Problems with the catalytic converter on your Mercedes, or any vehicle for that matter, are often more difficult to deal with than most drivers realise because it is illegal to tamper with a catalytic converter in any way. This means it is illegal to attempt to fix your Mercedes' catalytic converter by any means other than having an approved certified mechanic replace it.
There are both federal and state laws governing the removal and replacement of catalytic converters on vehicles. The noise your catalytic converter is making indicates a problem that may cause your Mercedes to fail an emissions test or land you a number of federal fines from the Environmental Protection Agency if not handled properly. It is only legal to remove it if the noise is affecting its function.
Check the warranty. Your Mercedes may not be covered by the federally mandated Environmental Protection Agency warranty. Federal law emissions warranty specifies that if your car was manufactured before 1996, the catalytic converter is still under warranty only if the car has less than 50,000 miles on it. If the car was manufactured after 1996, the car is legally required to have more than 80,000 miles on it or be more than eight years old to be out of warranty.
Some Mercedes vehicles have documented issues with the catalytic converters. Mercedes reached a settlement with the EPA to extend the emissions warranties on these vehicles.
Take your Mercedes to the dealership, or a mechanic who regularly handles these cars, and have the catalytic converter tested. You will need to go to a mechanic who is familiar with the car's exhaust system requirements and has access to original equipment manufacturer, or OEM, exhaust parts. The converter used to replace your Mercedes converter must be identical to the original Mercedes catalytic converter.
If your car is still covered by the federal warranty, it will need to be taken to the Mercedes dealership.
Have the mechanic thoroughly document the problem with the converter, then, if necessary, replace it with an identical new converter. Documentation of the problem is a legal requirement if the converter needs to be replaced.
Since tampering with converters is illegal, your noisy converter will probably be replaced. If the converter is still functioning, the mechanic is not legally allowed to remove it.
Make sure the mechanic also fills out a warranty card as required by federal law. Save a copy of everything for your records in case of emissions inspection problems at a later date.
You may have to take additional measures if you live in California. However, your mechanic should be able to handle the entire process for you.
Tampering with or removing a catalytic converter is illegal. Catalytic converters must be handled by professional mechanics who can document and verify their work.