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Discussion Starter · #1 ·
My engine light is on and my scanner is telling me that it is P0420: Catalyst System Efficiency Below Threshold. Now i looked at the voltage of the O2 sensors and bank 1 sensor 1 is completely blank while bank 1 sensor 2 is giving me readings jumping from .3 to .9. Now i also had a mechanic friend look at it for me and he was saying he got the same readings and that he was getting a low fuel pressure code along with the P0420. I'm wondering if anyone has dealt with this and if you have what you had to replace to fix. I don't want to just start replacing things and not fix the issue. My mechanic friend told me that it could be a bad injector but he was originally leaning towards catalytic converter. I've searched the forums and cant seem to find anyone with a similar issue. Please help!
 

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My engine light is on and my scanner is telling me that it is P0420: Catalyst System Efficiency Below Threshold. Now i looked at the voltage of the O2 sensors and bank 1 sensor 1 is completely blank while bank 1 sensor 2 is giving me readings jumping from .3 to .9. Now i also had a mechanic friend look at it for me and he was saying he got the same readings and that he was getting a low fuel pressure code along with the P0420. I'm wondering if anyone has dealt with this and if you have what you had to replace to fix. I don't want to just start replacing things and not fix the issue. My mechanic friend told me that it could be a bad injector but he was originally leaning towards catalytic converter. I've searched the forums and cant seem to find anyone with a similar issue. Please help!
Most likely an O2 sensor died.

The system measures catalyst efficiency by comparing the readings from the O2 sensor before the catalyst with the readings from the O2 sensor after the catalyst. If one of those sensors dies the ECU can't compare the readings properly and it will throw that code.

It's possible that it's the catalyst, but my experience is that it's usually an O2 sensor. In your case, likely the one reading 0 volts.
 

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the upstream O2 ( before the converter)sensor should be showing variable voltages as the car is running. This shows it is sending it's signal to the ecm to maintain the proper air/fuel ratio. The down stream sensor ( after the converter) will show a fairly stable voltage variance , indicating that the converter is doing it job and the fuel mixture is correct.
As stated before, it appears either your front sensor is bad or not receiving power. I'd fix that first.
 

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How many miles on the car? If it’s up past 80k the 02 sensors can be considered a wear item and are far more likely to be the cause of your codes than actual cat problems.
 

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Discussion Starter · #6 ·
Just turned 82k so I will definitely get the upstream one ordered and the downstream if it doesn't go away. Thank you for the help!
 

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so, to save you a little money. After clearing your code, see what the two sensors are now saying. The front should be bouncing around with voltages and the rear should be relatively steady. If it is, and the code doesn't return, you could get by with not replacing the rear sensor. The other argument is that you still have a sensor with 82,000 miles on it....your choice.....
The normal sign of a converter having issues, such as becoming restrictive, is the rear sensor readings bouncing up and down.
You could replace the sensor and hope that's it. I probably would, with fingers crossed.....
If your converter is an issue, don't forget to check the warranty rights concerning exhaust emissions and failures. The converter might be covered.
 

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Discussion Starter · #8 ·
What sensors do you guys recommend? I was told these cars are sensitive to different sensors? I don't want to drop 300 a sensor so is there an aftermarket one that works?
 

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I haven't replaced mine in the volvo yet. In decades of doing my own work, i've been told that the manufacturers' sensors are made specifically for that computer. So, depending on ease of installation, I decide whether to take a chance on aftermarket or not. At least if you go aftermarket, get a reputable name brand, ......bosch...
 

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What sensors do you guys recommend? I was told these cars are sensitive to different sensors? I don't want to drop 300 a sensor so is there an aftermarket one that works?
Bosch very likely makes the OEM "Volvo" sensor.
 

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I don’t think I’ve heard of a single instance of a cat actually going bad on one of these so it’s highly likely it’s the failing 02 sensor(s) at this point. Keep in mind that you can ruin your downpipe if the 02 sensor falls apart on its way out. My upstream 02 sensor left its threads behind in the dp when we tried to swap it over to a Ferrita If you’re going through the hassle of dealing with 02 sensors perhaps this could be an excuse to install an aftermarket dp to sweeten the deal a bit.
 

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Make sure the sensor you get is an exact match with wires and the connector as your original. As an example, rock auto shows sensors from $21 to $120. Some say exact fit, some don't.... Denso, bosch, ac delco are the safer bets, but even they can have multiple choices.
 

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Discussion Starter · #13 ·
So a mechanic cleared the code and I've driven a few hundred miles and it hasn't come back. The scanner readings are also correct now. That would just be a sensor starting to fail right?
 

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I have ordered a cheapie on eBay as my CEL came on after installation of the new downpipe. The V60 was actually going in for a Polestar software install when the light came on, but the dealership told me that I needed to install a oxygen emulator.

Many forums say a simple extension/spacer is all that's needed, and one guy said a 50mm spacer is needed.

Hopefully that's an easy solution
 

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My engine light is on and my scanner is telling me that it is P0420: Catalyst System Efficiency Below Threshold. Now i looked at the voltage of the O2 sensors and bank 1 sensor 1 is completely blank while bank 1 sensor 2 is giving me readings jumping from .3 to .9. Now i also had a mechanic friend look at it for me and he was saying he got the same readings and that he was getting a low fuel pressure code along with the P0420. I'm wondering if anyone has dealt with this and if you have what you had to replace to fix. I don't want to just start replacing things and not fix the issue. My mechanic friend told me that it could be a bad injector but he was originally leaning towards catalytic converter. I've searched the forums and cant seem to find anyone with a similar issue. Please help!
Sounds like an upstream O2 sensor to me.
 
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