Mercedes-Benz CLK-Class Owner's Manual page 339

Practical advice
Troubleshooting
Problem
The key cannot be turned in the ignition
lock.
336
Possible cause/consequence
The on-board voltage is too low.
Suggested solutions
Switch off consumers that are not re-
quired, e.g. seat heating or interior light-
ing, and try to turn the key again.
If this does not work:
Check the starter battery and charge it
if necessary.
or
The vehicle may be jump-started
( page 379).
or
Consult a qualified specialist workshop,
e.g. a Mercedes-Benz Service Centre.