1996 camry P0420 check engine light

[prof]

Hi folks, first post here and 6 month toyota owner.

I purchased for my son a 96 Camry LE 4 cylinder 140,000 miles. I had the timing belt and water pump replaced two weeks ago and then this week the check engine light illuminated with the code P0420, cataletic converter not operating efficiently. Before I start replacing O2 sensors or a cataletic converter, Im trying to figure out what may cause the converter to not work properly. Are cataletic converters high failure items on this model camry? If not, what are some areas that I should focus attention at? Some ideas that come to mind

1. Incorrect ignition timing. The car has started pinging or knocking when the accelerator is floored and the engine is under load. It didnt do this prior to the timing belt change. Not sure if incorrect timing and impropper combustion process would foul out the converter.

2. Impending head gasket failure. The coolant in the overflow tank, which was replaced two weeks ago is dark in color already. The engine does not steam out the exhaust pipe, no coolant on the oil dipstick nor does the radiator blow out coolant when you start the engine but I do know that coolant into the combustion chamber will destroy the cat and O2 sensors. I know two people with this model camry that had head gasket failures between 100,000 - 150,000 miles. Are head gaskets high failure items?

Any help appreciated.

Steve

[avalon2000]

I had a 99 Camry for 4-5 years. I went througth the "check engin" headach for years. A local garage said it was O2 sensors, and offered me to replace both for $600. I didn't want to spend the money. I was glad that I didnn't. It turned out it was a hole in the exhaust pipe. Eventually, I had the rusted exhaust system replaced and the light went away, for 1 year. Later on the light came back on again. I replaced the upper o2 sensor (about $100 cost) myself and fixed the problem. The upper o2 sensor is really easy to replace. After replacing it, you may go to Autozone and ask them to clear off the error code ( Or purchase a code reader for $40 online, like I did, and clear it yourself.)... Hope this helps... Good luck.

[B-R-T]

1. Incorrect ignition timing. The car has started pinging or knocking when the accelerator is floored and the engine is under load. It didnt do this prior to the timing belt change. Not sure if incorrect timing and impropper combustion process would foul out the converter.

ignition timing by itself can't cause knocking. check spark plugs. if they show signs of extreme heat, put the ones, that are one step colder.

higher gas grade will help too.

about the cat..

cat's lifespan is about 95k miles. after that it could be useless.

[B-R-T]

on the other hand.. valve timing can cause knocking. check the alingment of crank ant cam gears.