p0420

[jerryjer8]

i have a 96 outback legacy with 2.5L. ive been getting a p0420 code lately, about a month ago i had to change the back pressure transducer going into the egr, and since then i get a p0420 bank 1, and a second code for the same exact thing that says pending, i recently bought this car a few months ago so i dont know how long the egr wasnt working correctly, my thinking is telling me that if it was running richer becuase the egr was not working correctly, then maybe it gunked up the front o2? does anyone else believe my thinking is correct, i warmed the car up earlier and got it good and hot went to pull the front o2 and look at it and it is very very tight, while the back o2 felt it was very easy to come loose, i did not pull either out to look at but im thinking that maybe the front o2 is stuck open and not allowing it to come out easily. should i just start by buying a new o2 for the front and start there.

 

off my code reader i get

 

p0420 1 of 2

catalyst efficiency

below threshold

(bank 1)

 

p0420 2 of 2

pending

catalyst efficiency

below threshold

(bank 1)

[Legacy777]

When you replaced the pressure tranducer, did you replace it with a Subaru OEM part, or one from a parts store?

 

How many miles are on the car? If the mileage is high, it's possible the O2 sensor may not be working correctly, and once you fixed the EGR, the ECU picked up on this.

 

However, as you mentioned, the EGR may also have some carbon build up that may be causing you issues.