Question about 2006 Mercedes-Benz ML-Class

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Catalytic convertor replacement on Mercedes Benz 430 ML

I have a Merc 430 Ml 2001 model. The two catalytic converters have blown however Mercedez want to charge me a fortune to replace the two cat's. Replacement value is approximately 26% of the price of a brand new engine! Merc have warned me that I have to replaceme them otherwise it will damage my engine. In addition they warn me that the engine management system will not work as there are 2 sensors on either side of the cat's.
I simply want to cut them off and replace with a normal exhaust (straight pipe). I want to know if I can.

Trevor James (South Africa)

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  • Anonymous Mar 25, 2014

    Looking at 99 s240 with 4.2 which has an exhaust odor kind of like burning rubber. How many cats is this car equipped with has it has duals? Thinking about just writing this one off.



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You could probably do this, but you're going to be running with a permanent check-engine light. The twin O2 sensors on each exhaust pipe are for emissions reasons. Your primary (pre-cat) O2 sensors help the engine determine how much fuel to inject, based on reading the level of unburned oxygen in the exhaust stream. Your secondary O2 sensors (post-cat) are there to provide a similar reading. The car's computer then compares these two values to determine the efficiency of the catalytic converters. If the comparison strays outside an accepted range, the computer trips a fault light.

If you have emissions testing or regulations to that effect where you live, you will not pass inspection. In addition, if you have smog laws that mandate cats and other smog equipment, you could be risking a huge fine if you're found to have removed them. I'd check with an auto parts store about getting some generic universal cats (make your choice based on the length of the cat assembly and the diameter of the inlet and outlet pipes). These are generally far less expensive and work just fine.

On a side note, are you positive that the cats are bad? If you're tripping a fault code for a failed cat, it could be that one or the other of the O2 sensors are bad and causing an indicated cat malfunction. I'd have at least a couple other places look at the car and see whether it's the cats or the secondary O2 sensors before shelling out the money for cat replacement.

Posted on Jul 21, 2008


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