Hey All,
A few weeks ago my engine started misfiring. I got a CEL code for misfire cylinder 5 so I went ahead and replaced all the spark plugs and had to replace the ignition coil on cylinder 5 because that was faulty. The next day I got P0172, P0175 Bank 1 & Bank 2 too rich codes. Car was driving perfectly fine so I didn't get the chance to do anything until this past weekend. I changed the air filters, pulled out the MAF and sprayed it with MAF cleaner. I noticed on the Engine Cover/Air Filter housing the rubber seal that sits over the MAF has a tear but doesn't seem like its enough to cause air loss.

Anyways, after about 20 miles of driving the P0172 P0175 codes came back. This time the car does seem slightly sluggish when accelerating but it goes away after giving some gas. I did notice that when I take my foot off the pedal where the speed is < 15 MPH and rpms are between 1400-1000 the car slightly jerks.

I have a simple OBD 2 scanner and pulled the freeze frame data (below). I thought about replacing the MAF but I'm not sure if it's bad and don't know much about working/diagnosing cars. I don't really know what to make of the data though so any help would be much appreciated.


2009 ML350 4matic ~97k miles


Freeze frame data:

DTCFRZF P0172
FUELSYS1 CL
FUELSYS2 CLETC (F) 192
SHRTFT1 (%) -4.7
LONGFT1 (%) 0.8
SHRTFT2 (%) -4.7
LONGFT2 (%) 2.3
MAP (inHg) 11.2
VSS (mph) 0
SPARKADV(*) 10
IAT (F) 61
MAF (lb/min) 0.804
TP (%) 12.5
AIR_STAT OFF
RNTM (sec) 699
EVAP_PCT (%) 0.0
FLI (%) 13.7
BARO (inHg) 28.9
VPWR (V) 14.041
LOAD_ABS (%) 33.3
EQ_RAT 0.999
TP_R (%) 1.2
AAT (F) 39
TP_B (%) 12.5
APP_D (%) 6.7
APP_E (%) 5.9
TAC_PCT (%) 1.6

 

You probably damaged the seal replacing the eng. cover. That is why you are getting the fuel trim codes. It must be replaced.

Then the codes must be reased.

 

Thanks! I went ahead and installed a new seal today and cleared the codes. Any idea how many miles it takes for the reset? I've heard 100 miles.

 

 

Why don't you just erase the codes with your scanner?

 

I erased the codes using my scanner. After about 20 miles of driving the codes came back. Any idea what I should be doing next?

 

I erased the codes using my scanner. After about 20 miles of driving the codes came back. Any idea what I should be doing next?

Edit: Sorry about the double reply. Don't know why it did that.

 

Well then there is still a vacuum leak somewhere.

 

I thought vacuum leaks caused running too lean, can it cause running too rich also?
How would I check for vacuum leak?

Any idea if faulty MAF can cause these codes? I am about to reach 100k

 

Lean condition means too much air or not enough gas. The ECM can only correct rich or lean by shortening or extending the injection time of the injectors.

 

Thanks for the pdf. I thought the codes were for rich condition since the scanner was saying so.

Drove for 20-30 miles on Thursday and the CEL went away. Not sure if the gasket fixed it but the codes still show up on the scanner. Any idea what that is about?

I looked around and couldn't find a hose leaking. I did find my power steering pump leaking so I'll have to get that fixed. Can that cause these codes?

 

If the CEL went away the code will erase itself.

 

Just as a data point, I have been battling a recurring check engine light after doing some routine maintenance, namely a transmission fluid flush, air filter elements, and spark plugs. (2010 ML350, 59K miles). I would get P0172 and P0175 codes (self adaptation of mixture formation enleanment at idle for the right (and left) bank is below the permissible limit. I could clear the codes, go drive 20-ish miles and everything is fine, but as soon as I'd get off the freeway and back to idle, it would throw these two codes.

Tonight I put the car up in the air to make sure I didn't mess up any of the O2 sensor connectors (I didn't), and then decided to check the seal on the air cleaner housing to the MAF. I recall when I pulled the air cleaner housing it was a real struggle, but it finally came off. I didn't think too much of it at the time but on further inspection this evening I'd pulled the wire 'bail' that clips across the top rear of the air cleaner housing. Duh, big air leak at the MAF. None of my previous M272/273 cars have had this wire bail, it was a new gotcha for me.

Bail back in place:

 

That is the indication you've seated it properly. The air filter housing on my GL was hard to seat properly. It would seem like it was in place, but if the wire bail couldn't easily be pulled over the lip, the housing wasn't fully seated and error codes would result. My ML is much easier for some reason.