⭐⭐⭐ Thread of how to find the values of your primary catalytic converters. (NEW)
Background
The P0420/P0430 codes, or Catalyst Efficiency Below Threshold code is merely the secondary O2 sensor sending a signal out to the DME and the readings of the exhaust are out of normal range (can be in both frequency and amplitude). This could be the exhaust gases or the O2 sensor itself. The code occurs with the secondary or downstream O2 sensors, after the primary catalytic converters (cat is integrated with the exhaust manifold).
The main reason automakers decided to put primary cats in the exhaust manifold was to get catalytics to heat up quickly to meet cold start emissions standards. These primary cats can also have more dense cell packing, thus why you may see issues with the primary cats industry wide, but not as much with the secondary cats. The newer cars with turbo engines cannot use an exhaust manifold/catalytic combined part (usually turbos are integrated into the exhaust manifold in newer engines), thus they may have both the primary and secondary cat material in one catalytic unit. You will know this because typically the secondary O2 sensor is in the middle of the catalytic, between the primary and secondary catalytic material. Back to the 3.2.
- Primary catalytic with the primary O2 sensor before the catalytic. Role of the primary O2 sensor is to adjust engine running based on combustion gases. May adjust ignition timing & fuel with lean/rich readings. The primary O2 sensor readings are constantly switching to adjust for factors such as engine load and rpm.
- Secondary catalytic with the secondary O2 sensor between the primary and secondary catalytics. The flex pipe is also the downpipe and the secondary catalytics do not get read. The role of the secondary O2 sensors (#5, #6) is to montior gases after the primary catalytics only, if the primary catalytic converter is doing, or can do, its job. The readings of the secondary O2 sensors are usually more constant.
⛔ If you want to see how not to approach P0420/P0430 and oil consumption in the 3.2 engine, you can read this long thread. The key to improving oil consumption and catalyst efficiency codes is to use good parts that are known/verified to work and to verify in diagnosis instead of making assumptions.
⭐ There are two main reasons for the P0420/P0430 codes, both usually a lack of maintenance:
1) Engine & exhaust maintenance
2) Engine oil changes
1) Engine & exhaust maintenance
Exhaust
First step in assessing the code is to do a visual inspection of the exhaust because rust is normal for the flex pipes/downpipes. Holes allowing atmospheric air into the exhaust before the secondary 02 sensors will throw off the readings.
RyanR’s thread about changing his downpipes/secondary catalytics which caused a P0420 code
Engine
It goes without saying that the catalytic specification is for a normal running engine. When an engine is not maintained, the catalytic, especially an older one, cannot convert these gases to within the normal emissions range. This results in the secondary O2 sensor readings outside of normal range. Of course, you should read the stickied 3.2L (B6324S) Engine thread and read it again and again. Volvo recommends changing several engine parts at 150k miles, but I recommend closer to 100k miles since parts like the PCV have been seen to go as early as 100k-130k miles.
(TIP) Trust the maintenance process outlined in the 3.2 engine thread linked above. You can get caught up on the maintenance if you have delayed maintenance and high miles.
Some of the main issues are:
- PCV – change the entire unit with a good quality one. I recommend using a branded Volvo or Land Rover. A bad part may lead to some oil consumption as the job of the PCV is also known as an oil separator. This can also affect the vacuum and air/fuel. Changing to a new OE PCV could alleviate oil consumption and P0420/P0430 codes.
- Unmetered air – extra unmetered air is getting into the intake. This could be from loose intake boots, to intake seals (intake manifold), loost MAF, etc. Check all intake parts are tight and working. This might have been caused by previous work.
- Ignition – Quality spec’d parts for spark plugs and maybe ignition coils
- Air filter – no need to explain this
- Fuel – dirty fuel injectors may have a leaking injector or improper spray. Try a modern fuel system cleaner (not seafoam). Rich running or improper combustion of fuel can increase the chances of soot. Read below because synthetic oils are better at preventing (resisting?) soot.
- MAF – well, this part would throw a code. Change if there is a code.
- O2 sensors – once in a while (rarely) a primary O2 sensor will go bad prematurely and is improperly adjusting the ignition and fuel. Also, a secondary O2 sensor may go bad improperly reading the exhaust gases. The regular engine maintenance should be done first no matter what. Then the graphical readings of the O2 sensors can help determine a bad O2 sensor.
The usual can occur in all engines. that a rich running engine can push fuel into the catalytics where it combusts, damaging the catalytic internals. A lean running engine can get hot and may overheat a catalytic, damaging the precious metals.
2) Engine Oil Changes
Volvo did a disservice with their ~7k mile oil change intervals using conventional oil. Servicing a 3.2 at the dealership can lead to issues IMHO.
(Edit, added questions & answers below)
Q: Do all 3.2s consume oil?
Q: Does it matter which year 3.2?
A: No, real-world feedback from owners shows the same results and application for both variants of the 3.2 engine.
Q: Is there an engineering flaw?
A: Not really. unlike the P3 platform 2.0 (forced induction) and 2.5t engine which saw oil consumption as early as 30k miles and 60k miles, if there are poor oil changes that contribute to oil consumption, it’s not usually seen until over 100k miles. The 3.2 is a naturally aspirated engine (no turbo or forced induction).
The problem is oil consumption and the relation to piston rings. Some oil consumption could be caused by a broken PCV, but oil consumption could also be caused by the piston rings which occurs in both versions of the 3.2. The entire auto industry has used, or still uses, lower tension piston rings. The reason is to reduce engine friction, improving both emissions and economy (MPG). The issue is combine this with extended oil intervals, and this leads to oil blowby & excessive oil in the combustion chamber. The lower tension piston rings allow more than normal oil through to the combustion chamber and the extended oil intervals lead to carbon and soot build-up in the piston rings. The theory is the 3.2 has lower tension rings as a modern engine.
Oil blowby is an issue because the oil then goes on to contaminate the primary catalytic converters. While old mechanics say it’s normal for oil consumption, in newer low-emission vehicles it can lead to the P0420 codes. That oil may also ignite in the catalytic as it heats up, and the combustion damages the primary catalytic internals. Oil can also contaminate the O2 sensors.
The remedy:
- Use a good synthetic oil at a 5k mile oil change interval. I recommend Mobil 1 0W-40 (other quality 0W-40 oils work too such as Pennzoil). The reason is not to contribute or continue contributing to the issue.
- Some people have tried to use an engine flush (@John C and @EJfromupstairs) with good success in reducing oil consumption. The theory here is that it helped remove the carbon build-up in the piston rings.
- You could also try the top-end piston ring cleaning, but the engine flushes just might do a better job and it’s easier to do.
- Note: don’t get trigger happy with engine flushes. Besides that it removes carbon and puts it into the oil, it also can dry out the seals. That’s one of the reasons why it’s only recommended to use for a short time. Don’t go leaving it in the oil for days or weeks. Also, if you need to repeat the process, wait an oil change or two (edit: could be a shorter oil interval between). Search oil engine flushes with Liqui Moly engine flushes and you will find many YouTube videos on it.
- If the catalytic is plugged with oil, will an emission fuel additive help? Maybe, maybe not, maybe for a short time. After doing the engine maintenance and fixing oil consumption, just driving it normally may help clean out the cats, but who knows the amount of internal damage already done.
If the cats are too contaminated or damaged from oil consumption, then the only other fix, unfortunately, may be replacing the primary catalytics.
(We do not see valve stem seal issues with the 3.2.)
Conclusion
If you notice the theme, the best way to avoid a P0420 code is to follow proper maintenance with good parts and fluids. Even washing the undercarriage after driving through winter salted roads can help prevent rusted flex/down pipes, or at least extend the life. Don’t wait until there is a problem with your 3.2 to do proper maintenance or to tackle an oil consumption issue. There is no magic here and the 3.2 is not flawed. Volvo and the owners are the flaws if proper maintenance is not done. 