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I've been struggling to resolve a check engine light issue…

Customer Question
Hi Pearl, I've been...

Hi Pearl, I've been struggling to resolve a check engine light issue for a while now. Have tried changing out several components, yet still ticks back on after a few hundred miles.

Mechanic's Assistant: Does the light stay on, or does it blink?

Stays on

Mechanic's Assistant: What is the model/year of your Mercedes?

2004 C230 Kompressor sedan

Mechanic's Assistant: Are you fixing your C230 Kompressor yourself? What have you tried so far?

I've mostly taken it to the dealer since I have a good relationship with the foreman and service advisor. have also have an outside mechanic run the codes as well. Last items replaced the the sender unit for a leaking crankcase vent hose, and a month later removed and replaced injector o-ring seals, and removed and replaced vacuum pump.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Yes, that it is a manual transmission, not automatic

Submitted: 2 months ago.Category: Mercedes
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Customer reply replied 2 months ago
The code that was last given to me when this all begin was P201C-001 - Self adaptation of mixture formation, The mixture is too rich in the part load range [P0172] ECM.
Answered in 2 hours by:
3/26/2018
Mercedes Mechanic: Matt, Engineer replied 2 months ago
Matt
Matt, Engineer
Category: Mercedes
Satisfied Customers: 23,199
Experience: Mechanical Engineer with 23 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello and welcome to Just Answer

there's a couple of possibilities:

Incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will be leaving the car constantly ' on choke' and not reducing the fuelling as the engine warms - so unplug the sensor and clean the contacts on both sides with some switch / electrical cleaner (not WD40) and inspect the wiring for any signs of damage to the insulation especially where it runs over other components and through the bulkhead- if this doesn't help consider replacing the sensor as they're not expensive
Check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

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Mercedes Mechanic: Matt, Engineer replied 2 months ago

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Mercedes Mechanic: Matt, Engineer replied 2 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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