One problem related to gas recirculation valve (egr valve) has been reported for the 2001 GMC Sierra. The most recently reported issues are listed below.
My vehicle taps very loud when I first crank cold engine. Dealer says this is carbon build-up because of new emmisions regulations and wont harm engine. My dealer says they can perform a treatment for approx. $100. 00 that will correct but needs to be done every 20000 miles. My vehicle is still under new car warranty but they said this service is not covered. I have several friend experiencing same problem. I feel this is a defect in the new general motors engine. Thanks.