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Anthony, Mercedes Technician
Category: Mercedes
Satisfied Customers: 11750
Experience:  MB Tech. since 1997. ASE Master. MB Factory Technician. MB Antique Specialist.
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My 1999 ML 320 threw codes P0170 and P0173 with freeze frame

Resolved Question:

My 1999 ML 320 threw codes P0170 and P0173 with freeze frame LTFT in the 14 percent range and STFT in the -1 percent range. I used MAF cleaner on my MAF sensor and the LTFTs jumped to 20 percent. I have replaced the MAF sensor and the LTFT has dropped to around 6 percent. But the STFT is now around 6 percent (negative, I think, but not sure) and the computer still is throwing the P0170 and P0173 codes. (Engine idle appears to be a bit rougher too.) What is my next most logical culprit? Or is the computer merely taking its time in readjusting to the new MAF sensor? Thanks!
Submitted: 6 years ago.
Category: Mercedes
Expert:  Anthony replied 6 years ago.

Hello Sir or Madam. Welcome to justanswer!


You need to have the adaptation values cleared out of the computer. This cant be done with a regular scan tool. It has to be done with an MB specific tool. The dealer charges a half hour to do this. The codes will return with a new sensor or not until you get the values cleared.

Customer: replied 6 years ago.
But will the adaptation values eventually settle down to normal without being reset? Can I just give it a few more miles, or do the values really need to be cleared? And presumably the trouble codes will stop appearing (after I clear them with my OBD2 tool) once the values settle down, right?
Expert:  Anthony replied 6 years ago.

Ok, if you're at + or minus 10 percent or less your good. Some techs don't reset the adaptation I however do and have been doing so since these airflow sensors started failing at 50K miles often. I have had at my dealership at the time had 5 comebacks from not resetting the values. Once that was done I never had a light again after doing the sensor. Have the values reset. By the book thats the right way.

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