Yellow Triangle with !
 

Recently, the yellow triangle with an exclamation point light will flash while I'm driving and I lose power. I can't accelerate at all. This has happened on the highway and has put me in a dangerous spot. When the flashing stops, it works normally again. I have a 1999 ML 320 with well over 253,000 miles on it. Any ideas on what's going on before I put it in the shop? Thanks!

Sounds like traction control or limp home mode. When it happens, try turning off the car and restarting.

If it recovers by itself, without having to turn ignition off, then it is most likely Not in limp home mode. Sounds more like one of the wheel speed sensors is failing.
Mike

i have the same problem, like you have a blow-out and a stalling engine all at the same time. used to be able to drive through it. now i have to pull over and turn it off and restart and the BAS ESP light stays on till i let it set overnight and it goes back off. then i get to wonder when it's going to happen again, it's going to get me rearended.

Triangle Flashing
 

I completely agree with Mike's ML above. I had exactly the issue you are describing on my 1999 ML430 with 190,000. Replaced front driver's side wheel speed sensor and problem is done .... 10,000 miles ago, no re-occurance. The problem generated lots of codes suggesting lateral sensor and other expensive sensors but once the wheel speed sensor was replaced, no other codes are being generated.

The sensor was new and pretty inexpensive on ebay. I don't recall it being a difficult job to do.

i've been turning the esp off and it doesn't do it, so i'm guessing wheel speed sensor over brake light switch. my brake lights seem to be working fine and i get no abs warn light.

Wheel Speed Sensor
 

Now you need to figure out which wheel. If you can have the codes pulled, I would ignore all the C codes that deal with steering (C1140) and Yaw/lateral accel or Rotary (C1120), brake switch (C1200), ESP module (C1000), C1140 or C1142 for lateral, etc.

Concentrate for example on a C1100 which will be left (US Driver's side) front, C1101 will be front right. I paid $35 for new genuine MB part on ebay, July 2012 from seller nomocarparts. It was an easy install.

If you're lucky, you might also have a P1605 code thrown ... I believe it confirmed speed sensor in my case.

Share your success with us if you're successful. Good luck.