Key fob problems- strange!

Craiglxviii

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Hello everyone,

Thank you for the help offered so far, the advice has been invaluable.

The travails of my (newly acquired) W reg CL500 continue...

So today the fresh CR2025 batteries arrived and I have replaced the old ones in the key fobs. I now face an unusual problem.

1. Both key fobs lock and unlock the doors, and open/ close the windows. They only do this at ~6" distance from the drivers handle though. Is this usual?
2. Only one key fob (handily marked with a green sticker by the stealer) will operate the ignition. This key works fine, the other key goes into the dash recess and nothing at all happens.

Can anyone shed some light on this? Do I need a new fob?
 

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1. Both key fobs lock and unlock the doors, and open/ close the windows. They only do this at ~6" distance from the drivers handle though. Is this usual?

Not usual. The fobs have both IR and RF transmitters in them. The RF should work up to a few metres away and in theory the IR should be a bit less than that although many find it to only work at a few centimetres.

It looks like the RF isn't working. Since neither fob works at a distance it could be the RF receiver circuitry in the car that's faulty.
 
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Craiglxviii

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I forgot to add, I've checked both keys on my iPhone camera and can't see a thing. I can see TV/ Sky remotes so I know it isn't me or the camera.
 

television

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Hello everyone,

Thank you for the help offered so far, the advice has been invaluable.

The travails of my (newly acquired) W reg CL500 continue...

So today the fresh CR2025 batteries arrived and I have replaced the old ones in the key fobs. I now face an unusual problem.

1. Both key fobs lock and unlock the doors, and open/ close the windows. They only do this at ~6" distance from the drivers handle though. Is this usual?
2. Only one key fob (handily marked with a green sticker by the stealer) will operate the ignition. This key works fine, the other key goes into the dash recess and nothing at all happens.

Can anyone shed some light on this? Do I need a new fob?
Both of your keys will be OK, the IR is working, it is the RF long range that is not working, and you cannot see RF in a camera.

I would first check fuse 8 in the rear fuse box, there is a good chance that the siren has failed and blown fuse 8.

Is the radio reception good on weak stations.
 

Lance

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I've described another problem in another thread whereby the keys on the W203 I recently bought either open the doors or operate the ignition but both keys don't do both. Each key does either one or the other!

Malcolm is very kindly going to try and fix at least one of them so I will see how that pans out.
 
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Craiglxviii

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Both of your keys will be OK, the IR is working, it is the RF long range that is not working, and you cannot see RF in a camera.

I would first check fuse 8 in the rear fuse box, there is a good chance that the siren has failed and blown fuse 8.

Is the radio reception good on weak stations.


The radio reception seems fine so far, I had a scan through and picked up most everything I'd expect to.

By siren do you mean the horn? If so then there's nothing wrong with it, the missus decided to try it out while I was opening the bonnet and I nearly s**t myself at the noise.

Fuse 8- I don't have a fuse box map (not in the toolkit, there are a few bits missing which I'd like to try to source- although a very natty threaded aluminium handle for something is there, what it fits to I have no clue!)- can you tell me what current rating please and I'll pull all and check.
 

television

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The alarm siren is nothing to do with the cars horn. The siren fuse in the rear will be about 7.5 amp



The little round bar with threaded end is for help when fitting a wheel, screw it in a hole and lift the wheel onto this little round thing, dead simple and easy.
 
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Craiglxviii

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Thank you again for your help!
 
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Craiglxviii

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All fuses in the rear fusebox are fine. 1 x 5 and 1 x 7.5A are the smaller fuses. So that's a no go...
 

television

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Then the OCP needs to be checked, the antenna terminates in this OCP (overhead control panel)

There was a good post on this on a 215 a little while back, it may come up on a search
 

Lexman8

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I forgot to add, I've checked both keys on my iPhone camera and can't see a thing. I can see TV/ Sky remotes so I know it isn't me or the camera.

This is weird. The symptoms suggest that RF isn't working but this indicates that IR isn't working (assuming the OP pointed the IR emitter correctly at the camera).
 

Naraic

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I forgot to add, I've checked both keys on my iPhone camera and can't see a thing. I can see TV/ Sky remotes so I know it isn't me or the camera.

The IR is not working...but I suspect you know that.
 

television

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The IR is not working...but I suspect you know that.

If the key fob is operating the windows, then IR is OK, you cannót open the windows on RF.

If the car locks from a few meters away, then all is good.
 
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Craiglxviii

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Car unlocks and locks with the fob pressed against the IR sensor on drivers door only (seemingly).

Windows power up and down easily enough from a metre or so.

Both keys will do this but only one will turn ignition lock.

Interesting post re the OCP. It's totally dead, replacement unit winging its way from America via eBay as we speak. I didn't know that would affect key fob range!
 

television

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If only one key turns, then the one that does not is at fault (I can fix some where the coil has broken off). You should check the OCP fuse.

The RF antenna terminates in the OCP where it goes via the CAN
 
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Craiglxviii

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Hi Malcolm,

You're turning into my resident MB "guru" and I really do appreciate your insight and experience.

I checked the OCP fuse (f77 I believe) and is fine, hence buying the replacement.

Car now down at local Indy for fluids & filters change and sorting brakes out, can't do anything til he's finished now.
 

television

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I have fixed the key that you sent, the transponder coil had broken off.

The case is in a bad way and for a few ££ you can buy a new one on Ebay.
 

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