I have a a 2006 xc90 4.4 155k that started throwing a p0420 code. I'm trying to go down the list and diagnose before I start throwing parts at it. It doesn't have any exhaust leaks I have found. The converters appear to be working fine...Cold start Bank 1-2 sensor 1 585 C, Bank 1-2 sensor 2 460 C. O2 Sensors Bank 1-2 Sensor 1 .01-.05mA, Bank 1-2 sensor 2 fluctuates evenly between the 2 from .15A-.85A. Do these look out of the ordinary at all? Is there anything else I should check...I'm guessing the o2 sensors are original and probably overdue for replacement.

 

Not quite sure what all your numbers are. - What are you measuring amps with? and what is 585C?

Older O2 sensors you could easily measure the voltage output, newer wide band sensors not so much. But If you could measure the output from a rear sensor with a perfectly working fuel injection system, front sensor and cat converter, the reading would be stable and close to 0.

HC, Hydrocarbons, CO, carbon monoxide, O2 and nitrous oxide are the 4 byproducts of combustion. The front part of the cat chemically takes apart the HC, CO, and O2 - and turns them into H2O and CO2 - So if everything works perfectly when the rear O2 sensor gets to sniff - there's very little O2 left to measure so very little voltage.

Your po420 code is a cat efficiency code - your .14a-.85a reading (whatever that is ) on a rear sensor should be stable - that could be telling you the cat is not working (converting hc, co, o2 to h2o, co2). A voltage reading from a front sensor fluctuates like that and the rear just follows if the cat is not working.

You could try a (or 2 for a v-8) oxygen sensor extender - people use them to fool the ECU when cat converters are not working. Or they have a tune or other aftermarket stuff that changes the mixture. The rear sensors are taken out of the direct exhaust stream and are less likely to notice a fluctuating rear sensor.

It can get mighty expensive chasing a cat efficiency code on a V-8, 4 O2 sensors then new exhaust manifolds w/ integrated converters!
Is an emission inspection required where the car is registered?

 

I hear you on the cost of it all...800-1500 for headers/cats, 120-600 for the mid pipe cats and anywhere from 30-150 per o2 sensor, and that's without labor (even though I'd probably do it myself) I got my amperage measurement from my scan tool...it has live data (pretty basic) it doesn't have waveform graphs which would help confirm o2 sensors working and cats status. I reset the CEL last night, it still only had the p0420 and no other codes. I've driven it around 40 miles since the reset and the light hasn't come back on yet...although it's done this a few times over the last couple months so I expect it will eventually.

Lucky for me I'm in Oregon so no emissions testing...but CELs bug the heck out of me and I don't like doing jerry rig fixes. I've read about the o2 extender to trick the ECU

Any thoughts on the cheap/off brand replacement components? EX: the ebay replacement mid/cats for $120.00, or non bosch/denso o2 sensors that are only 15-30$ each

It's tempting to try them but I usually get burned on aftermarket or off brand electronics and replacement parts.

 

Yes that CEL is a pain and using cheap aftermarket parts is even worse. (because you may be throwing your $$$ away on stuff that won't work and you can't return it, but someones wallet gets bigger at your expense.)

Factory cats are expensive because Platinum, rhodium and palladium are used in them to make the process work. Those elements are expensive. Aftermarket converters just don't have much of that stuff in them - so they don't last long.

You have a 14 year old car - put some extenders in it and hope that will stop the efficiency code. You don't have to have cat converters for the car to run. Save your $ for things that are more critical. (house, next car, 401k, wife, kids college, etc)

 

I get this code and after driving for extended times the car starts to jerk and fuel system goes haywire.Ive done a live test and even the fuel pressure drops,map sensor reading changes and everything in between.I suspect the bank 1 upstream sensor might be faulty?Am I correct in my assesment?
Btw I drive a 2008 xc90 v8 sport with cat back exhaust system.

 

No.

That code comes from the ECU comparing the values from the front and rear sensors - There is oxygen left in the exhaust stream after combustion (by design) that is measured by the front sensor - then the converter uses that oxygen during the catalytic process - after which the rear sensor should report that there is almost no oxygen after the catalytic process. That code means there is too much oxygen left usually due to a converter that's not converting CO and HC into CO2 and H2O as it should. Both o2 sensors are self tested before the converter - so I would think you would have a sensor code if one were bad.

The front sensor can change the mixture - but only very slightly, not enough to make the car run bad.

What scan tool are you using?