On my 2001 E320 AWD wagon [94K] I'm getting these 2 codes only:

P0422 - Main Catalyst Efficiency Below Threshold (Bank 1)
P0432 Main Catalyst Efficiency Below Threshold (Bank 2)

I've cleared the codes often and within 15 restarts they reappear again with the CEL staying on till I clear it again.

Work recently done:
new battery
new Bosch spark plugs +2
New air filter
Cleaning of the MAF with CNC cleaner
High test gas only

Wagon runs strong with no hesitation at all but the CEL reappears with the same messages:
P0422
P0432

Help with any suggestions at this time![/align]

 

Hi,
The Cat (as measured by the O2 sensors) readings do not align as they should. i.e. after the cat is worse than before or alternatively the improvement is only very slight.
This could be because the fueling is out, the O2 sensors are not working correctly or the cat is scrap (not working correctly due to contamination).
First thing to check out is the O2 sensors.
Are they cycling correctly and what are the readings including max and min cycle readiings.
Its strange that both Banks are reporting the same problem which suggests a common problem.
Unusual that both cats go down at the same time unless you got some bad fuel or other contamination (silicon for instance).
Likewise that both O2 sensors go bad unless of course they have gone down due to bad fuel / contamination.
The only common cause is the MAF/fuelling but I would have expected different codes.

O2 sensor readings is the first step.

What is the mileage and vehicle history?

Stuart.

 

Stuart,

The mercedes has 94K and I'm the second owner---after all that I've recently have done the car runs very strong with no hesitation at all--the cats make no noise so I'm lost at this time the course of action--have put many tankfuls of high test in and the same results--15/20 restarts and the CEL comes up--how to test the O2 sensors--LMK any other thoughts you may have--thanks for all your help!

 

Rattling cats is a totally different issue to a poisened cat or O2 sensor.

Once poisoned the cats can't be revived by using good fuel.

Next action is to get diagnostics hooked up and look at the O2 sensor output. This will show whether O2 sensor is bad without paying for new O2 sensor should they be working OK. I suspect you will find thay are working OK because you state the car is running fine.

If the O2 sensor is working OK then it looks as though the catS have gone bad. If so then I suspect bad fuel for both to have gone simultaneously.

Have you had misfire problems in the past which have now been corrected? This is another cause for cats going bad.

If the engine pulls strongly, starts and runs fine and has "normal" gas mileage it seems to confirm that the fuelling is OK and that the cat is not working correctly.

Expensive!! So make sure the other possibilities have been correctly closed off first.

Just concerned that the cats could go without the O2 sensors also being damaged. Maybe the O2 sensors have been changed since the poisioning/misfire event which could have been some time ago.?

Stuart.