2015 XC70 P0420 with CAT pics, troubleshooting assist

Cmobile

Cmobile

Joined
May 5, 2012
Messages
324
Location
Arizona
Just bought a 2015 XC70 T6 w/ 3.0l turbo.

I pulled codes before I bought it, nothing active, pending or stored.

Drive 150 or so miles home, no issues. 2 days later, MIL on w/ P0420. Ran CataClean 2 times, Techron, clean MAF. Comes on every morning on my way to work.
Replaced upstream wideband 02 (mA always showed 1.0) now I get minor fluctuations for upstream, but the downstream will read about .5-6 for 5-20 seconds, then drop to .01, then up to .7, then repeat. Same at idle, 1500 RPM and 2500 RPM while parked (all accessory loads off)

I will be checking for exhaust leaks this weekend with The shop vac pressure method, using the discharge side of the vac.
When I replaced the upstream, I took pics with boroscope cam. (Not the highest quality unit, but functional)

Looks clean to me.

Didn't want to throw more parts at it until I have reasonable doubt, ( e.g. downstream 02)

Any thoughts on what elso to look at or test?
I don't have VIDA, just ELM BT reader.

Thanks

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Tried to post a short sreen video grab from mu phone using myOBDLink MX+ reader, but I'm not technically savvy enough. Says not supported
 
My guess is the original owner reset the codes prior to sale. Did you check to see if all the readiness monitors were set?

Either way - what does your long term fuel trim look like? Should be +/- 5% hopefully.

MAF should be about same number of grams / s as displacement - so in your case around 3.0 grams/s at idle.

If everything looks good I would run a bottle of kataclean through it. It won't "fix" it, but if the code goes away for a while its likely the CAT. Could also be a lazy rear 02 sensor. Could be a combination of things - old plugs, lazy 02 sensor, almost worn out CAT together. But usually when that happens it goes a while without a code between resets. Sounds like yours is pretty immediate?

I also suggest changing the plugs prior to a Cat replace - so you have time to make sure you don't get a misfire and ruin a new cat early.
 
Thanks for the replies.

Ran 2 bottles od CataClean per recommendations with a full tank of just premium gas in between.
This model year stores codes, so even if they are cleared and MIL is off, it likely have showed up in the history.. It takes a few drive cycles to have them removed from history. It comes on each morning now.


Elevation from Phoenix to where I am is about 4000 ft difference (Not sure that matters tho)

I checked just 1 plug as a quick sampling, it looked good. I will pull the rest and inspect/replace as needed.

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Do you mean to say, still comes back, with single 02 sensor replacement...

I'd be curious what happens if all are replaced (assuming 4)....
 
P0420 alone with no other codes, and no exhaust leaks before the cat, usually means you need a new cat. And of course, replace the oxygen sensors along with it.

Exhaust leaks usually make noise. Check the flex pipe between the front and rear cat.

What kind of shape is the rest of the car in? If you're not keeping it too long, just get a cheap cat on ebay. If you plan on keeping it more than a few years, get something better.

Unfortunately, there are no CARB-legal cats in stock for your XC70, though Summit can ship you one in three weeks. You can also use Rock Auto's "out of stock/notify me when available" button to get a notice, but since it's the same brand that Summit sells, it will probably become available around the same time Summit gives.

The California-legal cats have more precious metal wash coat and will last longer. California requires a 5-year/50k warranty on catalytic performance, while federal cats only have a 2-year/25k warranty. Therefore, if you plan on keeping the car awhile, it's worth getting a cat that will last awhile.


SC Maintenance said:
My guess is the original owner reset the codes prior to sale. Did you check to see if all the readiness monitors were set?
Click to expand...

I thought this too :sneaky:

Next time, look at the monitors (the scan tool will tell you). If more than one is not ready, it means the codes were recently cleared.



SC Maintenance said:
Either way - what does your long term fuel trim look like? Should be +/- 5% hopefully.

MAF should be about same number of grams / s as displacement - so in your case around 3.0 grams/s at idle.

If everything looks good I would run a bottle of kataclean through it. It won't "fix" it, but if the code goes away for a while its likely the CAT. Could also be a lazy rear 02 sensor. Could be a combination of things - old plugs, lazy 02 sensor, almost worn out CAT together. But usually when that happens it goes a while without a code between resets. Sounds like yours is pretty immediate?

I also suggest changing the plugs prior to a Cat replace - so you have time to make sure you don't get a misfire and ruin a new cat early.
Click to expand...
 
What kind of shape is the rest of the car in? If you're not keeping it too long, just get a cheap cat on ebay. If you plan on keeping it more than a few years, get something better
Click to expand...

Car is in great shape cosmeticly. This was kinda my commoner's bucket list car. Sold my Suburban and used the proceeds to get this. Quick and nimble, holds what I need it to, better MPG.
So, likely a new CARB Cat.

Didn't find ant leaks with the shop vac blowing method. Couldn't see or get access to the exhaust manifold, though I don't hear any exhaust leaks.

$800 windshield replacement scheduled for tomorrow, new tires in the coming weeks, just did $600 in maintenance. Brakes, 2 trans spill'n'fills, & few other minor things .

So maybe after Christmas I'll look at replacing the CAT. 1 last ditch effort is downstream O2, but it appears to be reading rich/lean - Downhill coasting it goes to 0, and lead foot makes it go high. Albeit fluctuates at idle.
 
Is it burning oil? Don't write this off as I had a Trailblazer that ended up being a oil issue. 2 mechanics swore it was the cats but 700 miles after a new cat was installed the code came back. Ran hm oil for a year, consumption ceased and codes never came back. Another possibility
 
I think it is burning some, although I have been doing short OCIs to clean a bit. But only 2 OCIs so far, so I dont know how much it burns. Used LM flush after the last short OCI. Running VRP now. Also put in Hy-per lube ZRP that I had in my stash (now discontinued) it was an ester based, no-zinc alternative (I believe)
 
Cmobile said:
I think it is burning some, although I have been doing short OCIs to clean a bit. But only 2 OCIs so far, so I dont know how much it burns. Used LM flush after the last short OCI. Running VRP now. Also put in Hy-per lube ZRP that I had in my stash (now discontinued) it was an ester based, no-zinc alternative (I believe)
Click to expand...
If burning, I would give it a year and see before throwing good money at a cat and it's not the issue
 
Cmobile said:
I think it is burning some, although I have been doing short OCIs to clean a bit. But only 2 OCIs so far, so I dont know how much it burns. Used LM flush after the last short OCI. Running VRP now. Also put in Hy-per lube ZRP that I had in my stash (now discontinued) it was an ester based, no-zinc alternative (I believe)
Click to expand...

Figure out how much oil it's burning, how long it takes between filling the oil and it getting low :cautious:
 
MAF fluctuates between 3.0 and 4.0 at hot idle.

Readiness codes. EVAP only shows ready when MIL off for more than a day. MiL for P040 I think negates evap test, at least till there are no pending codes.

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Sometimes downstream shows relatively steady btwn .4 - .7. Often it bounces from .8 - .1
 
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