What Scan Gauge did you buy ? I hope you bought one that records live data ? This is the one I've been using for 2 years now its paid for its self many times over. It also shows your fuel trim. And when a cell is triggered it will show you what caused it. ( don't go cheap on just a simple code reader, trust me I learned the hard way )
http://www.canobd2.com/Products/Tool...5fcd2d10756b95