I have a 2004 CLK320 which is not recognizing the keyless entry keys. The keys do work to start the car when inserted into the manual keyslot in the dashboard, but nothing else. The keys will not lock/unlock the car nor open the trunk. We did have a wicked cold spell of weather last week but we've had weather like that in the past. I've replaced the batteries in both keys and it made no difference. I've also checked the fuse with a DVM and it checks out OK. I'd greatly appreciate any ideas or input you may have as this is driving me nuts.
Thanks

 

When you say "keyless", do you have KeylessGo where you just touch the door handle to unlock, or do you mean just using RCL (Remote Central Locking) by pressing the button on the SmartKey? If it's standard RCL, then check to make sure the LED on the SmartKey blinks when you press its lock or unlock button for over 1 second. If not, the SmartKey is not transmitting. It could be defective, or your batteries may be bad, incorrectly installed, or the battery contacts may need to be cleaned.

If the LED does blink, then check fuse #8 on the rear SAM (in the trunk). If all of that is good, then RCL may have become de-synchronized. First, try to switch the keys from global to local unlocking - press and hold LOCK and UNLOCK on the fob for more than 5 seconds (observe the LED blink twice). Check the operation of the infrared transmitter by aiming it at a digital camera an pressing a button. Digital cameras will show infrared light as white so you'll know if that is working. If so, aim the key at the sensor on the door handle, about 6 inches away, press and hold unlock for two seconds, then immediately start the engine. Finally, try starting the engine, then as you turn it off, press and hold the UNLOCK button and keep it pressed fro five seconds as you remove the key from the ignition.

If none of this helps, then they keys have become desynchronized from the car and they will need to be replaced (or the EIS will need to be reprogrammed). And BTW, as you probably already know, the battery in the SmartKey is not used for starting - the EIS provides an inductive current to power the SmartKey's DAS circuitry.

 

I have similar issues with the smart key/keyfob. On the passenger door the smartkey doesn't work to lock or unlock the door. On the driver's side the smart key/keyfob does work. The smart key/keyfob works on the trunk just fine. The car starts just fine using the pushbutton start. Any suggestions would be greatly appreciated.

 

So you have KeylessGo and it doesn't work on the driver's door. It's one of two things that has failed - either the antenna on that door or the touch sensor on the handle. If the outside lock button on the door handle works, then it's the touch sensor. If not, then it's the antenna.

 

Keyless go is a common issue. Mine stopped working on my drivers side door a couple months ago. The sensor in the door handle went bad. Had to replace the handle but I bought it online, already painted for around $150 shipped. The good news is that its an easy DIY and you dont have to reprogram it since its just the sensor.

 

mine was giving me trouble and I did the resync. Still nothing but then I squeezed the handle a little bit closer the front of the handle and it worked. It was like the plastic was too flexible so it would bend but did not put pressure on the switch I guess. It was the Georgia heat softening up the plastic I think. Just my expierence.

 

The handle uses capacitive touch sensitivity and not pressure (like an iPhone screen). You should just be able to "wipe" the inside of the handle with your fingers without pulling on it and it will unlock the car. Like I said, when it acts up, see if the lock button works - if it does then it's the handle's sensor, if not, it's the antenna (assuming that the key works fine on the passenger side, trunk and starter).

 

THis may be true of later models, but not on CLKs. It is an actual lever you have to squeeze, and wiping it doesn't do anything.

 

Really? It's been a while since I've operated a KeylessGo MBZ - like years - so this was on older models. I was certain it was capacitive touch sensitive. Maybe it's just been so long that I don't remember correctly. I know our former Lexus was just touch, and a BMW and the current Jeep is, too. The Nissan Murano my wife had used a physical button (the same as the lock button on KeylessGo) which was awkward. The sensor being mounted behind the handle makes the most sense, and I jsut don't remember it requiring any pressure.

 

Yep, really. I double checked after you posted. It's a long black piece that fills most of the inside of the handle that moves when you pull on it. Same with the locking - the little button must be pressed, not just touched. Doesn't require much force, but some.

 

Dang! I'm going to have to make a trip to visit the dealership and verify this! Of course this is going to be a major ordeal - I will have to talk to some old friends, and maybe even have coffee... :-)