P0430 P0420 Trouble Code Investigation using Ultragauge

I know the P0420/P0430 CEL trouble code has been discussed before but I didn't see a thread with this specific info so....

2005 DCSB A/T
110k miles

Last week the CEL popped on, have never seen it it my ownership of the truck. A scan revealed P0430 "Catalyst system efficiency below threshold - bank 2". I tried the usual, clean MAF, check spark plugs (the were changed 10k miles ago), ran some fuel system cleaner and a tank of ethanol free high octane through. No dice, code still triggers.

So I set my Ultagauge up to measure the O2 sensors before and after the catalytic converter. Now the Ultragauge is measuring temperature I believe, which maybe isn't ideal however. What I found is that the sensor before the cat (sensor 1) always reads 150-200 degrees higher than the sensor after the cat (sensor 2) which makes sense. So as I'm driving the Ultragauge alarm sounds that a pending trouble code was just thrown, I look at the O2 readings and the temperature of the two sensors is virtually identical. Within 30sec sensor 2 returns to being 150-200 degrees cooler.

I've now verified this a couple times, 99.999% of the time there is a 150-200 degree temperature differential between the sensors and no trouble codes. That brief moment where it reads the temps as being the same, bingo trouble code P0430.

So the question is, faulty O2 sensor, faulty cat, faulty air pump? Thoughts? Does anyone know if the drivers side O2 sensor is interchangeable with the passenger side, I know the sensors are most likely the same but what about the connector? My first thought is to swap sensors and see if I can swap to a P0420 code and confirm the sensor is at fault. Now there is no difference in drivability and I've noticed no decrease in gas mileage, also I have no need to pass any type of emissions testing so this isn't a major issue for me, more of an annoyance and an interesting opportunity to troubleshoot something.

 

hate to bring up a dead thread but what ever happened with this?