Hi,

I have a 2011 W212 just replaced engine mounts; the mounts themselves are working fine. The problem is that a day after I picked up the car, I noticed gas smell in the cabin, and later the engine light came on, used OBD2 scanner to read, it appears that both "bank1" and "bank2" are too "rich".

I am not sure if this is just coincidental or something got broken during the process of replacing the mounts. I understand that the shop may have to take off the exhaust where the O2 sensor has to be disconnected and reconnected.

Would anyone has experience in this?

Thank you in advance.

 

Forgot to mention, it is P0172 and P0175 code.

 

I'd go back to the shop with this info. Sounds like they may have disconnected or damaged something. The pre-cat O2 sensors will throw those codes. Have them check all air flow sensors, etc. and O2 connectors.

 

maybe a silly question, what happens if the O2 sensor was not connected? would it throw a P0172 code or it would be something else?

 

So I cleanned the MAF and throttle body, ran a Freeze Frame on my OBD scanner, I am wondering if anyone can give me some insights here:

PID Description Value

© BlueDriver 2019
Freeze Frame Report - 2011 MERCEDES-BENZ E-Class 3.5L V6
02 DTC that caused freeze frame data Trouble Code P0172 triggered Freeze

Frame.
02 DTC that caused freeze frame data Trouble Code P0172 triggered Freeze Frame. Code Def: System Too Rich Bank 1
03 Fuel System Status System A: Closed loop - using all oxygen
sensor(s) as feedback for fuel control
System B: Closed loop - using all oxygen
sensor(s) as feedback for fuel control
04 Calculated Engine Load Value 35.7 %
05 Engine Coolant Temperature 98 °C
06 Short Term Fuel Trim Bank 1 4.7 %
07 Long Term Fuel Trim Bank 1 -9.4 %
08 Short Term Fuel Trim Bank 2 8.6 %
09 Long Term Fuel Trim Bank 2 -11.7 %
0B Intake Manifold Absolute Pressure 38.0 kPa
0C Engine RPM 793 rpm
0D Vehicle Speed 6 km/h
0E Timing Advance for #1 cylinder 11.0 °
0F Intake Air Temperature 30 °C
10 Mass Air Flow Rate 7.00 g/s
11 Absolute Throttle Position 13.3 %
12 Commanded Secondary Air Status 0
1F Run Time Since Engine Start 805 seconds
23 Fuel Rail Pressure 380 kPa
2E Commanded Evaporative Purge 0.0 %
2F Fuel Level Input 72.9 %
33 Barometric Pressure 97 kPa
42 Control Module Voltage 14.135 V
43 Absolute Load Value 24.7 %
44 Commanded Equivalence Ratio 0.999 λ
45 Relative Throttle Position 2.0 %
46 Ambient Air Temperature 7 °C
47 Absolute Throttle Position B 12.9 %
49 Accelerator Pedal Position D 5.5 %
4A Accelerator Pedal Position E 5.9 %
4C Commanded Throttle Actuator 2.7 %
56 Long Term Secondary Oxygen Sensor Trim Bank 1 -0.8 %
58 Long Term Secondary Oxygen Sensor Trim Bank 2 -0.8 %

 

ECU would throw a fault on Lambda sensor being in open circuit. These are extremely well monitored.

Your engine is reporting unburnt fuel.

Your issue is gonna be something like a leaky injector or bad spark ignition. Perhaps not enough air is able to enter... odd.

Since this happened after dealer visit then more likely poor ignition than an injector got bad over night. Double check your plugs and coils....

 

thank you for the suggestion.

I replaced all spark plugs not long ago...the thing is that both banks reported "rich" at the same time, I would imagine if anything wrong with one of the plugs or injectors, then only one bank will report code?

 

Yes, you're right: engine is rich across both cylinders banks. So less likely ignition related unless low voltage is available.

- FUEL : "fuel pump gone wild"... read pressure??

- AIR restriction would cause rich mixture.... MB is famous for intake plenum issue. Check rods, diaphragms??

 

Thank you.

I replaced my air filter at the same time I replaced the spark plugs, so maybe I will look at the fuel management. Wondering if that can be seen from the OBD scanner.

I went and drove the car for a few minutes and the logged the data. It appears that bank 1 is consistently higher percentage than bank 2, between 5-10%, for both short term and long term trim, what would cause that?

 

Replacing the engine mounts requires lifting the engine slightly to take the weight off of the mounts on either side of the engine. At the back of your engine, the intake plenum has flap control actuators that open and close to create torque under different loads and different speeds. IF, in raising the engine, the shop carelessly raised it without checking clearance of the plastic actuators on the back of the intake, they could have been crushed or damaged. Check against the firewall for any damage to those parts.

BTW, as long as long term fuel trim (LTFT) and short term fuel trim (STFT) are in the range of -25% to +25%, you should not get a code or CEL.

 

This should give you a better understanding.

 

Never mind (ie. ignore STFT) the short term trims... We already know what LTFT is saying.

Now we're after finding causes of your rich mixture being compensated by lean injection...

> Look at your ECU live data for oddities with a MB specific scanner... (not an Autozone generic tool). This simple step will speed up finding something obviously weird we have not thought of. A missing sensor would pop a fault on a good scanner. So nothing's missing - Best guess here pre-cat upstream sensors telling stories to ECU.

> Run a physical inspection around engine bay: anything strikes you? See if the plenum rods are loose or connected...

> How does the engine run with this rich condition.... any misfires??

> Do you trust the supply-chain genuine quality of Lambda sensors?? Take some time to observe what value do they read: upstream B1 vs. B2 ?

🤞

 

MBwing,

What engine is yours ?
Find your ECM wiring diagram and see, if your engine is still using the same 4 pins oxygen sensors front and back ?
If so, techy may have connect them wrong, as is opposite wrong.
This is assuming the 2 connectors design allow such mistake. Usually MB will use diffent type of connector to avoid such silly mistake.
However I think you are using M272 being a 2011 model year and I am blind on this engine.

I am out of town now for 2 weeks, so I can't access my WIS/EPC.
If M276.9 engine, it uses 6 pins for front wide band oxy sensor and 4 pins for narrow band rear oxy sensor, so it can not be installed wrong.

 

If the upstream and downstream oxy sensors have different connector and can't be installed wrong................

The downstream narrow band oxy sensor commonly a 4 pin one.
2 pins for heater and 2 pins is the actual voltage output of the oxygen sensor CELL. This cell is like a mini battery based on heat, so ECM does not power the downstream CELL, only the heater.
I think if the downstream oxygen sensor get disconnected or not properly clicked-connected, you may get a heater code DTC.
Since I do not trust trust OBD2 reader like BlueDriver, you best get a proper scanner with MB compatible software to read more DTCs when and if there is any.

 

thank you everyone. much appreciated for the input.

My car is a 2011 W212 E350 4Matic

So I cleaned the MAF as it seemed that it was usually the first thing to do when having similar issue. I then cleared the engine light. Today I drove for about half an hour, mostly on high way. I logged the bank1 and bank2 STFT and LTFT, as in the attachment. The stable portion of the data essentially is when I was on the high way. The data seems to be telling me:

1) both bank1 and bank2 are within the limit when cruising;
2) for some reason, bank1 LTFT is consistently higher than bank2 for a few percent, I wonder what would cause that
3) there are spike/drops along the way, not sure if this is normal or this is due to the data acquisition process, e.g., reliability from the OBD2 bluetooth device





So after this morning's drive, no engine light came back on. I will continue to observe. I wonder what caused the engine light originally.

 

As @S-Prihadi said, "Since I do not trust trust OBD2 reader like BlueDriver, you best get a proper scanner with MB compatible software to read more DTCs when and if there is any."

Bluetooth is probably not reliable for precision datalogging. Get a and try again for comparison. You may have solved your problem this time, but you WILL need the scanner again. BlueDriver is OK for emergency code resets or generally identifying an ambiguous dash light, but don't rely on it for diagnostic problem solving.