My 2010 ML350 W164 doesn't open or close easily using (both) the remote keys. Sometimes I need to press the open or close button for 10-20 times walking around the car and it unlocks or locks after a while. But after riding the car for some time it is ok again and the carlock reacts like it should be...
The car always does crank normally so main battery isn't dead. The battery in the keyfob is new.
So what could be the issue? 🤔
Auxiliary battery?
Antenna problem?
Fuse or SAM?
Any insights?

 

How are the contacts in the key fob? A fresh, soft pencil eraser can clean them up nicely.

 

One of my keys has just came back from a "refurbish job" and was tested 100% ok. The other key always worked fine, now bot have the same problem so logic dictates that the problem is probably on the car side.

 

How old is the main battery? What does the voltage with the key on but engine off look like?

 

Main battery is fine I think. It starts ok and the voltage is 12.7V when the engine is off.

 

Mine does that in certain locations where there is a heap of radio interference. Is yours location specific when acting up or does it do it everywhere?

 

Pretty much everywhere, but especially after 12+ hour parking the car (anywhere). When the car is warm (charged?) I have no problems.

 

Update:
Replaced the Auxiliary battery and the remote key works perfect again. So that small aux battery was bad... but I didn't get any warning on the dashboard and not in the diagnostic device.
The process to get to that battery (under the passenger seat behind the main battery) was a pain in the ***. To remove the main was heavy! literally.. 24kg to lift out of the car in an impossible position. But I managed.
job done.

 

Aaaaannndd... The problem is back again.
after working for an hour or two I'm back at square one.
The search continues.

 

Scan codes and report back

Check for water infiltration in the usual places, rear tire well highest on the list.

 

I found out that:
A) my recently refurbished Fob completely stopped working, again.
B) my spare fob had a flat battery although I recently replaced it
All at the same time. What are the odds?

At least all is working again with one key.