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MB Paul
MB Paul, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4317
Experience:  Qualified Mercedes Benz Diagnostic Technician - 20+ years experience - Workshop Foreman for Mercedes
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What do error codes on a 1999 ML320 of P0170 and P0173 really

Resolved Question:

What do error codes on a 1999 ML320 of P0170 and P0173 really mean. Changed to new bosh plugs but continue to get the same codes after changing plugs. Have changed the air filter and put two cans of Lucas fuel injector cleaner in the tank - but continue to get these two error codes. Your help please!
Submitted: 7 years ago.
Category: Mercedes
Expert:  MB Paul replied 7 years ago.

These 2 codes relate to the self adaptation being out of limits - the ECU monitors the air/fuel ratio & tries to compensate for any errors. When it can no longer compensate it stores these codes.

It could be anything in the air/fuel system causing these codes but the most common problem is with a faulty MAF (air mass) sensor. When the MAF goes bad it sends an incorrect signal to the ECU & the fueling goes out of spec.

The intake should first be checked for any air leaks which could also cause this problem.

The MAF readings can be checked on a diagnostic tool with access to actual values, but even then the MAF is usually ok at idle when the test is carried out & the only sure fire way to see if this is at fault is to replace the MAF or swap it with a known good one.

It could also be down to poor fueling from the injectors or incorrect fuel pressures, but in reality this is far less common.

Best regards, Paul
Customer: replied 7 years ago.
Can you supply a part number for the MAF sensor, and describe specifically where it is located? I just had the air intake off when accesing the spark plugs and saw no obstruction in it.
Expert:  MB Paul replied 7 years ago.

The MAF is located in the intake after the air filter, either in the pipe or at the end of the pipe before the throttle body. It should have a multi plug connector connecting onto it with around 5 pins.

Here is a link to the MAF - there are many option aftermarket but I would always stick with Bosch as these are OEM parts & will perform as intended. I have known some cheaper parts that are very poor quality & in some cases worse than the faulty one you are replacing!!

MAF sensor

Best regards, Paul
MB Paul and 3 other Mercedes Specialists are ready to help you
Customer: replied 7 years ago.
Thank you very much. I have a 1999 E320 also. Appears the MAF sensor is the same on both from the infromation I can find. I will switch out the two and see if the error code goes with the sensor. Unfortuntely my wife has the E320 today so can't readily make the exchange at this time.

Would you mind supplying an email address where I can follow up with you later.

If so, I will gladly accept your answer for payment authorization!

Best regards.

Expert:  MB Paul replied 7 years ago.
Hi Glenn,

All V6 engines use the same MAF so swapping over with your E320 is a perfect test!

We are not allowed to communicate outside of JA, hence why your email was X'd out.

Just reply on here & I will pick up any replys from you & respond ASAP - bear in mind I am in the UK so if its too late I may have to reply to you tomorrow!

Best regards, Paul