IPD sale XeMODeX - Experts in Volvo Electronics
MVS-Amazon link helps MVS!

Get email notification of topic replies. Log in or register (free). Amazon Link Buy anything with this and it helps MVS!

2010 XC60 T6 - Eternal P0420

Help, Advice, Owners' Discussion and DIY Tutorials for the groundbreaking new Volvo S60 2011+, V60 2015+ XC60 2010-2018.
Posts: 7
Joined: Wed May 02, 2018 7:35 pm
Year and Model: 2010 XC60
Location: Denver

2010 XC60 T6 - Eternal P0420

Post by XC60Newb »

Hi all,

I've been battling a P0420 code from the CEL light for a YEAR now. I have replaced the following things. The dealer and another certified Volvo mechanic have both worked on this car (literally everything else is perfect on this vehicle, and maintained religiously) and they have affirmed no leaks are obvious in vacuums or exhaust - although, I honestly cant think of anything else it could be at this point. The dealer was the last one that touched it, fixing the fuel pressure sensor, so leaving it back with them this week. However, given that they thought that would fix it last time, and thought the O2 sensors would fix it, AND thought the Cat would fix it... (and none of these have) I have absolutely zero confidence in them this time. Looking for ANY possible insights on this. One random note, this car was originally bought in Sweden, and shipped to the USA during a work transfer (prob doesn't matter).

Please and Thank you!

- Fuel Cap
- Fuel Pressure Sensor
- O2 Front
- O2 Rear
- Catalytic Converter
- PCV Nipple (checked and clear)
Posts: 6673
Joined: Fri Nov 12, 2010 9:25 am
Year and Model: 2004 V70R GT, et al
Location: Ponder Texas
Has thanked: 4 times
Been thanked: 276 times

Re: 2010 XC60 T6 - Eternal P0420

Post by jimmy57 »

When the front oxygen sensor(s) has been used to determine fuel mixture and fuel trim has been adjusted without going out of the allowed adjustment band and then the rear (post-catalyst) sensor is not signalling the correct voltage. When front sensor is OK then the rear sensor should be .62 to .75 V under steady normal load indicting the reactions occurring in catalyst have been successful.
Since the catalyst and the sensors have been changed those pieces can be ruled out as causes now. Other things that can lead to the catalyst efficiency being out of range is one or two cylinders with partial injector blockage or an exhaust leak that allows air to drawn in before front O2 sensor. The cylinders with injector or air leak issue will be lean. Fuel trim adjustments based on frt O2 sensor will richen the fuel delivery and the AVERAGE oxygen content will be corrected but that really means that some cylinders are rich and the affected cylinders are lean. The exhaust content is NOT correct for catalyst to work. The oxygen sensors only measure oxygen but in this scenario the rich cylinders can (will) have high hydrocarbons (unburned fuel) and virtually no oxygen remainder while the cylinders with issues will have high oxygen remainder owing to inadequate fuel introduced to burn more of the oxygen.

Does the engine run smooth, particularly idling? Does it start and run well initially when cold? Engine being coarse, not a full misfire, points more to injector problem as the exhaust air leak will not affect the mixture in cylinders to make it run rough. The scavenging affects in exhaust manifold can lead to air being drawn in through a poor gasket seal, crack, or wastegate shaft leak.
User avatar
Posts: 5204
Joined: Fri May 24, 2013 6:20 am
Year and Model: S60 2003
Location: Canada
Has thanked: 102 times
Been thanked: 321 times

Re: 2010 XC60 T6 - Eternal P0420

Post by oragex »

How many miles on it? Always good to bring it to another dealer in the area, if available.

Maybe also - if not already done, google the code and check the forums for 2010+
Posts: 7
Joined: Wed May 02, 2018 7:35 pm
Year and Model: 2010 XC60
Location: Denver

Re: 2010 XC60 T6 - Eternal P0420

Post by XC60Newb »

It has 113k miles, this issue actually started 85k! Its been almost 30k miles of diagnosing, fixing, and then the light returning a couple/few months later. I am the second owner, and purchased it with 68k miles on it (dealer inspected). Zero other issues with it. I live in Colorado, and encounter all seasons and temperature patterns - no vehicle issues or concerns across the board.

The motor runs great: very steady and soft idle, and quick as well as smooth response on acceleration and deceleration. It also starts well with no auditory issues. I am not a mechanic by any means, but I have am religious with maintenance. Most fluids, filters and replacements (plugs, wires, etc.) done myself. I have an OK sense of hearing/feeling when things are off and this is one of the smoothest motors I have owned. It leads me to think there is a small vacuum or exhaust leak, that is not whining.

I will check my ODBII for the voltage @Jimmy57 mentioned above. I have checked the forums, and cannot seem to find much help. There are tons of threads on the P0420, but almost none on this model and most people are very early on in the diagnosis process, versus have fixed ALL of the things that I have already. It's a real doozie!
User avatar
Posts: 1122
Joined: Mon Aug 18, 2014 4:31 pm
Year and Model: 98 V70 T5
Location: Florida Panhandle
Has thanked: 15 times
Been thanked: 42 times

Re: 2010 XC60 T6 - Eternal P0420

Post by FLXC90 »

My son and Daughter-In-Law have a like vehicle w/approx. 135k. When they bought it last year, it threw the 420 just before a cross-country move. Ordered a cat, and the light went out! 15 months later, as they returned to FL from WA, the light came on during the trip home, and extinguished again by itself. I like Jimmy's theory of "fouling" injectors. I don't think a vacuum or exhaust leak would be as transient, and fuel quality, combined with altitude/density and fuel formulation differences make sense. At least in our case. With your constant light, I would suspect a leak is more possible.
Current Volvos:
1998 V70 T5, 112k sat 5 years, still in mechanical coma (finally at the top of the pile )
2004 XC90 T6 AWD: 186k, 60 on transaxle ( traded in )
1998 POS70 N/A: DD/training aid, 236k but really about 240k, I think...ABS module( passed on to son who sold it)
User avatar
Posts: 5051
Joined: Mon May 25, 2015 2:30 pm
Year and Model: See Signature below.
Location: Kansas
Has thanked: 3 times
Been thanked: 645 times

Re: 2010 XC60 T6 - Eternal P0420

Post by RickHaleParker »

Possible source
  • Misfiring
    Leakage in the intake system
    Leakage in the exhaust system
    Faulty fuel pressure
    Uneven compression
    Damaged catalytic converter.
Take some Ether (starting fluid) and spray it around the intake with the engine running. If there is a intake leak you will hear the engine surge when the leak sucks in the Ether. A smoke test can also find not so obvious leaks.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD.
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
Posts: 4
Joined: Sun Nov 30, 2014 5:53 am
Year and Model: 2010 S80 T6
Location: Lockport
Been thanked: 1 time

Re: 2010 XC60 T6 - Eternal P0420

Post by slovi1 »

2010 S80 T6 (103K miles) - I am in a similar situation. I changed number of different parts in the last 7 months. I have been using a local shop and that probably has been mistake in itself as they started with most expensive parts but yet were not able to resolve an issue. I gave up on the shop since and may try a different shop as my mechanical skills are on the light side (they are only as good as you tube videos and detail write ups around here).

Changed the following in this order:

Cat (shop)
O2 sensors front and back (shop)
smoke test (shop) - no leaks supposedly
Spark plugs (myself)
Air filter (myself)
PCV Oil Trap (myself)

But the dreaded P0420 keeps coming back. The engine runs smooth, millage is decent, I don't see any issues with acceleration or idle. One thing I noticed (but that could be a coincidence), that 6 out of 7 times the CEL came up, was during highway driving. Not sure if that would give me any clues as to what the underlying issue might be. I have been reading various post here and based on my reading it sounds like the next thing I may need to try is:

Fuel Pressure Sensor replacement
Techron my fuel injectors

Not sure what's left after this. I guess hidden/minor leaks? I just don't get it why these cars have so many emissions issues. I see all those old, beat up cars on the roads and most of them probably never seen what the engine light on looks like. I consider this car pretty low millage but it just chokes on the emission setup.

The only bright side to this so far is that most of the part I have already replaced (outside of maybe catalytic converter) would need to be replaced anyways if I want to keep this car for another 100K+ miles. So it is not all wasted effort/cost. I really like this car but it is a major pain and every time that CEL comes back up after another part was replaced, it just ruins my day.
Posts: 1
Joined: Tue Sep 24, 2019 6:14 am
Year and Model: 2011 XC60 R-Design
Location: CA
Has thanked: 1 time

Re: 2010 XC60 T6 - Eternal P0420

Post by Turand12345 »

My CEL just came on and I had it scanned, P0420 is the code...98k miles, engine runs strong, and smooth as butter.

I am the second owner, just got the car about a month ago, just had transmission fluid flushed ($426) and 5k service done ($53--I did notice that a few weeks after the oil change (when the CEL came on), the oil level was WAY low, so I took the car back and had them top it off).

The mechanic that did the pre-purchase inspection ($150) noted that "in the past" three cylinders had "DTC's ECM-PO30400 (500 & 600) Misfires Detected"...it was uncertain as to when these "misfires" occured. Mechanic said it was possibly a coil issue and $550 to replace them all. But, as it currently stands, all of them are working, so no immediate need to replace any of them.

Jimmy57 (above) did seem to touch breifly on, "Engine being coarse, not a full misfire (I am wondering what this is...?), points more to injector problem as the exhaust air leak will not affect the mixture in cylinders to make it run rough." Does anyone think that replacing the coils would resolve the P0420 code (even though the engine isn't currently misfiring--not that which is noticable)? I would much rather fix the source of the issue than fix whatever is down the line.

I now see why the previous owner sold the vehicle.

Posts: 1
Joined: Tue Oct 15, 2019 7:38 am
Year and Model: 2010 XC70
Location: Ontario

Re: 2010 XC60 T6 - Eternal P0420

Post by mishafrolov »


Having the same issue with my 2010 xc70 T6. P0420 is on when after 10 min on the highway.

So far:
- Replaced O2 in bank two with OEM unit
- OEM plugs
- Cyl 6 coil pack as it was showing a misfire
- PCV was cleaned/replaced by the dealer

I have a hard time believing that the cats are actually bad on a vehicle with 88k miles on it.

Any additional help/pointers would be appreciated.
Posts: 7
Joined: Wed May 02, 2018 7:35 pm
Year and Model: 2010 XC60
Location: Denver

Re: 2010 XC60 T6 - Eternal P0420

Post by XC60Newb »

Hi Everyone,

Just an update here - I am the guy that posted the original thread. I am still having the same problem (full list of replacements below). I have honestly given up, it just doesn't bother me anymore - maybe when I go to sell it I'll care again. I am taking my car in for a trans. flush later this year, and I will have them diagnosis the issue once again - this time testing the engine (compression, injectors, firing timing, etc.) as that is literally the only thing I can imagine it being. UNLESS there is a TINY leak in the intake tube that I just can't find or see. That tube is made of plastic+rubber and goes pretty far back behind the motor, so anything it's possible.

I'll keep everyone posted.

- Fuel Cap
- Fuel Pressure Sensor
- Fuel Pump
- O2 Front
- O2 Rear
- Catalytic Converter
- PCV Nipple (checked and clear)
- MAF checked, cleaned, and clear
Post Reply
  • Similar Topics
    Last post