2000 Toyota Avalon PO420 code Bank 1

1989CHEVY

MEMBER
2000 TOYOTA AVALON
175,000 MILES

I have replaced all the cat's (3) and the same code still comes up. I will be checking for leaks, but I dont think that is it. Took it to the dealership because I have tried everything I know. Dealership said sencors or leak or computer. They want 110 dollars just to tell me what it is. I did check the temps of the cats before replaceing and they where bad. The sencors bank one and two are reading the same and the one down futherest down line is very low and dose not maintain a constant. Any other ideas?

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,179 POSTS

I hate to say it, but they are right. It could be any of the things they mentioned. I wouldn't think computer first, but rather the O2 sensor. To add to the list, it could be the result of wiring to the sensor, a faulty temp sensor, a leak in the exhaust system, a leaky fuel injector, fuel pressure that is too high. The list goes on.

Some things to check:

Make sure there are no exhaust leaks
Scan the sensor to see if it is working properly (NOTE: The sensor in front of the converter usually will fluctuate where as the one behind the converter will be more steady.
Make sure that both down stream and up stream sensors are not giving the same readings. That can also cause a PO420 code.