I'm not at all familiar with the 2.7 engine, Max, but the belt tensioner will only release the tension on your serpentine belt when pulled in the correct direction. You've got a 50/50 chance of pushing it or pulling it the correct direction. Just get a wrench on the center bolt and pull it towards the front of the car. If it doesn't release the tension, then try pusing it towards the firewall. I'm no mechanic, but that's how I find out which way releases the tension on the cars I own.