We recently purchased a used 2001 GMC Jimmy 4wd and the 4wd was not engaging we had to take it th GMC because no one else could do the diagnostic test. Our ABS light is also on, GMC charged us a little over 800.00 to put in a acuater and then a week or so later it started with a loud whistling noise and then when we tried to put it in 4hi the lights kept blinking back in forth from 2hi to 4hi. We took it back to GMC who said that it was the switch and the transfer case fluid was leaking sucked up into all the ac and heating lines. They want to charge us over 1,400 now to fix it which we cant. Anyway is there anyone out there familiar with the 2001 4wd problems and how I myself might be able to repair the fluid in the lines. I already put the switch on. Nothing but a money pit so far. I wish I had never bought it. Please help at my wits end and cant trust nor afford GMC anymore.Thanks