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This is a follow-up to my previous questions regarding

Customer Question
replacement of the cat converters...
This is a follow-up to my previous questions regarding replacement of the cat converters on my 2007 GL450. As I stated in my last comments, I purchased a coder reader and am attempting to troubleshoot the issue myself before returning to the shop. Based on the live data readings I've seen, I suspect I might have O2 sensor issues. Can you suggest possible troubleshooting tips for o2 sensors?
Submitted: 11 months ago.Category: Mercedes
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Answered in 48 minutes by:
7/28/2017
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 6,094
Experience: 20 years Master Certified excellent fix rate and have access to factory wiring, and instructions.
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Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago
Can you tell me the code numbers again and the scanner you are using ?
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Customer reply replied 11 months ago
I'm getting codes P0420 and P4030. I'm using an Autel AL419 scanner. Despite your warning, I cleared the codes and now the O2S monitor test will not complete. Hence, my concern that I might have sensor problems.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago
Ok :) let me see what I can get you , it may be later tonight .
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Customer reply replied 11 months ago
OK, Thanks
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago

ok aaron sorry for the delay, i cannot locate the p0420 or p0430 codes in the mercedes scanner, still from what i find the converters are the issue i looked at the last info you have given me on our other chat and its still possible that the o2s are lazy and not reading correctly, thats always a possibility, im trying to find more info on these codes, the problem is that in mercedes we can have a fault code with a suffix of 01 through 04 and they all mean something different, that is the way they are getting around the standardized obd 2 laws it seems. im still looking my friend I will try and find some info as soon as i can. Lou

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Customer reply replied 11 months ago
OK, Thanks for the help!
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago

AAron I cannot get you anything better on these codes. the best i can say is it may be worth it to replace the o2 sensors and see if the codes go away, if not you will need catalytic convertors. I will open this up to see if another expert can help. Lou

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Mercedes Mechanic: mike switzer,
 replied 11 months ago
mike switzer
Category: Mercedes
Satisfied Customers: 741
Experience: lead diagnostic tech at Aamco
Verified

whenever codes p0420 or p0430 show up it means the o2 sensors and reading properly and realizing the catalytic converters and not working efficiently. i have yet to see a vehicle of any make to this day that had those codes and it was not a bad cat.

if you have an infrared thermometer you can measure the input and output temps of the cat after a long drive. the output should be significantly hotter. around 600-700 degrees i would say if it is not that hot on the output the cat is not working as it should.

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Customer reply replied 11 months ago
While not the answer I was hoping for, I do appreciate the advice.
Any idea why the o2 sensor monitoring test will not complete after erasing the codes?
Mercedes Mechanic: mike switzer,
 replied 11 months ago

because the cat is not working properly. the test will complete when it verifies everything is withing passing range. but if it senses an issue then it will not complete and will eventually re-throw the cat codes.

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Mercedes Mechanic: mike switzer,
 replied 11 months ago

i apologize for the delayed response i had to leave early for an emergency.

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Customer reply replied 11 months ago
That makes sense if the cat system test did not complete. Why would a cat problem prevent testing the o2 sensors?
Mercedes Mechanic: mike switzer,
 replied 11 months ago

the o2 sensors are what complete the cat test. so if it cant complete the cat test it it stops running all other test.

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Customer reply replied 11 months ago
The cat test completed and threw the p0420/30 codes. All other test completed except the o2 sensor test. At this point, i see no other option other than replacing cats and o2 sensors.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 11 months ago

Aaron i would start with the 02 sensors first. those are the lesser expensive of the two, see if that helps.

lou

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Mercedes Mechanic: mike switzer,
 replied 11 months ago

if you have no further questions at this time i would appreciate if you took a moment to leave me a rating. as lou has already opted out a while ago.

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