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1999 E320
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372 Posts
Discussion Starter · #1 ·
So I plugged in my OBD2 reader just to see if anything was wrong, and what do you know an error code was read. Its code is P0170 Fuel Trim Malfunction (Bank 1). I've searched and read a few threads about this, so I went out and bought some MAF cleaner and cleaned it- codes still there. There is no CEL light on. I went through my service records and found the following:

Fuel filter and spark plugs were replaced about 15,000 miles ago

MAF was replaced about 20,000 miles ago

Both O2 sensors (ATWC and BTWC) were replaced about 24,000 miles ago

Any ideas guys? Is this a big problem, or just an annoyance?

BTW I just found out that the previous owners had been letting the mechanic put in Havoline 5W40 Synthetic oil for every oil change. Could this be a problem? Thanks!
 

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1994 E320 Wagon,1999 E320 Wagon,2000 E 320 Wagon, MGB Track/Rally, ,1988 300E ,more....
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6,019 Posts
No cel

it is just a pending code.Could clear itself after several drive cycles or if it falls out of range further will trip the light fantastic.For now don't worrry.
Oil don't worry just get the correct stuff in next change.
When you do it yourself:thumbsup:
:bowdown:
 

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1922 Ford T no OBD, no ECU, no SCN
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37,844 Posts
Years ago, before I bought a scanner I had MAF malfunction with CEL.
After replacing the MAF I cycled the starting procedure 7 times and CEL went off.
10 second procedure.
 

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'01-E320 & 02-ST2
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31,631 Posts
So I went ahead and cleaned the MAF. Today I checked and the code is gone.
I assume this is related to your 99?

You actually have FOUR O2 sensors, so that may still be an issue. Also, on the V engine configuration a fuel trim code on only one bank is almost never the MAF, more likely an O2 sensor, cat, vacuum leak, etc. on the bank that is triggering the code

All that said, if the car is running fine you can always still have a pending (transient) code and the key is to mostly ignore them unless they trigger a cel.

The only time pending codes are really (potentially) meaningful is when you have a symptom or two you're trying to chase down. Otherwise their usefulness is mostly limited to increasing one's post count on internet forums. ;)

Take care and enjoy the ride,
Greg
 

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2006 CLK 350
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1,133 Posts
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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