday 20th February 22:43

[to3m]

Just in case anybody cares, the battery arrived today. It took a surprisingly long time to get inside the key (and I made an real mess of the sides doing it), but once I'd done that part, I soldered in the new battery and the key now appears to work reliably again.

And fortunately, since I have no spare, no reprogramming was required.

[Clivew]

Thanks for the update, glad it was an easy fix.

[RC1]

It's on my list. Any chance of linky to battery

[to3m]

I got it from here: http://www.amazon.co.uk/gp/product/9792254285/ref=...

Once I'd got the key open I cut the original contacts so they were in roughly the right place for the new battery (bonus: this also means you don't have to unsolder the original battery), folded the new battery's contacts round the stubs, and then popped a bit of solder in to make sure the contact stuck.

There's not much room in the case though, so before attempting any of this you might want to make sure that your soldering skills are better than mine - so afterwards I decided not to bother trying to glue the two halves of the key back together (like they would fit any more anyway...) and just fastened it up with a few layers of black electrical tape. The best I can say about this is that it doesn't look as messy as you'd think, but for a saving of £145 I think I'll be able to put up with it.

[Ruskie]

I was under the impression the key was rechargeable via the ignition and hence you never need a new battery or has yours just perished?

[to3m]

Batteries only have a finite lifespan, and I assume this one had just reached the end of its life. I've had the car for 3 years and the key has been generally reliable up until now.

My car was manufactured in September 2001. I'm guessing the key will date from around then too. Maybe I'm being pessimistic but I don't think it's too surprising.

[DJFish]

I did mine this afternoon as I got fed up with tapping the bloody key against the roof rails every time I wanted to lock or unlock.

I bought the battery on ebay, making sure to buy one with the soldered terminals at 12 & 3 o'clock (or 90 degrees apart if you're scientifically minded).

When I got the old battery out I saw the negative terminal had snapped off just short of the soldered joint causing the intermittent fault, once the new one was in it worked a treat and didn't need re-programming.

Well worth doing!

One thing puzzles me, although the battery is re-chargeable, it's not connected to the key blade by any metal so I'm curious how it actually re-charges in the car.

Edited by DJFish on Saturday 24th May 21:54

[Mave]

I think it recharges through an induction coil.

[DJFish]

That would make sense......

[bench33]

My mate just bought a 325i and the key fob fob occasionally opened the boot or unlocked the car but wouldn't lock it. The lock switch had come off of the PCB so i soldered it back on but still wouldn't lock and other functions were still intermittent. I tested the battery and it was OK. Eventually found that the insulator under the battery had worn away and must have allowed the battery to short on a pcb track. Tore off a piece of a kebab shop menu and put it under the battery and now works perfectly.

Edited by bench33 on Saturday 8th November 22:47

[dr_gn]

to3m said:

The key fob for my E46 has stopped working reliably. It's failed to work a handful of times in the past, but it's becoming much more regular. A couple of times I've got bored of clicking the button and have unlocked the door by hand, which activates the alarm until I put the key in the ignition. (Luckily yet to happen after 10pm.)

As far as I can gather, there are two likely causes for this: dodgy key battery (potential DIY job), or dodgy sensor in the car (££££££££). Is there any way I can cheaply/quickly figure out whether it's one of these two? Unfortunately my car only came with one remote key, so I can't do the obvious thing of just trying the other key Locking does seems marginally more reliable, though, suggesting it could be a battery problem...

And meanwhile, is there any way I can activate the alarm without using the remote control?

Edited by to3m on Wednesday 19th February 21:47

Thanks - you said opening by hand activates the alarm? It doesn’t on mine. In fact locking by hand doesn’t seem to switch the alarm on - at least the mirror light doesn’t flash.

[ian332isport]

dr_gn said:

Thanks - you said opening by hand activates the alarm? It doesn’t on mine. In fact locking by hand doesn’t seem to switch the alarm on - at least the mirror light doesn’t flash.

Alarm activation by the key in the door lock is something that can be turned on/off by coding.

[to3m]

dr_gn said:

Thanks - you said opening by hand activates the alarm? It doesn’t on mine. In fact locking by hand doesn’t seem to switch the alarm on - at least the mirror light doesn’t flash.

Now you're asking! - this was years ago now... I think I found locking was a bit more reliable than unlocking, presumably because the key's knackered battery had been charged very slightly by the journey. So I'd sometimes have to unlock an alarmed car with the wallet key, which as I recall would cause the alarm to go off until the wallet key was used to turn the ignition.