My car had done only about 37K when the check engine light came on so a
failed sensor was unlikely. Code PO170 didn't describe the exact problem
so I paid the dealer to diagnose and estimate the repair and its cost -
MAS about $550 - $600. (On line part price $260.)
Then I thought about the project and decided to first try cleaning the
MAS and replace it DIY if cleaning failed.
My E320's MAS has two pieces: the larger 3" x 4" "stovepipe" housing and
the sensor itself which screws into the side of the "stovepipe".
Removing the "stovepipe" is easy. Then one removes the sensor from the
I used an old fashioned (smoker's) pipe cleaner to simply clean the
sensor's wires - very, very carefully, in daylight.
I didn't use any solvents for there are no petroleum deposits on the sensor.
Cleaning worked, there's been no further messages.
I cleared the codes with my code reader.