Kindly take time to read and help me.
My car is a 2009 C350

I have the check engine light on for a while now.
Have had it reset many times but it still comes back.

The car still seems to run normal, engine temp I think is still almost the same as before. I had my MAF Sensor cleaned using "CRC MAF Sensor Cleaner" few months back, past mechanic "said" he is sure that he installed the MAF sensor back into the car properly.

The computer diagnosis says that:
0746 The Mixture (Cylinder Bank 1) is TOO RICH current and stored.
0750 The Mixture (Cylinder Bank 2) is TOO RICH current and stored.
What does this exactly mean???

Symptoms:
a. Check engine light is on.
b. A "humming/whooshing" sound can be heard INSIDE the car (particularly the front left side) its loud but not very loud. This happens when I'm slowly accelerating from 0-25mph, the sound is also there while I'm "COASTING" (foot off the accelerator) at those speeds. If the car is on PARK, and I press the accelerator, the sound can also be heard, but its not as loud as when the car is moving.

I went to 2 shops:

1. The first repair shop I went to, they said that they are positive my catalytic converters have problems and needs to be changed. (This is a very very expensive repair, and parts are not available yet), they said that the broken ceramics inside the catalytic converters are making the humming/whooshing sound and also causing the check engine light at the same time.

2. Yesterday, I went to the second repair shop for a second opinion, they said that the "Humming/whooshing sound" and the "Check Engine Light" is not related. This means that I have 2 different problems with my car! They asked me to leave the car next week so that they can check for "air leaks or bearing problems" and also check the "catalytic converters"

The shops already charges money just by finding what the problem is. This means that they can check all they want with the car, even on "unrelated parts" and charge everything to me. Hopefully they'd be honest.

On the other hand, if the catalytic converters are really the problem, then they are also freaking expensive to replace for an old car.(is it possible to just totally remove the cats and bypass the check engine light by doing an ecu reflash? cause someone told me this might be possible.)

and lastly, I definitely don't wanna waste my money by changing a wrong part that is not actually causing the check engine light and the humming sound problem.

So what does "The mixture (Cylinder Bank 1 and Cylinder Bank 2) is TOO RICH" exactly pertain to? Pls. help.

Has anyone encountered this problem?
Thanks.

 

bad oxygen sensors. up stream sensors
if cats were bad down stream oxygen sensors is suppose to set off a check engine light with a non efficient cat operation.

read below how to test for exhaust pressure

http://www.tuneruniversity.com/blog/...aust-upgrades/

 

also have your mass air flow sensor retested and your fuel pressure regulator tested

 

Ok, thanks, I'll have them check these parts first before anything else.

We'll see, hopefully its not the whole catalytic converters

 

I have The same car with same error, I chance lanmba sonda, but error persite.

https://mbworld.org/forums/c-class-w204/634654-c350-error-0746-0750-a.html


Any idea?

 

^This.

 

+1

 

Ok, but is no easy this procedure, I think need very specialistyc mecanic!!.

Thank

 

I've dealt with a couple of V6 engines with cat converter problems and this sounds very similar. The cat's should be covered up to 80K miles under the emission system warranty. The 'wooshing' sound is typical for a plugged up cat and is more prevalent when the engine is under load. MB exhaust system is similar to others with 2 stage catalytics so it would appear your first cats are the issue. replacement cats are available, but you'll have to remove and cut up the entire system to replace the cats. It will probably be cheaper to get a new exhaust system. On-line costs look to be $950 or so. Labor should be 2-3 hundred.

 

Can anyone help! How can I resolve this error codes

 

 

 

Hi dear i have the issue in my w204 c300
did you solve the problem of yes please let me know thank youu

 

hi an old tread but did any of you solved the problem?
i have the same problem...

 

I also have codes 0746, 0750, 0292 and 0296.

These came on almost immediately after getting the A/C refrigerant refilled. Not sure if that could be related.

 

hi and did you solve it?

 

i am not surprised that there is no response...

 

TOO RICH BANK 1 AND BANK 2 on 2008 Mercedes Benz C300

I would have your mechanic remove the intake manifold to check if the intake runners are damaged. One of the intake manifold runners came apart once removing the intake manifold throwing a red flag. I decided to bite the bullet and open the intake manifold, which if opened cannot be resealed, to see if there was more damage. Once it was open we found that one of the plastic intake flaps were broken. Replaced the complete intake manifold with vacuum hoses because they were off. No check engine and the responsiveness improved significantly. Would still recommend checking the Air Mass Meter, Air Filter, and vacuum hoses before going this route, but if all of this was done or checked the intake manifold is most likely your issue.

Put a video of the intake manifold flap that broke inside the manifold. It should be secured with the rest of the intake manifold flaps and should be only be allowed to move once the intake runner actuates. It would be difficult to tell if you put a camera inside. So, if you're a shop looking at this I would recommend letting the customer know that you want to open the intake manifold to confirm if it's damaged internally because as I said above the is no going back once opened and the part itself is around $800.

Also, replaced all the fuel injectors at the same time because they are relatively cheap and they have to come off the remove intake manifold. Vehicle had over 170,000 miles and is running like a champ again.

Note for mechanics if this is the issue you will have to tap the new intake manifold to reinstall throttle body due to new intake manifold not coming with it unfortunately. Obviously a bit more of a process so tell your parts guy not to be cheap and get you new aluminum bolts once the intake manifold is tapped to install the throttle body.

Best,
Uli

 

This is a very old thread but I experienced the same after cleaning the MAF sensor on my 2008 C300. The CEL light appeared after driving 15 miles or so and after I cleaned the MAF sensor. I checked the sensor and it was not seated correctly when I reinstalled it. I fixed it but CEL again after 10 miles. I checked again and cleard the ECM DTC code. I then realized that I failed to insert back the secondary air pump intake into the box. It is very easy to miss because it is hidden once you reinstall the cover where the air filters are. Maybe not relevant to your case but just sharing my experience.