Question about 2003 Mercedes-Benz C-Class

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C200 Emission Problems

Hi, I have a 2003 Merc C200. The emissions are really high but my mechanic is convinced that it is not the CAT but an electrical problem. We have replaced the front oxygen sensor and the temperature unit but to no avail. He says that the CO levels are too high for it to be a CAT problem. He has put through a few petrol washes to clear the engine of any debris that may have built up, but still too high. Any suggestions would be greatly appreciated.

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Hello,good day,they already replaced some parts,but same problem,better to send your car to a dealer to diagnose with proper tester,they can evaluate your engine condition for emission test,also ask if you can get a copy of record,specially fault code,freeze frame data criteria,can be presented to emission officer,ty

Posted on May 12, 2009


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You may need a mechanic. At least a shop manual.
The catalytic converter code means the computer does not think the cat is working right based on input from the O2 sensors. That data would need to be checked out and verified along with a temp scan of the cat itself.
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What is wrong with the car it shows me p0432 code main catalyst efface below threshold (bank2), how do I fix it cause the engine light goes on and stays on?


The code means what it say. The car computer compared the data on amount of air/fuel injected in cylinders with the emission O2 reading from the Oxygen sensor in the air intake (the one after cat converter), and decided that the catalytic converter is not doing its job because emission is too high.

In some case the problem is occasional. Try resetting codes by disconnecting battery terminals (make sure you have stereo code if needed).

If the code comes back, then there are several parts to be tested before replacing cat converter.

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Sensors in the air intake and air intake itself must be tested, check MAP sensor and intake structure for leaks. Replace air filter. Check the vacuum for leaks. Check IAC. Check O2 sensors.

If there is no problem under the hood, check the state of other parts comprised in the exhaust system and eventually replace the cat converter.



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High emisions new cat new sensor


High emission are often consequence of engine problems. In that case the new cat converter or exhaust and new oxygen sensors will not help.

High emission from engine occurs because of many different reasons, main causes are:

Electronic injection problems:

Do an OBDII scan to find out if there are error codes. If there are no codes check injectors sensors in the air intake (MAF and IAC), check vacuum for leaks. Clean throttle body. Check EGR, IAC, PCV systems.

Engine internal problems:

Do a compression test to find problems associated with engine faults (eg.piston rings, head gasket, valves).

Also make sure that spark plug, fuel and air filter have been replaced. Make sure that there is no misfire or distribution problem.



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