p0420 came up

[corvairbob]

last time i posted on codes i had 3 codes p0030 p0130 p0135 all related to the 02 sensor. so i changed the upstream sensor. today the p0420 came up for cat efficiency. i changed out the front 02 sensor so now it looks like i may have to change out the rear. i'm going to run the car and take a temp reading on the cat front and back plus look at the 02 readings to see what they say and post those numbers. maybe they may tell something someone can help with if i don't see it. the car has 125k on it no oil use no leaded gas outside of a evap issue due to a broken wire all has been working fine. i guess the cat may be going bad but i'm leaning to a rear 02 sensor for starters and the mileage may be telling me it is time. and i had to change out the front one already. thanks.

 

[corvairbob]

ok update i changed out teh rear 02 sensor and now i will see if anything changes. i did notice the sensor runs more steady now and it is running around .6 to .7 volts if the cat is good this may go down as the cat gets a chance to burn off the junk. but with this time is going to be the factor as if the sensor was not the real issue then it may return.