I have a 2002 Trailblazer LTZ and I cannot get the 4wheel drive to engage. It won't go into 4hi or 4low. When i move the switch to any position nothing seems to happen. I tried A4wd and 4hi while driving and 4low while in neutral but it just stays in 2wheel. Is this something as simple as the switch or do I have a major task in front of me?