Hello, 3 weeks ago I bought an 04 4runner with 95k. 1 week ago the check engine light came on with a P0420. I took it to the dealer and they were nice and put in a new cat for free (i know not something stealerships usually do) 50 miles later the light came on again. I took it back only to find out they replace THE WRONG ONE. I am waiting for a call from the service manager to see if they will do another one for free ( I have my doubts, even though it was there mistake) I did not relazie there were 4 cats on a 6 cylnider enginge. Seems a bit excessive. Anyone have any suggestions as to what I should do if they don't replace the other cat? I heard alot of times it can be the sensor throwing a bad reading. Any help would be appreciated. Sorry for the novel.

On the 1grfe we have four cats and four sensors. The four sensors only monitor the health of the front two cats which are located on the exhaust manifolds. I'm guessing the reason they didn't replace those is that they are a pita to remove and install. The sensors can go bad as well because of age, heat, etc. It could even the wiring though I have only seen that once when I helped installed a set of JBA headers on a buddies taco which had seen alot of off roading. If you just need a O2 sensor look up Gadget at URD as he sells them and might hook you up. If its the cat they might either hack off the old one and weld a new one in place or order a whole new exhaust manifold as its one piece. If you need those I have two I'm not using. Those are really your options unless you want to go exploring the in the performance world.

See my post in this thread:



IF you are using your 4Runner for offroad use only, those devices bypass the second set of sensors (O2 sensors) and make your computer happy.

That way your check engine light only comes on if some ELSE is wrong, not just due to emissions. ;)