2010 XC60 T6 - Eternal P0420

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Joined: Mon Mar 23, 2020 9:58 pm
Year and Model: 2010 XC60
Location: ON

Re: 2010 XC60 T6 - Eternal P0420

Post by jhock »

I too would not expect a code to pop up for the thermostat. My 2010 T6 was not warming up sufficiently in the winter (air in the cabin would never quite get warm) so I got an OBDII reader and sure enough the temp never got over 80C even in stop and go downtown traffic for 45 minutes. Changed my thermostat and saw exactly what pgill posted, failed in exactly the same way. But it had been that way for at least weeks, maybe longer because I might not have noticed during the warmer weather. Strange to me as heavily as the car monitors itself that it never warned me about the broken thermostat.

I also have the P0420 code pop up about twice a year (usually in the shoulder months and almost always in the Fall), but it always clears itself in about a month or so. When I look at the readings in the test, it is only barely outside the maximum parameters to set the warning. Eventually it takes care of itself, but I am not sure how or why.

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Post by pgill »

J Hock,

That is excellent information.

Thanks for confirming that the Thermostat had failed and that no check engine light was set.

Now if you can please let the MVS collective know if P0420 returns this winter or if the Thermostat made the difference.

I do have the following observation to share with the group

To evaluate the Catalytic converter the ECU at idle will temporarily create a lean mixture and then switch to a rich mixture and it monitors how long before the change is detected by the Oxygen sensor after the Cat.

According to Denso "Lower Cylinder pressures and leaner mixtures require longer ignition time to combust"

Also according to Denso a cold engine needs a richer mixture.

These two factors combined can lead to quenching and the Iridium TT's are advertised as resistant to quenching.

This is the reason why I am switching to the Iridium TT's in my 3.2.

In this context Quenching can be thought of as partial burning. If the air fuel mixture extinguishes when the ECU is trying to check the catalytic converter efficiency then the measurement isn't going to be meaningful and I suspect that is why you get a P0420. As I stated above I fixed my neighbors P0420 (Toyota not Volvo) and the only change was the Iridium TT Sparkplugs.

One last thought the 3.0T is lower compression than the 3.2 which should make it more susceptible to Quenching due to lower cylinder pressure.

Just my $.02



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Year and Model: 2010 XC60
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Post by XC60Newb »

I added the spacer, ran some Techron (two tanks @ recommended Oz/G) and replaced the PCV box because.. well why not at this point. Once I reset the code and the ECU, I went over 1,500 miles without the MIL. I have yet to go more than two tanks without the MIL in literally 4 years. However, after about 1,500 miles (was on a road trip), it came back on. To my surprise, it was NOT the P0420.. it was a P2096 (Post Catalyst Mixture Too Lean). I have now gone almost 3,000 miles without a P0420, so that seems fixed.. but at the expense of another, similar code. My hunch is that this is the same Oxygen sensor, now being far-enough removed from the pipe to read 'too much air'. There are no symptoms.

The vehicle has been and still does runs great. No hard starts, stumbling, misfire, loss of power, etc. It is smooth. Still, I will check all of the vacuum lines, and MAF, and exhaust.. again.. to see if I can get this code to go away. At this point, I honestly don't think there is anything to fix it besides replacing the entire intake, fuel and exhaust system piece by piece, and I will not do that. Every dealer and private Volvo technician that I have been to (2 of each) is stumped. They all say just deal with it, it's just new sensitive sensors and cats and not worth the $$.

I kinda feel like selling it now. Volvo wont stand behind this vehicle or issue any longer, so makes me not want to own another one. The last thing I will say, and which I have told Volvo, these cars are way too smart and the codes are way to common to lack this much specificity. They need to separate the fuel, ignition and exhaust codes out into the various sections of the system, more specificity to identify these codes.

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