Hey everyone,

I first got a p0420 code for "Catalyst Efficieny Below Threshold - Bank 1", or something.

I had the driver's side cat replaced, but p0420 came up again. The shop found 2 bad o2 sensors, and replaced both.

It was fine for about ~100 miles, then p0420 came up *again*.

If its not the cat, and its not the rear driver's side O2 sensor - it's gotta be the wiring right? This car I recently bought had a stereosystem in it (its pulled out now), and the rear left speaker is dead (well, woofer is fine, no signal though). There is also a small drain on the battery - when I shut off the car, the battery guage sits *right* above the orange area in the gauge. When I come back the next morning, the gauge shows voltage at slightly below the beginning of the orange area. Something seems to be draining the battery?

I'm planning on picking up a multimeter in an hour or two to confirm there is a draw on the battery - that way, I am hoping I can pull fuses, find what circuit is drawing the power, and perhaps, if I'm lucky, it'll be crossed with some o2 sensor wiring, or something.

I'm pulling out my hair, and I'm a bit dissapointed as this car is a recent purchase. Please help! I'd love to hear your advice, tips, or past related experiences with this sort of thing.. anyone have a p0420 which turned out to be the wiring, not the o2 or cat?

Thanks a million,

- Kyung

 

If it were wiring I would expect a code like 137 or 138, not a 420.

My first question is what brand O2 is it that appears to be giving the problem? Anything other than Standards which are made for GM, Delco and Delphi may be a problem. ie I could never get Bosch to work in my vehicles.

A couple of things to try. Unhook first the O2 on the problem side and then the O2 on the other side and see what code comes up then. Swap the O2s bank 1 to bank 2 to see if the problem stays or goes with the O2.

Try an inexspensive simulator like these http://www.o2sim.com/24803.html and see what the PCM does with that.

 

Thanks, speedy! You've helped me out several times back when I had the 95 z28 - I really appreciate all your help!

I'll try putting two O2 sensor simulators on the drivers/passenger side's rear O2 banks. I think what you said might be right on the dot - only the driver's side O2 was changed, so i wonder if there's a difference in readings between the new o2s on driver's side vs. the old o2s on the pass. side?

Well, once the O2 simms get here I should know.

Thanks!