Help with P0420 - Toyota Nation Forum : Toyota Car and Truck Forums

hky · 09-29-2011, 03:32 AM

Hello,

I have a 1996 four cylinder Camry with 200k miles. The check engine light came on with the P0420 code. The light had been on for a while and after repeated reset it seems the code only comes up in the summer when the outside temperature is hot. I am a little puzzled by this since the catalytic converter is supposed to be more efficient when hot.

The problem initially came up after the radiater was changed. I tried to look for possible leaks. At first I tightened the valve cover nutz as there was some indication of oil leak (no appraent leaks with visible hoses). This initially helped but the light came back on after a few months (I think I have done as much as possible with the tightening of the valve cover). Since the problem goes away in cooler seasons my guess is there is nothing wrong with the oxygen sensors and catalytic converter. Any suggestions on how to trouble shoot the problem would be very much appreciated. Thank you.

csaxon · 09-29-2011, 09:07 AM

Look for exhaust leaks especially around the flex pipe. If the o2 sensors are original with 200k then you should consider replacing them. They lose efficiency around 125k and your gas mileage will suffer. This sensor is the usual P0420 culprit and is easy to replace.

Pvt-Public · 09-29-2011, 11:53 AM

My experience with the dreaded P0420 was that replacing both O2 sensors (actually an A/F sensor for the front, mine is a Cali. spec model) has kept the P0420 at bay for over a year now. Provided that there are no leaks in the exhaust system and the Cat is not actually bad. Just as a side note I don't see how the valve cover gasket could have anything do do with it at all.

***JohnGD*** · 09-29-2011, 05:15 PM

The 96 uses unheated thimble sensors. After 200K miles, if there is no exhaust leak and the engine is well tuned, then change the sensors first.

hky · 09-30-2011, 06:30 AM

Thank you all for the feedback. I have noticed the fuel efficiency has been going down; I was wondering if that is related to the P0420 since as I understood it the input from the sensors is no longer used. Any thoughts on why the code is not triggered in Fall-Winter-Spring?