2001 2.9 Catalytic Converter Diagnosis; Codes P0422, P0432

[DanSC]

Hello,

I have a 2001 2.9 that is creating P0422 and P0432 codes (main catalyst efficiency below threshold bank 1 & 2), but is otherwise running fine. It doesn't feel low on power, I don't smell anything unusual, and whacking the catalytic converters with a wrench doesn't create a rattling sound. The car has about 175k miles.

Today I used a infrared thermometer to measure the surface temperatures before and after the converters. The ambient temperature was about 75 F. Before the two initial cats I read around 315 F. I read about 285 F after the first two cats, and about 275 after that. Below is my best Microsoft Paint diagram of where I measured. My car has the two upstream and one downstream converters.



To me, this says I should replace the catalytic converters and oxygen sensors. Is this a reasonable diagnosis?

[SuperHerman]

I would do a little more digging. Does the car use any oil? How do the spark plugs look? Any signs of oil burning? What I am looking for is something that may cause your cats to fail. Although you have 175k that does not mean your cats are bad - Volvo cats are pretty robust. If you do not have any of these issues I would try getting some live stream data on what your O2 sensors are doing. This will tell you whether the problem is in the sensors or the cats. If the data shows the O2 sensors are acting correctly then your cats are suspect. Many OBD2 readers will provide this information.

You could also try cleaning the MAF as that is easy, quick and should be done anyways. If you have no fear and jack up the car, take out the O2 sensors and with a flash light and small mirror take a look into the hole and see what the cats look like. You are looking for holes and/or clogs (although you state you hear no noise when hitting them). Look up on the net what a cat should look like and what it should not look like. At this point I would change out only all of the O2 sensors since you are planning on this anyways and see if the new sensors resolve your problem. After all this if you have no love replace your cats.

I had a 5 cylinder Volvo that I brought to the dealer for an oil change, and they scanned the car for free. They told me I needed a new cat. I put in a new aftermarket cat, dealer said just drive it as a new cat was not worth it, and the code still appeared. I replaced the O2 sensors and the issue was resolved. Not sure if it was the sensors, cat or both. After that for the 50k miles I drove the car afterwards I had no issues.

[DanSC]

Apologies for the late reply. The plugs look fine and no sign of burning oil.

I did connect a vacuum gauge. At idle, vacuum was 20-22 psi. At a steady 3000 rpm, vacuum was 10 psi. When snapping the throttle, vacuum dropped to almost zero before returning to idle pressure.

[SuperHerman]

As the plugs look good and the car is not burning oil I would continue to look at other causes of the issue before replacing the Cats. Something other than the Cats could be causing that code - the fact you have both codes at the same time is relevant.

Try and get some live stream data on how your O2 sensors are performing - this will give you more information. Looking at the fuel trims will also tell you if you have unmetered air entering into the system. You will need to borrow or buy an OBDII reader with live stream capabilities.

I bought a few WIFI OBD2 readers of Ebay for less than $20 for my iPhone and leave them in each car - I bought an App for a similar amount and it provides all sorts of data information. If you run Android you can get a Bluetooth version.

Before spending money on a new Cat I would exclude your up and down stream O2 sensors. Also look for air leaks, failing temp sensors, bad gas ...

[oragex]

I think you have to pass emissions in your area, you need to know that most aftermarket cat converters contain very little honey comb material to reduce the exhaust emissions - I have an aftermarket one and it has less than 1/3 of material inside compared to the genuine one. You will probably almost surely fail emissions. Therefore, you are almost surely stuck to buy a genuine exhaust and you will be scared at the price asked.

One quick way to check the converter is to smell the gases at the exhaust, a rotten smell may mean the cat doesn't work properly.

Going with a used unit may be the best approach. That said, such code doesn't necessarily mean the cat is bad. In order, I would inspect (listed) to the flexible down pipe, these start leaking and this can fool the readings of the secondary O2 sensor (which is used to measure the cat efficiency). Also the secondary O2 sensor can go bad or the wiring/connector may be damaged.

One of not the main reason why a catalytic converter goes bad is un-burned fuel mixture. If the engine has a fault and the fuel-air mixture is not burned properly, the fuel will end and ignite inside the honey comb which will cause the honey comb to burn it's material. It won't necessarily show as an increased temperature on the outside.

Another reason is engine burning oil.

Before a catalytic converter is replaced, the engine ignition and fuel delivery must always be inspected. Fuel pressure, injector spray pattern and operation, ignition coils, spark plus gaps, wiring, primary O2 sensors (they adjust the mixture and when they go bad too much fuel is pumped and ends on the cat converter), all this must function well, or the new cat converter will also get damaged.

Side note, on Yotube there are a few videos with people claiming to 'clean' cat converters with acetone (??) when they throw codes. They said they get no more codes once done. Will it also pass emissions ? Who knows. I'm not endorsing this myself but hey, some people want to take a risk. By no means don't put an O2 sensor in flame or any solvent.

[DanSC]

A very, very delayed but probably final update. After a while trying to definitively diagnose the problem, a new diagnostic code appeared. P0030: failed bank 1, sensor 1 O2 sensor. I replaced it last night (surprisingly difficult!) and car is running better.

[DanSC]

Final, final update. After a few drives, P0422 and P0432 have not reappeared. I will update for posterity if they do.

[jimmy57]

Front O2 sensors or injectors are a frequent cause of catalyst efficiency codes. The front sensor's signal is effectively an average of the exh gas of the cylinders measured by it. If it reports a wrong signal then the gases entering converter can be catalyzed by catalyst. If an injector is obstructed then that cylinder is lean but the lean avg signal causes ECM to change injector opening time until the avg exh gas oxygen is within range. Two rich cylinders cover the leanness (extra oxygen) of the bad injector cylinder but the gases other than oxygen are in wrong concentrations and again, the catalyst can handle the task as it should. Exhaust leaks at head or turbos can do the same.