P0420 - Predictably triggered by gas refill

volvostud · Post by **volvostud** » 18 Jan 2023, 08:24

This happened for about a year before Covid when I ultimately parked my XC70 for 18 months. I got it running again in December and predictably it started happening again (thankfully right after I got it inspected).

Engine throws a P0420. I clear the code and it stays off for the rest of that tank of gas. Refill gas and within 20-40 miles it comes back on. It can almost always be cleared and will almost always stay off till after the next refill.

On my OBDII I read 1ish on the front sensor and a bouncing 0.05-0.85 on the rear sensor. Flutters all over the place reving or idle. I was going to just throw a spacer on it, but if I wanted to investigate further - Any thoughts? Not in the plans - a new cat.

Post by **pgill** » 19 Jan 2023, 15:20

The Catalyst efficiency test may not run if you reset the MIL light until you fill the tank.

I wouldn't do anything based on that piece of data.

If you want an analogy..........why do you keep finding things in the last place you look for them......................

Having said that I would do something about the P0420

First what is a P0420 -------- catalyst doesn't store enough oxygen

But the better question is How is it measured?
Answer: the mixture is switched from Lean to Rich to Lean to Rich and the time needed to see the switch is checked by the second O2 sensor. The Converter should store some Oxygen so that the change is seen by the first O2 sensor sooner then the second O2 sensor.

With that in mind the ECU is expecting that it can adjust the mixture between Lean and Rich without creating Misfires and that it can consistently combust a rich or lean mixture.

When everything is new this isn't a problem.

Here is what I would do to maximize my chances of igniting/completely combusting a lean or rich mixture.

1. Upgrade to Denso Iridium TT sparkplugs (Volvo did this for later 3.2's so you can just buy the Volvo part if you prefer)

2. Get a code reader that will read the Mode $06 data and check the misfire counts (replace coils if you have misfires)

3. change the PCV if #1 doesn't work

4. change the fuel pressure sending unit

5. change the Thermostat with a VOLVO or LAND ROVER original part (a know failure point) and igniting and/or completely combusting is difficult if the Engine Temp isn't controlled

6. Replace the intake manifold gaskets

7. clean the MAF (possibly replace)

Good luck

Paul

PS here is a document from Volvo that explains a bit about how the emission controls work

MY07B6324S-S80XC90AWD (1).pdf: (603.47 KiB) Downloaded 160 times

Post by **MoVolvos** » 20 Jan 2023, 08:32

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Try the inexpensive things first. I believe Robert said the Lacquer Thinner worked as with several members. Start with oil change with 5W40, Premium fuel and two bottles of Techron. The Lacquer Thinner is next if the P0420 doesn't go away. Do it in stages so you know whether it's the CAT or something else. A worn or bad CAT won't be fix by bring it back to Stage O.

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volvostud · Post by **volvostud** » 30 Jan 2023, 07:59

So between the last clearing of codes and the last tank of gas, I did replace the PCV membrane, was totally ripped. I replaced the little alternator coupling last fall and had the intake off to do it. New intake gaskets then. MAF and Throttle body were really clean, particularly for 108k. I did notice that my hose clamp just past my air filter was loose, so likely sucking some air past the MAF. BUT that could only have been loose since my last air filter change, and the 0420 has been going on for years.

But I am now 100 miles post fuel up and no CEL, so will keep an eye on it. I did at one time have it throw a fuel pressure sending code, so may as well swap that. I'll also read misfire counts, pretty sure my reader does. I'll order some plugs, due for it anyway.

Lastly, about to tackle the entire accessory side of the engine. Not expecting that has any thing to do with the CEL, but the brake pressure booster leaks, the belt is in bad shape, and at 108k it likely needs a new water pump anyway.

Post by **pgill** » 30 Jan 2023, 09:22

Excellent result!!!!!

Let us know if the p0420 comes back

As for the sparkplugs I recommend

Denso 4704 IKH20TT Iridium TT (TWIN TIP) https://www.freel2.com/forum/topic35121 ... iridium+tt

If you want a VOLVO box then these are the same part Genuine Volvo 31286359

Changing the Fuel Pressure sending unit is a good idea as well

My S80 set a code for the sending unit and then it was fine for a while but it came back viewtopic.php?t=87687&start=110

For the last item (Aux belt etc.)
Here is what I do https://www.freel2.com/forum/topic32103.html

Note: I don't change the water pump but I do change the coolant every 5 years and I change the O-ring for the power steering pump if I remove the high pressure line.

LR009387 O-ring for Power steering pump (I don't know the Volvo part number)

Here is a great video of what needs to be done

Good luck

Paul

volvostud · Post by **volvostud** » 30 Jan 2023, 14:26

On the PS pump, my wife rarely drives this car (she has a 2020 xc90) but she always tells me the steering is stiff on this car. I think it is perfect and I've only ever owned one bottle of PS Fluid, so i don't think it is leaking or otherwise going through fluid. Is there anything I should check or replace/reseal when i do the accessory belt service?

Post by **pgill** » 30 Jan 2023, 17:30

Make sure to use the Pentosin CHF202 or 11S fluid

The reservoir has a filter screen in the bottom and you should get a new Reservoir

When I changed mine my wife noticed the difference and she normally doesn’t notice anything about the LR2

Post by **pgill** » 31 Jan 2023, 08:43

Take a look at this link for a video about the Reservoir (its for the LR2 but the power steering hardware is shared with Volvo)

https://www.freel2.com/forum/topic25808.html

This is item #6 on the list

High Mileage Maintenance items for 3.2

6. Power steering fluid and reservoir replaced due to noisy heavy steering

Here is the complete list

https://www.freel2.com/forum/topic32504.html

Good luck

Paul

volvostud · Post by **volvostud** » 16 Feb 2023, 08:36

P0420 came back on the second gas refill, at exactly 40 miles post fueling. Cleared it and moving on.

Post by **pgill** » 16 Feb 2023, 10:14

Did you replace the Sparkplugs?

Let us know the timeline for filling fuel and replacing the sparkplugs.

Assuming that you have replaced the sparkplugs then can you take some pictures of the ones that you removed. My S80 (actually my niece bought it from me) had a misfire so I replaced the sparkplugs and the coil pack (because I had both on the shelf).

Note: one of the sparkplugs was oil fouled and I installed Denso Iridium TT but just in case I also ordered a Denso Iridium TT plug that is hotter than stock. (a hotter plug will burn off the oil deposits) If you need to go down this route I can let you know what I bought.

Note: the sparkplug that oil fouled was replaced by me in DEC-2018 it was an Denso Iridium Power. So it did last a while but when it failed it failed hard. My S80 unfortunately have the "Improved Oil Rings" and it does consume oil.

The whole story is here viewtopic.php?t=87687

go to page 21 to see the oil fouled sparkplug

Good Luck

Paul