GT-ER

I got both of these codes on my moms c240 and I decided to replace the maf as having both o2 sensors go bad at the same time seems highly unlikely. Anyways, a new oem sensor did not fix the problem. I reset the cel and it keeps coming back. What else should I check?

W203E35

P0172 - Self-adaptation of mixture formation for enleanment at partial load for the right cylinder bank is below the permissible limit.
P0172 - Self-adaptation of mixture formation for enleanment at idle for the right cylinder bank is below the permissible limit.

P0175 - Self-adaptation of mixture formation for enleanment at partial load for the left cylinder bank is below the permissible limit.
P0175 - Self-adaptation of mixture formation for enleanment at idle for the left cylinder bank is below the permissible limit.

W203E35

How long has it been since you changed those parts? Did you drive it long enough for the selfadaptation to happen?

GT-ER

I reset the self adaptations with the cel.

GT-ER

unless....am I wrong to think that the adaptation values reset when clearing the cel? I've driven about 25 miles and the cel came back on.

W203E35

Ya, I don't think the adaptation values change when you erase the CEL. I think it should self adapt within 25 miles but I could be wrong. If you're sure the maf is installed correctly I would just keep on driving and see if the CEL goes away. Glyn M Ruck one of the masters of MB owns a C240. Let's see what he has to say.

Glyn M Ruck

You are too rich on both banks. Cancel code & drive 100 miles & report back. The ECU should settle to the new MAF by then - should be sooner. If not we have to look further. It's not a vacuum leak as you are rich.

Are you sure you have fitted a genuine MAF & not an Audi MAF? They look identical.

What mileage? - We might have O2 sensors on their way out. Are you getting any other codes stored?

Rich fuel trim can be the air pump but most likely culprits are O2 sensors & MAF

I presume the air cleaner is clean/new??

GT-ER

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the part number was identical. I also don't have any other codes, yet. It has new airfilters as well. The car has 65000 miles.

GT-ER

CEL popped up again...this time only the p0172 code came up. Assuming Karo is correct that the adaptation values do not reset when clearing the CEL...this may be good news.

If not...what's next? O2 sensors?

W203E35

If you replaced it then soon it will go away. Usually it takes some time. Hopefully soon the 0172 will go away. Do some more driving. The only fix that I'm seeing in STAR diagnostics is to reset the self adaptation and this will just speed up the process. Your adaptation values are bad because you had the malfunctioning maf and o2. Now with the correct one it's a matter of time before everything gets overwritten with the correct values. This is why you lost one code. Now with more driving the other code should get eliminated.

Erasing the code doesn't touch the self adaptation. It just tells the computer "ok I know what the problem is so now stop bugging me" then it comes up again because now the computer says "you saw the problem but didn't fix it". So the more you drive the more adaptations will write the correct values and then will fix the CEL. I believe the CEL should go away on it's own.

GT-ER

I hope you are right...one other cars I've owned the adaptation values would reset when the cel was cleared...I've never worked on MB's though till I bought mine a few months ago.

Glyn M Ruck

Karo is correct.

65K is low mileage for O2 sensors but we don't know how they have been looked after. Have any silicone containing products been used or sprayed under the hood that the engine can ingest? Silicone poisens O2 sensors.

Put on some more mileage seems like one bank is OK already.

P0172 - System too Rich (Bank 1)
P0175 - System too Rich (Bank 2)

GT-ER

Both codes came back today, I've already put about 100 miles total.

Has anyone ever had an issue with the Fuel Pressure Regulator on these cars? I'm assuming it's in the fuel pump assembly?

W203E35

Wait am I reading this wrong?

P0172 - Self-Adaptation of mixture information for right bank of cylinders is at limit value. Enleanment below permissible limit.

P0175 - Self-Adaptation of mixture information for left bank of cylinders is at limit value. Enleanment below permissible limit.

Does this actually mean the car is running lean or running rich?

I think you're running lean.

The only fix with the STAR tool is that is says to check "Hot film mass air flow sensor" (maf). I think something is still up with the maf. I wish you were here in LA. Plugged that bad boy in and rear the voltage of maf and the values.

Right now I'm clueless as to what it would.

P2085 = P0175 With that said have a look at the attached document. It still indicates the problem is your maf.

https://mbworld.org/forums/attachmen...1&d=1303184464

GT-ER

By enleanment they mean that the ECU is trying to lean the mixture out more that what is allowed. The car is running rich and to get it to run normally the ECU must lean the mixture.

It can't be the MAF as I just put in a brand new oem maf. Now I have to check what's next on the list.

W203E35

Ahh, thanks for the correction

Before you have a look at the o2 sensor do you think you might have a vacuum leak?

GT-ER

Vacuum leaks would make my car leaner not richer ( at least I can't think of a way it'll make me richer ). A fuel pressure problem could make me richer though, don't know if it's a common issue with the C240 though. I'll have to wait till next week to even play with the car any further so I won't have any new updates any time soon but any more ideas I'd love to hear.

kwongkk

The system is running rich, means Oxygen content at both sides exhaust manifolds around the O2 sensors are low, computer try to lean the mixture out all the time , long Term fuel trim is negative. You can see the data freeze frame if you get a good scanner.
Possiblities - (1) MAF is bad, OEM sensor sometimes no good. Original cost around $400- (2) Vehicle not in close loop, thermostat stuck open, engine running cold (can remove therostat an check). (3) A bad cooling temperature sensor, though not always happen, you can check sensor resistance when at cold and after warm up. Resistance should be low when engine hot. (4) etc etc
Is the air duct blocked? Try that , remove the air filter, or creat a vacuum leak to see the opposite code come up, such as P0171 - system too lean.

Glyn M Ruck

You would get a P0128 if the thermostat was stuck. However it could be a faulty temperature sensor that tells the ECU that the car is cold resulting in rich mixture. Happens more than you might think

Pull the sensor & check for fouling & proper earth. After that it's exchange new MAF or replace upstream O2 sensors.

GT-ER

Would a faulty water temp sensor make the dash water temp gauge read incorrectly? It seems fine.

Glyn M Ruck

I've certainly known the sensor to be sufficiently out of calibration to effect fuel trim without it being particularly noticeable on the crude guage.

GT-ER

Hmmmm....guess that's next. Thanks my friend.

ff54976

i know its been years since the last post but did anybody figure out what was gone with these codes. I have the exact same codes, put on a oem mass air and nothing. I have live data but i dont know what to look for.

deinarbenz

h

Alswag

Usually these codes lead to a faulty MAF, but it really could be caused by anything in the intake/exhaust system that's taking a ****. Depending on your mileage, it might be time to replace your O2 sensors. Usually they're on borrowed time after about 160 000 km's (100 000 miles).