P0420 during deep freezes

[utechtl]

Hi all.

Trying to figure out how to even start troubling shooting this. Owner before was meticulous about noting maintenance stuff and babied the car; sunday drive to church parked in a garage. Then when it got to me, it got the college kid treatment, parked out in in a lot during the worst Northern MN winters and that polar vortex last year.

Anyway, trying to figure out this out, I don't get the code during the summer months or if i have the car running and clear the code, shut it off and then restart it. IE it's warmed up. This leads me to suspect there's something going on related to expansion (I also think I read something somewhere re: intake manifold gasket leaking when cold)

The $06 pass except for the "Exhaust gas sensor bank 1- sensor 1" reads 8.0/9.0, minimum is suppose to be 10.0.

Any ideas on where to start troubleshooting? really don't want to through more parts at this than needed.

[zbyers]

P0420 typically means your converter is below efficieny thresholds. If you have a bluetooth code reader, hook it up and look at the o2 sensor graphs. If they make nice "waves" the o2 sensors are fine. It would then be your cat.

I see you have an '05...Magnaflow 99205HM is a great fit on all 03-08 FWD cars. Will not work on AWD as the exhaust is much smaller. I cannot confirm on the 09-10 Vibes of any trim level, as we no longer have any of those.

[utechtl]

So bought OBD Fusion (and they have IAPs?!) and took a look at my graph. I'm going to go out on a limb as and say that O2 sensor 1 is bad. Bank 1 sensor 1 was a flat line at 0V, Bank 1 sensor 2 was going between .1 and .5 V.

[jolt]

This may help. It shows the good and bad patterns and how the trace the cause down. After checking wiring and connections for the sensor output and heater, check for air leaks in the exhaust system.