[dustinsroberts]

I have a 2005 c230k with 77k. I started getting a cel a couple of months ago. Changed the maf and spark plugs but the codes keep coming back. Below are the results from the scanner.

P0170
P0171
Bank 1 lean

Calculated load = 30.19%
Short term fuel trim bank 1 = 3.88%
Long term fuel trim bank 1 = 13.27%
Intake map = 78.0KPa
Throttle position = 20.39%

Can anyone offer suggestions on what I can try next? I was getting at least 32mpg before and now 26-28mpg.

Thanks!

 

[Check Codes]

You don't mention mileage, but O2 sensors can trigger those and they are 100K items.

The little vacuum tee at the purge valve (marked MOT) can also crack and trigger this code, but I'd encourage you to inspect/replace every vacuum line under the hood as they will frustrate you as they fail one by one due to age.

Good luck.

 

[dustinsroberts]

It has 77k miles. Where would one find the purge valve? Is there an online source that lists all the vacuum lines that can be replaced?

 

[dustinsroberts]

Any suggestions?

 

[Andrzejek]

What brand MAF did you install? Replacing all vacuum lines is a good bet.

 

[eric242340]

What brand MAF did you install? Replacing all vacuum lines is a good bet.

If the MAF is not OEM then this is not a way to go.

 

[Andrzejek]

Yes and no. I replaced mine over six months ago with an aftermarked unit and the car runs great. Fuel trim (long/short) runs close to zero. No OBDII codes. The MAF cost me under $30. Not sure how long it will last, but if I get a few years out of it, I'll be happy.

 

[BizRob30]

I had this same problem, I replaced with Bosch and still get same two codes.... gas mileage is 20 city / 27 hwy. Not too bad but the damn CEL alarm is driving me nuts. I guess vacuum lines are next on my list to check

 

[Andrzejek]

You might also want to check/replace the two O2 sensors.

 

[BizRob30]

You might also want to check/replace the two O2 sensors.

If it were the O2 sensors, don't they have their own codes? The only ones I am getting are MAF

 

[dustinsroberts]

If the MAF is not OEM then this is not a way to go.

I bought this MAF Cardone Reman/Mass Air Flow Sensor (74-10123) | 2005 Mercedes Benz C230 4 Cylinders 1.8L SFI DOHC SC | AutoZone.com

I sure would like to know where Andrzejek got his MAF. The one I purchased at Autozone was around $350.

 

[TexFinn]

Autozone

There is one of your problems. Especially since the unit you bought is a reman.

If you want to change the MAF, take the unit you have now back to AZ to get your money back. Then get yourself a genuine MB one from AutohausAZ for just about the same price.

https://www.autohausaz.com/search/[email protected] & Air System&[email protected] Mass Sensor

 

[Check Codes]

There is one of your problems. Especially since the unit you bought is a reman.

If you want to change the MAF, take the unit you have now back to AZ to get your money back. Then get yourself a genuine MB one from AutohausAZ for just about the same price.

https://www.autohausaz.com/search/[email protected] & Air System&[email protected] Mass Sensor

Three things: I would second the above. Who knows what actual sensor they put in there. You can always start with the purge valve and vacuum lines and if the codes remain, then do the MAF exchange.

And: The purge valve is near the fenderwell and typically marked "MOT" on top. You can clean it as well (but dirtiness won't affect a FT code) and you can key off the DIY in the W210 section stickies, pretty much the same part, you don't disassemble it, just remove it and blast it clean, dry and put back.

Finally: O2 sensors when old/tired can cause sufficient FT variations to trigger the CEL and that can happen well before their own circuitry is bad enough to trigger the O2 specific codes. 77K seems a little early for O2 sensors, but a failing MAF can raise exhaust temps, which can shorten their lives (as well as the cats...and clogging cats can also adversely affect FT).


Good luck.

 

[Andrzejek]

If it were the O2 sensors, don't they have their own codes? The only ones I am getting are MAF

P0170 code is "fuel trim" right? A "closed" fuel circuit is controlled by the O2 sensors. P0170 is thrown when the O2 sensor can't keep the exhaust levels within specs.

 

[BizRob30]

P0170 code is "fuel trim" right? A "closed" fuel circuit is controlled by the O2 sensors. P0170 is thrown when the O2 sensor can't keep the exhaust levels within specs.

Is this just for the P0170 code... I am getting that one and the P0171 code as well. Everything I read suggests that both codes mean a bad MAF. I replaced the MAF with Bosch and still get codes. Starting to wonder if I am the 1% who don't have a bad MAF and have another problem instead.

 

[eric242340]

Three things: I would second the above. Who knows what actual sensor they put in there. You can always start with the purge valve and vacuum lines and if the codes remain, then do the MAF exchange.

And: The purge valve is near the fenderwell and typically marked "MOT" on top. You can clean it as well (but dirtiness won't affect a FT code) and you can key off the DIY in the W210 section stickies, pretty much the same part, you don't disassemble it, just remove it and blast it clean, dry and put back.

Finally: O2 sensors when old/tired can cause sufficient FT variations to trigger the CEL and that can happen well before their own circuitry is bad enough to trigger the O2 specific codes. 77K seems a little early for O2 sensors, but a failing MAF can raise exhaust temps, which can shorten their lives (as well as the cats...and clogging cats can also adversely affect FT).


Good luck.

At this sort of mileage it would be very rare for it to ba a 02 sensor, so I would check everything else before suspecting this. And 02 sensor failure does have a seperate code.

 

[eric242340]

Is this just for the P0170 code... I am getting that one and the P0171 code as well. Everything I read suggests that both codes mean a bad MAF. I replaced the MAF with Bosch and still get codes. Starting to wonder if I am the 1% who don't have a bad MAF and have another problem instead.

Start looking for vacuum line leaks.

 

[eric242340]

P0170 code is "fuel trim" right? A "closed" fuel circuit is controlled by the O2 sensors. P0170 is thrown when the O2 sensor can't keep the exhaust levels within specs.

Which would indicate that the problem is prior to 02 sensors and not caused by 02 sensors.

 

[BizRob30]

Start looking for vacuum line leaks.

Thanks, I'm on it.

 

[Andrzejek]

Which would indicate that the problem is prior to 02 sensors and not caused by 02 sensors.

That is true, but the O2 sensor is also a part of the loop and most mechanics will check it's operation on vehicles with a "fuel trim" problem.