my 2002 pont. grand prix won;t drop into passing gear when needed?It sifts ok otherwise.A mechanic checked it and no codes showed up. 3 months ago the service engine light came on and a GM dealer checked it and said the catalic converter needed replacing but didn't have one in stock,the light went out so I didn't change it.The trans.shifted OK until this 2 or 3 wks.The fluid level is OK.What is the problem?

Ernie Moorhead, January 2012

Your cat converter could be nearly pluged.Check the RPM when trans.should be down shifting to passing gear.Park car and depress gas pedal to floor momentarily,engine should rev to max RPM.Engine may faulter due to high back pressure from plugage of converter. If it does't reach max RPM,it's the above problem.

Had the same problem, January 2012