W210 key won't turn

[CharlesL]

Key will not turn at all and I've read multiple suggestions but many were 10 plus years ago, and not verified fixes.
Steering wheel is not locked, gearshift is.
Also, the car alarm has acted funny lately; intermittently going off at night for no reason.
Before I go into the EIS, could the alarm be preventing the key to turn?

 

[brandwooddixon]

In a word unlikely.
The alarm going off is probably due to battery leakage within the alarm siren. The car can run without issue with the siren removed.
Have you ruled out key batteries or the key itself - dropping them can stop them working as the antenna breaks off by replacing the batteries and trying a spare key?

 

[mersum1es]

Yep, key battery has nothing to do when key inserted to slot, battery is only for remote FM and IR sender. Key has simple coil inside, which inducts current and activates electronic when inserted to EIS, it is common fault that soldering of coil is broken, Search more for info.

And yes, alarm battery can draw main battery too. Did you measure battery voltage?

 

[CharlesL]

In a word unlikely.
The alarm going off is probably due to battery leakage within the alarm siren. The car can run without issue with the siren removed.
Have you ruled out key batteries or the key itself - dropping them can stop them working as the antenna breaks off by replacing the batteries and trying a spare key?

I've ruled out key batteries; replaced them. Ordered new fob case and going to put the chip in it and cross my fingers. I only have the 1 key.