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2006 CLK 350
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P0170 DTC Error Code ===> If MAS is good then check for Air Leaks

An air leakage around the MAS will also cause the P0170 error code even with a good MAS!!!

This air leakage includes a bad seal (O-ring should be replaced if worn, etc.) before and after the MAS, and leakage around the Air Cleaner neck as well. Also make sure all air cleaner hose clamps are screwed down tight!

MAS generally start going bad around 60,000 miles but your's is only 20,000 miles, so that should not be the problem unless it was not an OEM Mercedes MAS. Where did you buy the MAS from? Dealer or eBay????

My car was getting a P2188 and P2190 error code which is engine too rich on Bank1 and Bank2; sometimes only the Bank1 error code appeared. The Dealer said the MAS was bad... I was ready to replace it until I happened to bring the car to a MBZ Club tech session held at the Park Ave Mercedes in Palo Alto and they found the problem to be a misaligned air cleaner!!! As it turns out, this aircleaner on the CLK has a very tight neck and requires a pretty hefty pounding on the rear portion to slam home and seal the neck to the MAS!!!

Look at the Long Term Fuel Trim data values if your Scanner will record the data. If the LTFT exceeds 9 - 10 % (rich), it will generate a P0170 error code. Sometimes a long drive on the highway for an hour or two will reduce the value but a lot of City driving will slowly increase the % value. A leaky fuel injector or leaking cold start injector/valve will also cause a rich condition. If very Rich you can smell raw gas from the exhaust... and if the raw gas gets really bad, it can kill the CAT converter which will start to smell like Rotten Eggs!!!

Good Luck.. :)

The Short Term Fuel Trim (STFT) should generally average to Zero %.
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