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Green '02 E320 Wagon
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Discussion Starter #1 (Edited)
Hello, my 2002 E320 4Matic wagon turned on the check engine light with codes P0422 and P0432 for Main Catalyst Efficiency Below Threshold (Bank 1 and 2). I want to add a gallon of lacquer thinner to the gas tank, fill it up, then immediately drive non-stop until it's empty. I did this in my 2000 Volvo V70 when it had a P0420 cat code and it didn't come back. I'll be driving 350+ miles tomorrow anyway, so it's perfect timing.

What do you think about lacquer thinner to clean out the cats? Or could the codes have been thrown by another issue? I may have a slight exhaust leak (at the clamps after the cats) but I don't see how they could cause the codes.

The freeze frame data (for P0432?) is:
Fuel Sys 1 = CL
Fuel Sys 2 = CL
Calc Load = 46.27%
ECT = 181 F
STFT B1 = 0.78%
LTFT B1 = 6.25%
STFT B2 = 2.34%
LTFT B2 = 6.25%
MAP = 21.26 inHg
Eng RPM = 1900
Speed = 53 mph

I'm suspicious of the STFT B1 being so much lower than STFT B2. In the past, I've seen them be different and be the same, so I'm not sure which is right. Are O2 sensors a common point of failure? I believe mine are original.

And of course, I have to go for inspection next month. Thanks for any input that you have.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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How many miles?
 

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Green '02 E320 Wagon
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580 Posts
Discussion Starter #3
It has 159k miles. The engine has some slight random shudders at idle even after I replaced the wires and two plugs. Otherwise, it runs great. I'd look at the supposed exhaust leaks but my community workshop with the auto lift is closed from the virus.
 

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Premium Member
1998 E320 base sedan @ 160kmiles
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6,678 Posts
The STFT and LTFTs are fine. The problem is not there. You need to check the post cat O2 sensors graphs and compare them with the ones before the CATs. The post cat ones are the ones that report the fault.
 

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Could also be the MAF that's the issue.
 

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1998 E320 base sedan @ 160kmiles
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6,678 Posts
Could also be the MAF that's the issue.
The MAF sensor issues would raise different set of codes regarding fuel trims (P0170 / P0173). It is interesting that you get codes from both sides at the same time. Think about what causes cat problem reporting from both sides.
 

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Green '02 E320 Wagon
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Discussion Starter #7
Thanks. Hopefully a muffler shop can pull the O2 sensor graphs since I've been unable to find a reasonably priced scanner with that ability. Might be cheaper just to replace every O2 sensor in the car.

Think about what causes cat problem reporting from both sides.
Is it a bad MAF sending the incorrect mix into the entire system? Many people have suggested that in the past. They also say the MAF might need replacement at 120k mi and O2 sensors need replacement at 100k mi (per Bosch).
 

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1998 E320 base sedan @ 160kmiles
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6,678 Posts
$20 BAFX scanner with Bluetooth to Torque application on Android phone should be able to display graphs and voltage levels from the O2 sensor.

You do not have a mixture problem. If you did, you would have problems with the Fuel Trims. MAF issues can cause Long Term Fuel Trim values to go beyond +/- 25 % limits. Yours are 6.25 %.

The post cat sensors are reporting the problem as the cats are not working as efficient as they should be. I would start looking fro a restriction, from the muffler toward the cats.

Do you have any other faults apart from the P0422 P0432 ?
Have you checked the heater fuse for the rear O2 sensors ?
It may be one, or both of the cats have crumbled inside and the pieces caused a blockage somewhere. A competent muffler shop can confirm.
 

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Firefox,
If you have access to a temp gun, a simple way to test the cats.
 
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