judeshi

Hello Everyone:
I have a 2012 S550 Base (W221) with 67000 miles and it has check engine light on. I went to a mechanic and had it checked by SnapOn scanning software and it has error code P430 which leads to bad CATS. I wonder if the car is burning oil since I have to add about a quart every 3 months or so. Is that abnormal or normal for a quart to burn around 3 months or so? Is the burned oil going in the CATS via the exhaust system? Or could the O2 sensors be bad. Following is what I have tried so far to fix this issue.
I purchased (2) different CAT cleaners, first one CATAclean and second Dura Lube and added to the gas tank (not at the same time and followed directions on the bottle) and check engine light went away. Two week later the light came back on.

I am wondering if I have an internal oil leak which causing burnt oil to go in exhaust and messing up the CATS or O2 sensors are bad and not making proper exhaust reading or totally something else.
Any help will be huge for me in this forum.
Thanks,
Jay

kbob999

There could be a lot of possible causes to the bad Cat issue, and they all sound expensive.
bad injectors
bad cats
bad spark plugs or coils causing misfires (would likely give more codes)
leaded fuel
burning oil
bad O2 sensors
etc.

Do some searching and reading of others who had this issue, and what the repair was for them. I'm not sure there is one silver bullet, but a lot of paths to follow.

FYI - my car burns no oil, and does not leak any oil, so that could be a clue to your issue.
I don't know if you have external leaks, and I can't think of any internal leak sources other than PCV systems.
Remove the oil cap and see if you have a lot of blowby coming out. Stick a rubber glover over it and see if it billows up. If it does blow up quickly, you have bad rings, and that is where the oil is going.

Good luck and keep us posted on the outcome.

judeshi

Your points are all valid and I will try you rubber glove test and see if it blows up. Independent Benz Mechanic told me about leaded fuel as well that you mentioned, we always fill it up with supreme at Speedway or Kroger near my home, but he said in S550 always use Chevron or Texaco. Service advisor at local Mercedes dealer said it will most likely not be cats, O2 sensors are high probability. Might start with figuring which sensor it could be and go from there. I do not have oil leaks outside the car and no drips on my driveway. Car is totally dry from any leaks underneath. It will take me some time to resolve this puzzle, but will keep you guys posted and if you think of something else, please let me know.

BOTUS

mine burns no oil for 18 months, then use 1/2 litre before I do the 2 year oil change using merc oil to 229.51 spec

if the sensor checks out as working, you could try to do an oil and filter change, stick the gunge in the tank and do an Italian tune up

to give more perspective on that code

P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
P0430 Catalyst System Efficiency Below Threshold (Bank 2)
P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)
P0432 Main Catalyst Efficiency Below Threshold (Bank 2)
P0433 Heated Catalyst Efficiency Below Threshold (Bank 2)
P0434 Heated Catalyst Temperature Below Threshold (Bank 2)
P0440 Evaporative Emission Control System Malfunction

judeshi

I am getting following error:

P0430 Catalyst System Efficiency Below Threshold (Bank 2). Mechanics are telling me that it is rare that CATS are bad, but than what is the issue. Are both O2 sensors on bank 2 bad (upstream and downstream?

BOTUS

on older Merc's blocked / collapsed CATs are common. Not heard if it on a 221.. but then in UK u can't get the wrong petrol others seem to suggest u can in USA?

oil use on modern cars is unusual, but not unknown.... how much is a qrt and in wot miles rather than time....

1ltr in 1000 miles is now high 40 years ago that was AKA as none
a engine in tip top condition used appropriately using the right oils fluids and fuel, can do < 1/2 Ltr in 10,000 miles

appropriate use means allowing it to fully warm up and using its full potential often.... driving like a girl is NOT good for engines…. Rings need the work out, both to move nicely in the lands and to bed into the cyl to get a good seal

cetialpha5

As others mentioned there could be many causes. Typical federal emissions is 8/80k but you might be beyond 8 years at this point, depends on the in service date of the car. Cats would be covered under 8/80k. What that P0430 basically mean is that you're getting the same sensor reading from both oxygen sensors which mean that the catalytic converter is shot, it's not doing anything. It's usually the upstream sensor that goes bad or the wiring, the downstream sensor measures what happens to the exhaust after going through the converter. When it's the same, nothing happened. You could try just replacing the upstream one, basically that gets cooked by the raw exhaust and the downstream one rarely goes because it's looking at the clean exhaust. You need to figure out what caused it from bad plugs to a vacuum leak or you'll just cook the next set of cats again.

Chazz Michaels

Two things I’d recommend here, get a compression test, it will ease your worries that you are burning oil due to valves or rings. The second you should check/replace your oil separator/PCV Valve. It’s a cheap fix, but it allows the crankcase to adequately breath. Its a cheap plastic piece, but if the separator/pcv is wore out, it will begin sucking an oil mist in through your throttle body and burning it in the combustion chamber. This will not only lead to blocked up cats, but will also begin oil soaking your intake runner flapper valves.

This is a cheap fix, easy to get to and a regular maintenance item....however it’s very often neglected and missed by most Mercedes owners. These would be the two most probable ways that you’d be going through oil that fast.

Hope some of this info helps, keep us updated when you get it figured out.