CLK stuck in low gear

My CLK went into "limp home" mode a few days ago, right after going
through an automatic car wash followed by a thorough hand-wash.  It
showed various alerts on the electronic display, including the "check
engine" light.  I was able to get it home by driving slowly (it would not go
above 25 mph), and I let it sit without driving or starting it the rest of that
day.  The next day, after reading about this kind of thing online, I decided to
disconnect the battery for 24 hours and then recharge and reconnect it.  I
also added some oil since I had gotten a couple of display alerts about low
oil recently.  But then when I started it up and took it for a quick test drive
today, it still wouldn't shift out of low gear.  The check-engine light is no
longer illuminated, but now I'm getting alerts about the BAS and the ESP.  
Looking for any ideas about possible causes and solutions before I take it
into the repair shop.  I'd hate to spend a bunch of money on a costly repair,
considering I was only planning to keep this car another 3-4 months before
replacing it with something newer.