'Service engine soon' light on in a 97 Pontiac Grand Prix?

I gave it a tune up, replaced the EGR, changed the PVC, replaced the catalytic converter, changed the upstream oxygen sensor and checked all the fuses. Yet this stubborn light refuses to go off.



I've heard that it could be the gas cap; it passed the AIM check on that particular test. I've heard it could be the fuel injection, and I've given it fuel injector cleaner. The light has stayed on.



I've gotten the light reset. It comes back on. Same code everytime.

P420. Catalytic performing below threshold bank #1.



Does anybody know how to fix this?'Service engine soon' light on in a 97 Pontiac Grand Prix?2 things downstream o2 sensor also are you loosing antifreeze?? intake manifold gasket'Service engine soon' light on in a 97 Pontiac Grand Prix?on an obd2 system that code means that the pre and post cat o2 sensors are having a very similar voltage pattern. the computer sees the4 similar voltages as a sign that the cat it self is not doing its job. i do not see that a fuel injection problem could be causing this unless the4 computer is not altering the fuel mixture. in order for a cat to work it has to see a rich/lean/rich/lean/situation. this allows the catalyst to absorb and use O2, with out this it cannot work. 'Service engine soon' light on in a 97 Pontiac Grand Prix?Catalyst below threshold can mean a couple things. The ECU is reading the upstream and downstream O2 sensors and looking for a specific difference between the two. When it sees nearly the same readings on both sensors, The ECU throws out that code. This may be a bad cat, but it could also mean bad O2 sensor(s). Find a good Tech to actually diagnose this properly. It's obvious that you have thrown a bunch of money at this engine light, starting from scratch with a GOOD tech will be money well spent.'Service engine soon' light on in a 97 Pontiac Grand Prix?thought about calling the parts department of your local dealer and ask them what the code means? Or how about calling an Auto parts store? Often times if you look hard enough, you can find a knowledgeable person that will give you some free advise and save you from expensive parts guessing.'Service engine soon' light on in a 97 Pontiac Grand Prix?The O2 sensor downstream from the cat would cause this signal. Thats the one that checks to see if the cat is doing its thing. Since you changed so much stuff already, might as well get that one too. Good luck.'Service engine soon' light on in a 97 Pontiac Grand Prix?You didn't mention oil change.

I've seen cars do that when the oil is low or dirty



could also be crappy gas or clogged fuel filter'Service engine soon' light on in a 97 Pontiac Grand Prix?best advice bring it into the shop and find out whats wrong and tell them what you did with the PVc thing