Question

Would a P0420 keep my 2002 Pontiac Firebird from starting it will turn over but not start?

Answer 1

This code rarely causes a no start condition. If it is completely plugged up it might, otherwise no. I would check for fuel and spark at the culprit. You can also pull the O2 sensor out that is ahead of the converter to see if it will then start. This will give the exhaust a place to go if it is the problem.