6month Toyota owner. I have a 1996 camry 140,000 miles. Had timing belt and water pump replaced two weeks ago. Last week, the check engine light illuminated P0420 code cataletic converter below efficiency. Before I go replacing O2 sensors and the cat, I'm trying to figure out what what has caused the cat to potentally fail.

1. Incorrect ignition timing from timing belt change. Car runs about the same as before except it pings or knocs when the accelerator is floored under a load, didnt do that before. Would incorrect ignition timing and incomplete combustion foul the converter?

2. Potential head gasket failure. Coolant in overflow resevoir is dark colored at two weeks old. No coolant in oil, no steaming out exhaust pipe though. Two family members with 4 cylinder camrys had head gasket failure between 100,000 - 150,000 miles. I know coolant in exhaust will ruin cat.

Any help appreciated.
Steve

 

its more likely the cat just getting old...reset the cel by pulling the efi fuse for 5 sec...lets see if the light will come back on... if it does you'll need to test the cat by monitoring the sub o2 sensor...

 

If it is a blown headgasket check the right rear area of the engine for moisture. This is a problem area in some later model camrys. If this is the problem your fluid level should have dropped and if you turn your heater on there will be only cold air.

 

The engine should not knock under load, perhaps the timing if off. Or try higher octane fuel.