ESP, ABS & Limp Mode
 

Hi,
I have a 2002 Audi A4 3.0 Quattro that used to go into limp mode sporadically right after the ABS & ESP lights come on, but appears to be rather consistent these days. The codes that my reader pulls up are P0638, P0222, and P0121. My drive home from work goes into limp mode almost every day after the coolant light flashes followed by ESP & ABS then limp mode or more frequently ESP & ABS then limp mode. There has to be some correlation between the length of time driven because my car doesn't go into limp mode on the way to work since the drive is half the time compared to the drive home. There are also certain locations of the interstate that trigger the ESP & ABS light to consistently come on. The other times ESP & ABS lights trigger limp mode is with wide turns or windy roads. My mechanic cannot find the problem because you typically have to be in the car for 50+ minutes for the lights to come on. I have another mechanic that can look at it, but wanted to get your opinions with regard to the estimated damage ($) and/or possible solution for fixing my limp mode problem.

Thanks