I was wondering if you could give me your opinion about a car issue I am
having. My 1997 E320 with 95k, is having a PO170 error code. It first came
on a couple weeks ago and I had my mechanic look at it.

PO170 corresponds to "Fuel Trim 1" and there are a list of things this could
be. For some reason Mechanic A doesn't think it's the Mass Air Flow sensor
but Mechanic B does. I had a second opinion. I even brought it to AutoZone
to have the code read... and sure enough it reads PO170 and he thought it
could be an O2 sensor.

I've done a little research and from what I understand PO170 can be the MAF
but usually it has two codes PO170 and PO173. My car is not driving
abnormally. I can merge in and out of traffic and I can accelerate smoothly.
Maybe my car is supposed to be more responsive and powerful? I don't know.

The second mechanic I went to practically specializes in Mercedes and his
sister-in-law works with me. He mentioned that in his experience PO170 is
the MAF. But, I was very concerned when it only took him 5 minutes to come
to that conclusion.

Before I go to the Stdealer, I was wondering if you had any experience with
this. I am frustrated with this situation because I am getting 3 different
answers from 3 different good sources.

I posted this question for my nephew it is his car. Any help would be
appreciated

It is definitely the MAF sensor. We had the same problem on our 01 E320. It
would only trigger one side fuel trim error... not both.

My suggestion is use the MAF cleaner and clean out the MAF unit... take it
off the car and clean it well.... do not touch or break the wire inside the
MAF. If it works, then you don't need to buy a new one.

If no change, buy a new MAF. You have to reset the code after you clean the
MAF... same if you replace it.

O2 sensor is easy to diagnose... there are 4 on your car... front ones are
fast changing readings... using OBD2 scanner... the rears on each side are
slow changing... hold accelerator at a higher position and you will see the
reading change slowly... If you got a zero on one... then bad 02 sensor...
but on the scanner, you might misinterpretate it... because some scanners
shows 8 units... just ignore the 4 zeros...

I owned the same model and had the same P0170 code with a Check Engine
light after about 37K miles.

I had dealer check and estimate it - diagnosed MAF. I cleaned the MAF
and it was OK for about a year. But then reoccurred at 40K miles so I
installed a new MAF, bought from www.thebenzbin.com for about $230.

There are two types of MAF - the newer type has a rectangular electrical
and the older style a round connector. Before ordering pull the
connector off yours to see which is installed on your engine. Your's
probably the newer type.

The MAF is simple to install one clamp and two snaps. Wet the rubber
seal so it slides when you install the MAF. Keep everything clean as
possible.
--
© 2007 T.G.Lambach. Publication in any form requires prior written
permission.