Ok so I have a 99 limited with 180k. I was hit with the dreaded p0420 2 weeks ago. I replaced the rear o2 and after 2 weeks the light is back. My buddy is sending me his urd simulator to try. My question is does the simulator only affect the rear o2's? Plus the cats? Or does it fool the whole system that throws that code? Thanks for any help!!
P0420 URD simulator help needed
- Thread starter Dkemp340
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TheDurk
Elite Member
It only affects the rear O2, but that is the primary input to the Catalyst check. The front O2 is important, but if it is sub-par, it will usually throw other codes as well. The Catalyst checker works by comparing the two exhaust sensors under various use scenarios.
Thanks for the info. I thought the new o2 fixed it but I was incorrect. I'm hoping if I use the simulator it'll show me it's the cats if I drive it a while with it hooked up.
TheDurk
Elite Member
Not so fast. Let's say it's an exhaust leak. The URD sim could well override that and clear the code. Now you'll go buying new cats when it could have been a 4$ gasket.
So theres good news there too. I have a new set of high flow Evan Fischer cats that I got when I bought it. I was just gonna wait till I needed them before having them welded in. That'swhy I was wondering if the simulator overrides the whole code or just the cats. That way I could tell if it was a dead cat.
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Renegade_Medic
New member
You can run no cat and as long as the sensor is still kind of working and in the exhaust, the URD sim will work as far as the computer knows.
TheDurk
Elite Member
I'm not so sure. I put in a sim while I had a leak and, while I never failed, I never got a "Ready". It just sat "Not Ready" for months. Eventually, I found the leak, and it passed. Then I pulled the sim and it still passed.
Did it still throw a code with the sim?
TheDurk
Elite Member
As I said, no code, but it never went to Ready on the Catalyst Test.
