Continuing to crank but not start 2008 Pontiac Grand Prix

Pontiac Grand Prix

Suddenly car will crank just fine but not start. At the same time the car started continuing to crank after key is turned back. Where should I start troubleshooting?

Start your troubleshooting with reviewing the wiring diagram for the engine starting system. This will give you an idea of all the electronic components involved.  After reviewing the diagram myself the first thing that I see that could cause the issue would be the relays. Your engines starting system has two separate relays involved. The IGN1 Relay and the Crank Relay. Relays have a tendency to get stuck or stick in one position when they go bad. I am thinking that is what is taking place here.

Engine Starting Wiring Diagram