CEL and code PO420 (1 Viewer)

[MC80]

I have a 96 and the CEL light is on and reads out code PO420. I took it to the dealership and they hooked a scope up to both O2 sensors and they told me both sensors were outputting the same signal signifing the Cats were bad. The truck has 116k miles and is clean, so I have a hard time believing BOTH Cats are bad. Has anyone had their Cats fail with that low of miles? Before I replace the Cats, I'd like to be sure they are bad. I'm thinking about having the emissions tested and, if I understand this correctly, if the cats are bad I'm going to fail emissions at an idle AND at a faster rpm. If the O2 sensors are bad and the cats are good, I should pass emissions at an idle, but might fail at the faster rpm. I guess I'm wondering if the O2 sensor was bad and the motor was running on the rich side(because of the open loop diagnostic), would a good working cat clean up the exhaust enough to pass an emission test? If not, a failed test won't really tell me which part is bad. Any ideas?

 

[toddslater]

Disconnect the battery for 5-10 min to reset the ecu. If the CEL comes back on, I think your looking at following the advice contained in this thread https://forum.ih8mud.com/showthread.php?t=2211&highlight=P0420