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M112 MAF Sensor Replace/Cleaning
Thread Starter
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Joined: Aug 2008
Posts: 273
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From: SE PA
2001 C320
M112 MAF Sensor Replace/Cleaning
Okay, since there is no MAF sensor replacement procedure in the DIY thread for the 3.2 liter, I figured I would post a write up since I recently pulled mine out to clean. The dealership just recently had my car and told me that I would need a NEW Mass Air Flow sensor and that it was causing the CEL to trip. Knowing their reputation of simply replacing parts, I opted for them to do nothing. After I got the car home, and had a free weekend, I proceeded to remove the MAF and throttle body for a thorough cleaning. After this cleaning (which has been about two weeks now), there hasn't been a CEL on. First thing I did was picked up some cleaners for the job. I went with CRC, I've used this brand before and they are always a quality product. Just over $12 for the MAF Sensor cleaner and the Throttle Body cleaner. A couple other tools you'll want for the job, I used a 3/8" ratchet along with a T-40 Torx for the throttle body bolts. I also used a big flat head screw driver for removing PCV hoses and removing the plastic ring/clip that holds the MAF sensor in place. Your very first step is going to be removing the air cleaner assembly.
Last edited by PA_Pete; Nov 9, 2008 at 12:38 PM.
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Step Two
Okay, next step was to unhook the plug from the MAF sensor on the right side of the assembly looking at it from the front of the car. It comes right off when you depress the two tabs on opposite sides of one another. Next was too take off the plastic retaining ring, now I'm not sure what the correct term for this piece is, but it wraps around the MAF assembly and clips together in the middle. It's used to hold the assembly in place so that it won't move around on the throttle body. After unhooking this ring (I'm doing this write up from memory), you should be able to lift the MAF sensor straight up from the plastic elbow that connects it to the throttle body. Here are some pictures of the MAF sensor off of the car. I sprayed the cleaner straight at the hot wire (the wire within the plastic piece in the middle of the MAF sensor) without touching the wire itself. I sprayed it thoroughly than set it to the side to dry off completely.
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Step Three
Okay, after setting the MAF sensor aside to dry, I moved on to removing the plastic elbow the joins the MAF sensor to the throttle body. There is a PCV hose that connects to the right side of this elbow and routes underneath the fuel rail and injector wiring. I removed this hose from both the elbow and the valve cover. After that is out of the way, you can see two clips, the top one is on the right of the elbow while the bottom one is on the left portion of the elbow, these hold it against the throttle body. Depress the clips while pushing the elbow towards the firewall to remove. It's tight in there, so be patient and try to twist the elbow to the right while pulling up at the same time, it took a little fooling around with it before it slid out off of the throttle body. Sorry, but I do not have any pictures of this step, it's a handful.
Last edited by PA_Pete; Nov 9, 2008 at 12:49 PM.
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Step Four
Okay, now that the plastic elbow is out of the way, you can worry about removing the throttle body. Note, removal of the throttle body or even the elbow is not necessary if you are only cleaning or replacing the MAF sensor. Okay, there is a rubber junction that plugs into the top of the throttle body. This is where two PCV hoses plug into for blow-by and another plastic tube (not sure what this is for, may regulate idle speed or intake vacuum), be careful not the break or crack the plastic tube, it feels very fragile! You can pull the plastic tube straight up to remove it from this junction piece, once you do that, try to move it off to the side without breaking it, next you only really have to remove one of the PCV hoses off of the junction piece, I did the left side (passenger). After this, you can pull up on this junction piece to remove it from the top of the throttle body. On the bottom right (driver's side) of the throttle body is the plug which controls the butterfly, unplug this. Now you can bust out that T-40 Torx and loosen up the four bolts that hold in the Throttle body. NOTE, you may unplug the throttle body connection after removing the throttle body from the intake plenum. I did this and there was enough wire to do it. Now, you should have the throttle body off of the intake.
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Step Five
Okay, now that your throttle body is out, you can clean it. Mine was filthy, the pictures I have of it in the previous thread were after I cleaned it. You may also want to look into you intake to be sure you didn't get anything in there, I used a mirror and a flashlight. Also, check the gasket/o-ring that sits in the intake, I did not remove this since I didn't have a replacement, but I did look it over to make sure it wasn't cracked or ripped. Sorry, but these are the best pictures I have of the throttle body removed from the intake.
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Step Six
Okay, now that everything has been cleaned, you can start to re-assemble everything in the reverse order in which you took it apart. I'm not positive on the torque rating for the throttle body bolts, but I do know that they weren't on there insanely tight, so I put them pack on with about the same pressure it took to take them off. If you feel uncomfortable doing this, find out the torque rating for these bolts and use a torque wrench. After re-attaching the throttle body and PCV connections on top of the throttle body, I assembled the plastic elbow piece to the MAF sensor as one piece to put back onto the throttle body. NOTE, there are big rubber o-rings that fit on both ends of the elbow, be sure these are back in place when piecing back together. That's about all I can say for this DIY. I'm assuming that the procedure is the same for the 2.6 liter in the C240, so you C240 owner's may be able to use this also, if I wrong, someone please let me know. Also, if anyone else has done this job and has anything to add, especially pictures, please do so, I hope this comes in useful for someone!
Last edited by PA_Pete; Nov 9, 2008 at 12:45 PM.
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Joined: Apr 2006
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From: Seattle
w203 m112
Great write up 
Nice job pete.
I have taken my MAF elbow and MAF off the car before and agree that it is extraordinarily unclean due to the crank case breather hoses that connect to this part. Adding a catch can has been on my to do list for some time now... If anyone is interested in this process, Brandon (code3performance) has done one on a m112k (c32/slk32) engine and has a DIY posted. Search!
Nice job pete.I have taken my MAF elbow and MAF off the car before and agree that it is extraordinarily unclean due to the crank case breather hoses that connect to this part. Adding a catch can has been on my to do list for some time now... If anyone is interested in this process, Brandon (code3performance) has done one on a m112k (c32/slk32) engine and has a DIY posted. Search!
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Joined: Jul 2006
Posts: 3,365
Likes: 12
From: Orange County, CA
GMC - Miata - Trek - P-Car
Excellent DIY, PA Pete. Appreciate you sharing the procedure.
It’ll be rather nice if you’ve avoided an unnecessary MAF replacement by investing some time and inexpensive consumables instead.
Surprising amount of blowby in these engines.
images credit HDDP
It’ll be rather nice if you’ve avoided an unnecessary MAF replacement by investing some time and inexpensive consumables instead.
Surprising amount of blowby in these engines.
images credit HDDP
Last edited by splinter; Oct 6, 2010 at 07:02 AM.
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Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Great write up Nice job pete.
I have taken my MAF elbow and MAF off the car before and agree that it is extraordinarily unclean due to the crank case breather hoses that connect to this part. Adding a catch can has been on my to do list for some time now... If anyone is interested in this process, Brandon (code3performance) has done one on a m112k (c32/slk32) engine and has a DIY posted. Search!
Nice job pete.I have taken my MAF elbow and MAF off the car before and agree that it is extraordinarily unclean due to the crank case breather hoses that connect to this part. Adding a catch can has been on my to do list for some time now... If anyone is interested in this process, Brandon (code3performance) has done one on a m112k (c32/slk32) engine and has a DIY posted. Search!
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
What's that supposed to mean?http://www.crcindustries.com/auto/
You should be able to get it at an Advanced Auto or other autoparts store, that's where I got mine at.
http://www.advanceautoparts.com/
I did this write up for the M112 engine, which is the 3.2 V6. Your car would have the M111 2.3 liter inline 4. I believe there is already a write up on how to do your MAF in the sticky's.
EDIT: Sorry, the DIY thread in the sticky's is actually for the M271 (1.8L) engine.
https://mbworld.org/forums/c-class-w...placement.html
Last edited by PA_Pete; Feb 17, 2009 at 03:31 PM.
Member
Joined: Jan 2008
Posts: 87
Likes: 1
From: Gainesville, FL
Black 02' C230
What's that supposed to mean?The cleaner I used was CRC Industries, I've always loved their products.
http://www.crcindustries.com/auto/
You should be able to get it at an Advanced Auto or other autoparts store, that's where I got mine at.
http://www.advanceautoparts.com/
I did this write up for the M112 engine, which is the 3.2 V6. Your car would have the M111 2.3 liter inline 4. I believe there is already a write up on how to do your MAF in the sticky's.
EDIT: Sorry, the DIY thread in the sticky's is actually for the M271 (1.8L) engine.
https://mbworld.org/forums/c-class-w...placement.html
Thread Starter
Senior Member
Joined: Aug 2008
Posts: 273
Likes: 6
From: SE PA
2001 C320
Thanks Glyn, and as you know, I always take plenty back from your threads and posts!
DIY - Do It Yourself, that's the good one, DWI and DUI are the bad ones. You MIGHT be able to do yours based off of the M271 write up, but to be honest, I'm not too familiar with the S/C 4cyl. so, I don't know how they differ in engine setup and configurations. If you do yank your MAF for replacing or cleaning, why not take pictures and write something up, it can always come in handy for someone who hasn't been into their engine compartment yet. Oh, and then maybe (if it hasn't been posted already), make a thread about it.
DIY - Do It Yourself, that's the good one, DWI and DUI are the bad ones. You MIGHT be able to do yours based off of the M271 write up, but to be honest, I'm not too familiar with the S/C 4cyl. so, I don't know how they differ in engine setup and configurations. If you do yank your MAF for replacing or cleaning, why not take pictures and write something up, it can always come in handy for someone who hasn't been into their engine compartment yet. Oh, and then maybe (if it hasn't been posted already), make a thread about it.
Newbie
Joined: May 2009
Posts: 1
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From: Seattle, WA
2002 C320
I was having the most difficult time trying to take off the wire harness. I pushed on the two tabs so hard that my fingers hurt but the wire harness still wouldn't come off. The bottom tab was especially difficult since I couldn't really see it and it's harder to get to. Are there any tips and tricks that anyone can share with me? Thanks in advance!
Junior Member
Joined: Apr 2009
Posts: 43
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2004 C240
Thank you but I have a question...
Okay,
Got it all apart in very little time with that explanation. Thanks. Now, I noticed that I had some oil rummaging around the throttle body.
IS THAT NORMAL?
I was told or read somewhere that if oil gets on the MAF sensor, it'll keep it from running well and that the CEL will rear its ugly head. Mine has. MB can't fix it. They keep telling me it's the MAF sensor. I've put in 2 brand new Boschs now. It works for a week, then BAM! On with the CEL. I think it's because the oil is somehow getting thru but looking at some other pictures, there is oil on those too. I'll do some more research but it seems to me that's the problem and if it is, just where is the oil coming from?
Thanks!
Got it all apart in very little time with that explanation. Thanks. Now, I noticed that I had some oil rummaging around the throttle body.
IS THAT NORMAL?
I was told or read somewhere that if oil gets on the MAF sensor, it'll keep it from running well and that the CEL will rear its ugly head. Mine has. MB can't fix it. They keep telling me it's the MAF sensor. I've put in 2 brand new Boschs now. It works for a week, then BAM! On with the CEL. I think it's because the oil is somehow getting thru but looking at some other pictures, there is oil on those too. I'll do some more research but it seems to me that's the problem and if it is, just where is the oil coming from?
Thanks!
Super Member
Joined: Feb 2003
Posts: 523
Likes: 1
From: Hollywood North
CLK 55 ///AMG Cabrio, ML63 ///AMG
Removed the MAF sensor for the 1st time yesterday and I had the same issue. What I did was use a flat head screwdriver to help nudge the connector apart while depressing the 2 tabs. It can off fairly easily once the screwdriver was used, just be careful not to push the driver too hard.
I was having the most difficult time trying to take off the wire harness. I pushed on the two tabs so hard that my fingers hurt but the wire harness still wouldn't come off. The bottom tab was especially difficult since I couldn't really see it and it's harder to get to. Are there any tips and tricks that anyone can share with me? Thanks in advance!
Junior Member
Joined: Apr 2009
Posts: 43
Likes: 0
2004 C240
New Guy.... are you having the same problem?
Let me know, perhaps we can help each other out some? I'm at the point now where I believe it's a vacuum leak somewhere. Everything else is fine. It has to be. I've replaced the MAF 2x now. The only other thing that I could think of is that although the MAF says "BOSCH" on it, was it an aftermarket part that someone stamped "BOSCH" on? If so, that's real low!
Let me know...
Let me know...
Junior Member
Joined: Apr 2009
Posts: 43
Likes: 0
2004 C240
Can someone answer me this....?
The thick, black tube going into the "L SHAPED" tube (the one between the MAF and throttle body)... can anyone tell me what this tube is? What it stems from? There is oil in that tube. Perhaps that is why my "CEL" is on?
Thanks...
Thanks...
Junior Member
Joined: Apr 2009
Posts: 43
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2004 C240
okay... here's the scoop...
I've torn apart the MAF a few times, replaced with BOSCH, and still the "CEL" is on. This time though, only the "PO172 and PO175" codes come on. Thats "bank 2 too rich". So, based on that, what other things can anyone think of? Dirty fuel injectors? Bad oxygen sensors? HELP!!! I'm going MaD!
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From: Llandudno, Cape Town, South Africa
late 2009 CLK 350 Coupe Elegance, '65 Jaguar S Type wires
No - that's banks 1 & 2 too rich - what mileage has the car done? Is the air filtration in good condition? not clogged?
Last edited by Glyn M Ruck; Jul 21, 2009 at 07:04 PM.
Junior Member
Joined: Apr 2009
Posts: 43
Likes: 0
2004 C240
Thank u for the reply.
Pete, I've narrowed it down to the PCV system. Simple and makes sense. There was a time, last year, that I drove the car from Los Angeles to South Florida, where I am now and failed to change the oil after arriving. The oil got sludgy and nasty, but I did do the change eventually. I heard that sometimes the PCV will get dirty due to infrequent oil changes. So, I`ve gotten everything back apart and am now trying to remove the PCV fresh inlet hose from the `L tube` (you know, the L shaped tube between the throttle body and MAF?) Anyway, once I get that whole area taken apart, I'll know more. It makes sense for that to be the problem because I've taken apart and put back the MAF many times and sometimes the CEL goes off for a few days, perhaps because I cleaned some of the oil off. There is also oil in the throttle body. Not good. People say its okay but it seems to be a problem. I'll keep you posted because you may have the same problem.
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Joined: Apr 2009
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2004 C240
I think it's the PCV...
Miles? 70k. The air filter is fairly clean, I blow it out with the compressor every few months. Doesn't need a new one yet anyway. I think now that it is the PCV....
