W203 class central looking will not work, although car can start and drive with the key fob. What part needs replaced.. any help appreciated.

[Mikec180]

W203 class central looking will not work, although car can start and drive with the key fob. What part needs replaced.. any help appreciated.

 

[DSM10000]

Do you have two keys, if so is the central locking not working with either?

Have you checked the batteries in the key fobs?

Start with the simple things first.

By the way, are you aware that the key will still operate the ignition regardless of the batteries in the fib, the batteries are only there to transmit the radio signal to lock or unlock the car.

If changing batteries doesn't work then there may be damage to the circuit in the key. Dry solder joints are not uncommon.

There is also a receiver that picks up the signal from the key fob, these can fail and cause the problem you describe.

 

[m80]

Is the car locking from the dash button? To eliminate an issue with the car.
You can try pointing the fob at a digi camera and pressing, you should see a red light in the camera monitor.
The fobs can also lock by holding the fob close to the black square on the drivers door near the handle.

 

[Mikec180]

Do you have two keys, if so is the central locking not working with either?

Have you checked the batteries in the key fobs?

Start with the simple things first.

By the way, are you aware that the key will still operate the ignition regardless of the batteries in the fib, the batteries are only there to transmit the radio signal to lock or unlock the car.

If changing batteries doesn't work then there may be damage to the circuit in the key. Dry solder joints are not uncommon.

There is also a receiver that picks up the signal from the key fob, these can fail and cause the problem you describe.

The fob is less than 6 months old as the original was ruined during a hot wash cycle...
Thanks for your time

Is the car locking from the dash button? To eliminate an issue with the car.
You can try pointing the fob at a digi camera and pressing, you should see a red light in the camera monitor.
The fobs can also lock by holding the fob close to the black square on the drivers door near the handle.

The lock button on dash works... Will try your suggestion and let you know. Cheers

 

[whitenemesis]

The fob is less than 6 months old as the original was ruined during a hot wash cycle...
Thanks for your time

It may well be but it doesn't rule out a problem with it
Do you have a second fob to try?

 

[Mikec180]

No secondary key Done the basics and now works to lock and unlock all doors...But only if fob is close to IR sensor. I suspect its the cheap battery I had in the garage will invest in a better quality of battery today. And fingers crossed that will be the solution. Thanks all for your great input.

 

[whitenemesis]

What were "the basics" that you have done?
It could be a weak battery, could also be a failing antenna amplifier in the car. If a new battery doesn't work get the codes read using STAR and see what's going on.

 

[Diesel Benz]

No secondary key Done the basics and now works to lock and unlock all doors...But only if fob is close to IR sensor. I suspect its the cheap battery I had in the garage will invest in a better quality of battery today. And fingers crossed that will be the solution. Thanks all for your great input.

Great to see optimistic people. I would have suggested getting prepared for repairing the rear window antenna amplifier (or contacts).

Also unnecessary to spend money on a spare key. At most wait till the key dies or gets lost and purchase a new key on the previous week and you're good!

 

[m80]

Great to see optimistic people. I would have suggested getting prepared for repairing the rear window antenna amplifier (or contacts).

I wondered if the rear window antenna served the locking system also.
A clue to that having come adrift would be poor FM reception.

 

[cheddar]

check the fuses in the boot, there is one (7.5amp) that covers the RF antenna signal amplifier that also powers other things, sometimes blows due to a faulty alarm siren.

 

[Diesel Benz]

I wondered if the rear window antenna served the locking system also.
A clue to that having come adrift would be poor FM reception.

I understand this is a W203 car, the rear window would then have 4 separate FM antenna. The first one serves for the radio remote control too. If the amplifier is bad or all contacts lost, FM radio would not work. If only one antenna connection was bad, the FM radio would still work pretty well with antenna diversity. I have no idea if all contacts typically fail at about the same time.

 

[Bemmy]

Hi All, I have a 2005 W203 and the key fob has stopped working for the central locking.
I have put new Duracell batteries in - I have the red LED working.
I've checked the 7.5 amp fuse in the boot (it's not blown).
I've run the Torque fault code finder - nothing found.
I can central lock using the buttons on the dash.
The car will start using the fob.
I've even tried the sync method posted in another thread - didn't work.

When pointing the fob at my iPhone camera I DO NOT see the infra red flash so I guess the fob is kaput? or is this an iPhone anomaly?

Any advice gratefully received before I part with a lot of cash on a new fob!

 

[Diesel Benz]

Hi All, I have a 2005 W203 and the key fob has stopped working for the central locking.
I have put new Duracell batteries in - I have the red LED working.
I've checked the 7.5 amp fuse in the boot (it's not blown).
I've run the Torque fault code finder - nothing found.
I can central lock using the buttons on the dash.
The car will start using the fob.
I've even tried the sync method posted in another thread - didn't work.

When pointing the fob at my iPhone camera I DO NOT see the infra red flash so I guess the fob is kaput? or is this an iPhone anomaly?

Any advice gratefully received before I part with a lot of cash on a new fob!

Which sync method are you referring to? A 2005 key does not need any sync. If the key starts the car, it neither needs the trick to press buttons to wake it up just when inserted to the ignition slot.

If the key starts the car, the IR led does work, also the coil at the key that takes power from the ignition slot works. Seems your button switches work if you can see the red indicator coming on from each button.

Even if the previous messages talk about FM radio issues and operating central locking via the IR sensors at the door handles, you do not mention anything about those. Better to have the full background to encourage proper replies and to avoid unrelated discussions.

 

[Bemmy]

Thanks for the prompt

The "sync" instructions were: insert key in ignition and remove within 10 seconds, hold the lock button and press the unlock button 5 times then press the boot unlock button.
Using the fob pointing at the sensor on the car door handle and pushing the unlock button doesn't unlock the car.
FM reception is normal.
The car still starts using the fob.
I do not have another fob to test.

When testing this evening I noticed that the red LED on the fob is no longer flashing when the buttons are pressed...........new fob I guess?

 

[MrGreedy]

I had a w203. Radio got gradually worse after I bought it. Then the key fob range got gradually worse, until I was left having to open the car with the IR remote pointing at the door handle.

It was the coupe. After stripping the rear window trim, I was able to find the connection between the antenna (in the glass) and the wires back to the car. It's a flat, black plastic component about 15mm x 100mm (from memory) that was I assume originally glued to the glass and making contact with the antenna. Whilst pushing the black component tight against the inside surface of the glass, hey presto full radio reception and key fob working at Long distance. I used a drip of epoxy and propped some timber in the open boot to apply pressure as it dried. Radio wasn't perfect, but the key was.

It's pretty easy to remove the trim and have a check on this operation. Left hand UK passenger side of the car for me. Probably no more than 30-60 minutes.

I would say it's a free check, but the w203 is old, and expect to break a few clips on the trim, so you might need to buy new ones from Merc. One tip I didn't know about. Give the plastic a good warning with the hair dryer on a warm day. It might take the brittle edge off the plastic and avoid snapping the clips. Worth a shot I say to rule in or out.

 

[oldguy57]

I had a w203. Radio got gradually worse after I bought it. Then the key fob range got gradually worse, until I was left having to open the car with the IR remote pointing at the door handle.

It was the coupe. After stripping the rear window trim, I was able to find the connection between the antenna (in the glass) and the wires back to the car. It's a flat, black plastic component about 15mm x 100mm (from memory) that was I assume originally glued to the glass and making contact with the antenna. Whilst pushing the black component tight against the inside surface of the glass, hey presto full radio reception and key fob working at Long distance. I used a drip of epoxy and propped some timber in the open boot to apply pressure as it dried. Radio wasn't perfect, but the key was.

It's pretty easy to remove the trim and have a check on this operation. Left hand UK passenger side of the car for me. Probably no more than 30-60 minutes.

I would say it's a free check, but the w203 is old, and expect to break a few clips on the trim, so you might need to buy new ones from Merc. One tip I didn't know about. Give the plastic a good warning with the hair dryer on a warm day. It might take the brittle edge off the plastic and avoid snapping the clips. Worth a shot I say to rule in or out.

That's a great bit of diagnosis and a cheap fix!