Question about 2006 Mercedes-Benz ML-Class

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ML430 Catalytic Converter Model:2001

Dear J Del, Tks for your reply. Much appreciated.
In South Africa we have no laws governing emissions.
Engine "fault light" does not come on. Exhaust is blowing & local repairmen (x2) have confirmed slits/holes in both cat's. The one **** they have tried to weld closed.
No generic cat's are available in South Africa. I have been on to a website in USA (convertergeek) and can find generics.
Local exhaust repairman says that he can cut out the cat's, then weld back the sensors either side of a new "staight pipe" and he says fault light will the not come on.
So, I am a little nervous about this option as I don't know if this will effect the performance of the car.
On the flip side, Mercedes have warned that without their approved cat's the engine management system will screw up performance of the car and they will not be able to service the car with their electronic system in the future.
Do think the repairman can cut out cat's, then weld back the sensors on either side of the replacemnet straight pipe as he has suggested I do?

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j_del
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SOURCE: Catalytic convertor replacement on Mercedes Benz 430 ML

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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ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

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Common Misdiagnoses

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Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

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* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

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* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

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* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
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Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem



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Replace it.


ACTUAL DIAGNOSTIC:

Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.

Symptoms

* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
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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.

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