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1998 E320
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52 Posts
Discussion Starter #1
A couple weeks ago my CEL popped up, so I went to AutoZone to have the code checked and the guy said it was P0173. I ended up going to Harbor Freight to pick up a cheap OBDII scanner for $40 so I could read and clear the codes myself. When I cleared the codes and restarted the car, the CEL would immediately come back but now the codes are P0170 & P0173 which should be MAF or Air Filter. I changed the filter out, which was pretty dirty, and the CEL stayed off for a couple days.

It's doing much better now, but every couple days the CEL will pop back on and just give the code P0173. I bought some MAF cleaner and in the next couple days I'm going to take of the MAF sensor and see if cleaning it will help. Has anyone else had a problem like this? Does it sound like an O2 Sensor, maybe the driver side due to the Fuel Trim Bank 2? I'm starting to log when the CEL goes pops up so I can maybe figure out what's causing it. It seems to trigger the CEL when I'm driving slow or at a low speed.

Here is my Freeze Frame Data from the OBDII Scanner:

DTCFRZF P0173
FuelSys1 CL
FuelSys2 CL
Load_PCT(%) 22.0%
ETC(F°) 183°
SHRTFT1(%) -1.6%
LONGFT1(%) 27.3%
SHRTFT2(%) -0.8%
LONGFT2(%) 30.5%
MAP(inHg) 12.4
RPM(/min) 525
VSS(MPH) 4 mph

Thanks in advance guys!
 

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use a quality scantool to retrieve the fault code. if i where you, i would just pay a mbz tech, and independent, with and sds, get the correct fault code (s)and also get the adaptation value,(fuel mix) ,if you have an air leak in the intake system, you will get a po170 series code. also,have the fuel pressure tested; you may get a p0170 series if the fuel pressure regulator faulty. and lastly , have the evap purge valve tested; it may leak false (gas vapor) air into intake system and change the fuel mix. my guess: its the mass air flow sensor is out of range. if my guess is correct, the rotor adapation(rpm sensor) will need to be reset with an sds and the adaptation too. other methods are available to reset the ecm, as much has been written about this whole matter in these forums. anyway, i would install a german made air filter with it too which will help block sand particals which mess it up the maf sensor in the first place. buy quality parts for a quality car.
 

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1998 E320
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52 Posts
Discussion Starter #3
Thanks! I just replaced the filter last week with an OEM Mercedes filter. That made a huge difference with the CEL going off every second vs going off once every couple days.
 

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'01-E320 & 02-ST2
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If you do a SEARCH you will find that over 99% of the time, when you get those two codes together on a late-model benz (170 & 173) -- even when the car runs fine -- it is the MAF. Some get a few extra weeks of life by cleaning it, but end up replacing it anyway. Continue driving long enough with a failing MAF and you will end up damaging more costly components like O2 sensors and cats from too lean and too rich mixtures.

So get a genuine bosch replacement from a reputable source (not ebay, the inserts are cheap chinese knockoffs that will give you a new set of problems (which you'll see if you search) and you can get the whole thing from autohausaz.com for about 175 with free shipping.

Last, housekeeping, please click the user cp link and complete your profile to include vehicle and location information as that is useful most of the time and particularly when you're seeking advice. Here for example we don't even know what car you have and are assuming you picked the right forum, but in any event there are at least six different engines in the US and several more in other markets...which of course can make a difference. (Edit: I now see a 98 E320 in your sig, but please do put it in your profile and we don't have to search around looking for it.)

Take care and enjoy the ride,
Greg
 

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1998 E320
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52 Posts
Discussion Starter #5 (Edited)
Thanks Greg. I actually did do a lot of SEARCHING which is why I was posting the question on here. The problem I'm having right now is due to a SINGLE code (P0173) and not BOTH codes (P0170 & P0173). In my searching I did not find very much pertinent to that issue. Most of the things I found (99% of the time!) were related to the MAF sensor because BOTH codes were tripping.

That was my next route to take was to purchase a MAF, thanks for the info on autohausaz.com by the way, but I didn't want to spend the money on something that wasn't actually the problem if someone else here had experienced the same thing.
 

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1998 E320
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Discussion Starter #6 (Edited)
I'm curious if maybe I'm getting the P0173 due to a faulty O2 Sensor and maybe the air filter being fouled up caused the same kind of other problems. So my MAF might actually be OK and maybe it's just an O2 Sensor. Do you know any way to test them to see if they are within the operating specs?

I had a 1998 C230 that my wife totaled ... so we just picked this one up a few months ago and I'm trying to give it a little TLC and a better life from the last owner.
 

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Hey, calebfrida. My apologies, I was using a smartphone and missed that you had cleared one of the codes and it was staying off.

Even without a cel you can have pending codes so check them regularly. It's weird that you would have both but then only one. However, if all you have is a pending code (and no CEL) and the car is running fine, then you can safely ignore it.

Single fuel trim for one bank is often a vacuum leak, O2 sensor or partially-clogged cat. Running a dirty air filter for a while could exacerbate an issue and help melt a cat or overheat an O2 sensor, but start cheap, begin looking for a vacuum leak on that bank first. There are lots of vacuum lines and diaphram-devices and a couple of cheap plastic check valves that can crack and leak (including one on the EGR).

I didn't see mileage in your post, but O2 sensors are a 100K check/replace interval so if you're there or over change both the front ones for now, if DIY buy the universal bosch and splice them in, saves some dough. Use bosch's part finder, then search for the P/N at autohausaz. (They are really great for OEM stuff, good prices, fast shipping -free at $50, even for heavy stuff like rotors- and nice folks to deal with on the phone or in person.)

You can test the MAF if you like, I posted a spec sheet for it up in the stickies.

Hope no one was hurt in the loss of your 202, but you're really going to love the 210. :thumbsup:

Take care and enjoy the ride,
Greg
 

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1998 E320
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Discussion Starter #8
No Problem Greg! Thanks for all the info! You've been a great help!!

I don't know if this makes any difference or not but I pulled my MAF off last night and cleaned it up a little bit. The bar that the air passes through did have some dust on it ... about an 1/8 inch of it's width had some statically charged dust covering it. I'm not sure how much difference it will make, but I'll post back wither or not my CEL comes back on in a couple days.

I wish I had looked more closely at the freeze frame data the first couple times the CEL activated. It seems to be tripping only when I'm backing off the accelerator and slowing down to a stop. So I'm wondering if it's possible that if the MAF is partly "clogged" then the error would trip when there's not as much air passing through the intake. It's weird that I never seem to throw the CEL when I stomp on the gas or make a quick traffic manuever.

There were a couple scattered records that came with the car, so I'll check when I get home tonight and see if any o2 sensor's have been replaced. The car has 146,000 miles on it now and I got it with around 142,000. I loved the w202 and didn't think a car could get much better, but the W210 is proving me wrong! :D

My wife is from overseas and lived in the middle of a big city, so she's never had a need to drive. So we actually bought the 202 so she had a safe car to drive in case she was in a wreck ... so it served it's purpose. The car was pretty beat up but we walked away from it. Cars can be replaced! She did however take down two rather large cedar trees! :eek:
 

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No Problem Greg! Thanks for all the info! You've been a great help!!

I don't know if this makes any difference or not but I pulled my MAF off last night and cleaned it up a little bit. The bar that the air passes through did have some dust on it ... about an 1/8 inch of it's width had some statically charged dust covering it. I'm not sure how much difference it will make, but I'll post back wither or not my CEL comes back on in a couple days.

I wish I had looked more closely at the freeze frame data the first couple times the CEL activated. It seems to be tripping only when I'm backing off the accelerator and slowing down to a stop. So I'm wondering if it's possible that if the MAF is partly "clogged" then the error would trip when there's not as much air passing through the intake. It's weird that I never seem to throw the CEL when I stomp on the gas or make a quick traffic manuever.

There were a couple scattered records that came with the car, so I'll check when I get home tonight and see if any o2 sensor's have been replaced. The car has 146,000 miles on it now and I got it with around 142,000. I loved the w202 and didn't think a car could get much better, but the W210 is proving me wrong! :D

My wife is from overseas and lived in the middle of a big city, so she's never had a need to drive. So we actually bought the 202 so she had a safe car to drive in case she was in a wreck ... so it served it's purpose. The car was pretty beat up but we walked away from it. Cars can be replaced! She did however take down two rather large cedar trees! :eek:
Benz products do seem to withstand the vigors of accidents and sacrifice themselves for the occupants quite well, glad you weren't hurt.

I doubt that cleaning will have an effect on your code. Any issues with the main intake (including the MAF cleanliness) will trigger codes on both banks, not just one.

However, your attention to detail is admirable and the fact that it triggers on deceleration makes me think that it is most likely a vacuum leak, because that is when vacuum is highest, so I'd look at that stuff pretty hard. One of the 208 drivers with the 112 engine posted quite recently about a leak at the intake manifold gasket, too, so another place to check.

Take care and enjoy the ride,
Greg
 

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1998 E320
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Discussion Starter #11 (Edited)
I'm keeping my fingers crossed but so far I haven't thrown any codes since cleaning the MAF. I'm going to dig around this weekend and see if I can find any vacuum leaks just in case.

Thanks for the help guys! :thumbsup: I'll keep this posted if I find anything else.
 

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1998 E320
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Discussion Starter #12
So far I haven't thrown any more CEL codes *Fingers crossed*. I do have another question though. When I'm idling at a stop light my Tachometer seems to sit around 600-650. When I pull up to a stop light (slowing down), as I complete a stop, it seems that the Tach drops down to about 550 - 600 once then sits aroudn 600-650. It's not much but I'm curious if that means vacuum problems or if that's just normal?

My C230 did the exact same thing so I don't know if that's just the Mercedes or if by fluke that car had the same issue.
 

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1998 E320
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Discussion Starter #13
Well it's gone about a month and a half with no codes and now the codes are back! The CEL is tripping about once a day, usually driving very slow and coming to a stop. I can stomp on the gas and never get a code.

It's a mix of codes. One time it will just be the P0173, and the next time it will be P0170 & P0173. It's back and forth. I'm going to stop by my independant shop this week and get the oil changed and see if they can hook up the uber computer too it and see what's up.
 

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since cleaning of the maf took away the error code for a while, but now same code reappeared should tell that maf is the problem.
 

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2000 Mercedes E320
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I had the same codes and tried cleaning. As Greg said, maybe you get another few weeks or so. My codes eventually came back and I then added a can of sea foam to the gas tank, and drove a day or two then ended up replacing MAF insert only. (Germanstar $130) The ride has been running really great ever since. Good luck!

Brent
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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The symptom of "feeling like it is just about to stall" is a symptom of the failing MAF.

From your description yours was real "dirty", and congrats on the cleaning, but you are best served getting a replacement MAF. If you don't disconnect the battery for the install (most don't, note the CEL may take several cycles to clear) I would recommend you also do a 3 minute do a "soft reset" to perk your car back up to the default settings, default settings combined with a new MAF zoom-zoom.

Thnink about a DIY plug change to using new OE Bosch plugs, depnding on your budget and intention.

Keep the beat !
 

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1998 E320
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Discussion Starter #17
I stopped by the local shop this week and had my oil changed. While they were doing that I had a freind that works there hook the benz up to the computer. The MAS was measuring a 12 at idle and he said it should be between 12 and 24. When the engine was revved it would lag a second and then slowly jump up to somewhere between 50 to 80. On the way back down my MAF would drop to an 8 and then bounce back up to a 12. That would explain my slight stutter when I was stopping and also why the CEL was popping up when it did.

We swapped my MAF out with a tester unit they had on the bench and now the MAF was reading a steady 16 at idle. When the engine was revved it would immediately bounce up to 120-130 and then go straight back to 16.

Needless to say I just ordered a new MAF from AutoHausAZ.com that should come in tomorrow or wednesday. Is there anything special I need to do to the computer when I install it or will it self correct after a few trips?

Sorry in advance for any weird spelling or grammer. It's been a hell of a monday already...

Thanks for the help guys!
 

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With new MAF, the CEL will clear after about 7 restarts.
Took me about 10 seconds to do that.
Whole MAF replacement and CEL resetting is about 3 minutes job.
No wonder stealers charge only $300 for it. ;)
 
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