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B5254T2 Engine (2.5T) Catalytic Converters All Going?

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dono
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B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by dono » Sat Sep 21, 2019 8:56 pm

I have been looking for/inspecting XC70's 2004-2006 over the past month from craigslist looking for my Goldilocks used volvo and I have noticed a pattern - a majority of the cars I inspect have some form of Catalytic Converter efficiency code. The CEL's are not illuminated and I can only pick up the Cat codes with enhanced scanner function specific to that make year and model - it doesnt show up on the generic OBDII codes.

Some of the vehicles have been well maintained some not so much. All have been in the 140,000 mile range. The owners often report having had O2 sensors changed within the year as a solution that has eliminated the CEL (so they say) but I can see on the live data that the voltage at the second O2 sensor is out of spec going from .080v - 700v most often at low idle after revving. I should note my own 04 V70 2.5T AWD w 242k has the same symptoms but it is throwing CEL and I know there are many culprits existing as underlying causes of Cat issues.

I know bad Cats are made not born so I have rejected these cars thinking they have a bad Cat AND other underlying issues. So my question is - are all of these 15 year old cars at the end of their Cat life spans or are the engines basically now burning enough oil that they are destroying the Cats?


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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by RickHaleParker » Sat Sep 21, 2019 11:56 pm

Clogged Catalytic Converters are rare, even for a 25 year old car. Test drive the car. If you can get it up to highway speed without hesitation or reluctance, the Cat is not clogged.


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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by Rattnalle » Sun Sep 22, 2019 4:09 am

Cats aren't supposed to fail ever. Poor quality fuel or other issues can change that of course. Over here it's extremely rare for some reason.



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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by abscate » Sun Sep 22, 2019 6:00 am

That cat efficiency code is rarely the cat, it's usually some other fuel issue. Changing the OXS will clear the code but not solve the issue. By the way, the PM model replaces OXS after100kmiles and certainly by 150k miles.
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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by Rattnalle » Sun Sep 22, 2019 8:37 am

The sensors shouldn't ever need replacing either if everything else is fine. Must be something in the air over on your end if it's common.

My car is at 200k mi and and pretty sure everything is original down there.



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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by dono » Sun Sep 22, 2019 9:02 am

RickHaleParker wrote:
Sat Sep 21, 2019 11:56 pm
Clogged Catalytic Converters are rare, even for a 25 year old car. Test drive the car. If you can get it up to highway speed without hesitation or reluctance, the Cat is not clogged.
The most common causes for Cat failure are 1. Unburned Fuel 2. Coolant Leak and 3. Oil Consumption. It is true that unburned fuel can destroy the cat honeycomb structure and lead to blockage. Coolant leak and oil consumption can destroy the cat without causing blockage.


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Re: B5254T2 Engine (2.5T) Catalytic Converters All Going?

Post by oragex » Sun Sep 22, 2019 2:31 pm

The cat on these car is of very high quality (and really expensive to replace, aftermarket are a hit or miss and may not pass some inspections). Aftermaket O2 sensors can also throw a cell

Indeed when an ignition coil fails (engine starts missing and shaking a little), we need to stop driving or at least disconnect the injector on that cylinder.

Turbo engines also can suck oil from the turbo I guess, another potential problem for the cat

But my first hint goes to a leaking flexible downpipe (after the exhaust manifold). Very common as these cars get older, you can even see the outside mesh is rotten. The leak develops where the flex pipe enters the manifold, and may not be noisy or smell. It may however foul the secondary O2 sensor reading from what I've heard. Replacing the flex pipe is all but fun (cut & weld) and the flange after the cat also starts leaking and needs be fixed
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