Late 02 CLK320 W209 Central locking intermittent. As of today not working.

[Michaeltyas]

Just bought low mileage 02 CLK320 W209 and central locking very intermittent. Two of the chrome keys I have show no sign of life, but one black key I have shows red light when buttons pressed, all have new batteries. The black key works for a couple of days, but like now has just stopped working altogether, still showing red light when button pressed.
Central locking works from the switch on the dash and I've checked fuse No.8, which I believe is for the central locking and that is fine.
Any help gratefully accepted.
Also if I can central lock with the key fob, yet it won't unlock, if I use the manual key to unlock, can I turn off the alarm by turning on the ignition.
Thanks.

 

[AltonAnt]

Does it lock/unlock if you use the ir sensor on the door handle rather than rf? This would indicate the antenna amp is kaput.

 

[Michaeltyas]

Does it lock/unlock if you use the ir sensor on the door handle rather than rf? This would indicate the antenna amp is kaput.

I may have fixed it by resetting the key to factory settings, holding down lock and unlock until the LED flashes twice. It locked it last night, will have to see if it opens it today.

 

[Michaeltyas]

I may have fixed it by resetting the key to factory settings, holding down lock and unlock until the LED flashes twice. It locked it last night, will have to see if it opens it today.

I haven't fixed it. After the key reset it unlocked everything last night, but back to normal today, it will not work again.

 

[Michaeltyas]

Does it lock/unlock if you use the ir sensor on the door handle rather than rf? This would indicate the antenna amp is kaput.

Hi AltonAnt. It will not lock or unlock by rf or ir. so still baffled.