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Discussion Starter · #1 · (Edited)
Hi,

Firstly I hope this thread is in the right section!

Some of you may have seen a thread I made recently (http://www.slkworld.com/slk-r171-ge...-cheap-diagnostic-scan-tools.html#post2746737) about diagnostic scanners, which one to get, as unfortunately my CEL came on recently.

Anyway, tonight I saw a friend who has a Snap On one, and these are the 3 codes that came up;

P0101 Mass or Volume Air Flow Sensor “A” Circuit Range/Performance
P0172 System Too Rich Bank 1
P0136 O2 Sensor Circuit Bank 1 Sensor 2
P0141 O2 Sensor Heater Circuit Bank 1 Sensor 2

My friend looked at the MAF flow rate on tick over (engine was warm) and it was at 2.58 g/s. Is this normal?

The O2S Voltage Bank 1 Sensor 1 was at 1.401V. Again, is this normal?

Please see the attached 3 pictures I took of his screen, it may have some more info that could help.


What are people thoughts on the fault codes I have/had? The car seems to be driving spot on by the way! Do you think I need a new MAF sensor? Can I clean my existing one with contact cleaner?

My first thoughts are it may be worth trying a new MAF or cleaning it, as I assume the 3 fault codes are linked, and maybe a dodgy MAF that is over reading is causing the car to over fuel and thus the bank 1 sensor 2 lambda probe is being screwed up. I don’t know, I am guessing! What are your thoughts?

Also which lambda probe is the bank 1 sensor 2? On my other car it has 2 lambdas, bank 1 (pre cat) and bank 2 (post cat). Does my 2008 SLK200 have 2 lambdas pre cat or something?

Finally, thought I’d mention, I noticed in the service history of the car which I bought only 15 days ago, that back in Sept 2014 it had a new “O2 down stream sensor”. Wonder if that’s the same lambda sensor in question?!

Thanks for reading, hopefully you can help.

James :)

EDIT: Just realised in my picture there is in fact a 5th code; its the first one which is highlighted in black, why it's black I don't know, maybe it's an old stored code, especially as it contradicts the system too rich code! Anyway... "P0171 System Too Lean 1"
 

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2019 SLC300
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Do not panic as it may have just been a one time thing. If he cleared them wait and see if they happen again. I have had this to happen. You said only had the car two weeks, could be a change in way of driving that the car needs to relearn.
 

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Discussion Starter · #3 · (Edited)
Yes my friend cleared the codes. I hope and pray you are right, but if so I would have expected the codes to say intermittent/sporadic etc. Time will tell. I just want to find out as much info as I can and have a plan of action on what to do to fix it assuming it will come back on soon! We have had the car for just over 2 weeks now and have done 330 miles in it. The engine management light came on after about 300 miles my dad said, so I guess it will soon come on again.
 

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Yes my friend cleared the codes. I hope and pray you are right, but if so I would have expected the codes to say intermittent/sporadic etc. Time will tell. I just want to find out as much info as I can and have a plan of action on what to do to fix it assuming it will come back on soon! We have had the car for just over 2 weeks now and have done 330 miles in it. The engine management light came on after about 240 miles my dad said, so I guess it will soon come on again.
Do you have any type of warranty or recourse back to the seller since you just bought it? If at all possible let this be someone else problem.
 

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Discussion Starter · #5 ·
Unfortunately not, private sale (sold as seen), so no come back. We love the car still lol, it drives great and this is only a minor problem that I will get around, hopefully sooner rather than later!
 

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Unfortunately not, private sale (sold as seen), so no come back. We love the car still lol, it drives great and this is only a minor problem that I will get around, hopefully sooner rather than later!
How many miles on the car? There are specific cleaners for the MAS. Worth a try if the code comes back. Other cleaners can damage the MAS. If any of our members that have the MB DAS system is close to you, it may be worth getting hooked up. That system will provide you with more info and ways to further trouble shoot the problem. As you suggested the codes may all be related.
 

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I had two of these codes (P171 and P136) when I used an ODB2 scanner and then a snap on scanner when I first bought my SLK200 a couple years ago. The engine management light had come on after a couple of weeks of ownership as in your case and I had no warranty.
The car seemed to perform normally, but I decided that I would be guessing from .thereon and I took it to an excellent indy in Norwich, UK (STR ).
He quickly diagnosed a split in a breather on the supercharger and charged me £180 for the whole job, which he said was a couple of hours work.
My view now, is that knowing the codes is a very small part of the problem.
Having a good indy mechanic (the local MB dealer seems good too) can save you a lot of time and stress.

Sent from my SM-T710 using Tapatalk
 

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I agree any thing can trip a fault code up etc

You need to make sure engine is running fine first as in plugs are ok air not clogged up oil fresh no hoses split or accidently come of or not connected properly .

Exhaust system has no leaks
Cat is good and fully working .

Then clear codes take for a long run and re check stored fault codes
And replace items .

Cheap O2 sensors can play up and throw up a code .
And cheap mass flow also .
Make sure all all elec connections are connected to .

And the snap on diagnostic scanner will be fine to use on your car if end user works it fine .
 

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Discussion Starter · #9 ·
How many miles on the car? There are specific cleaners for the MAS. Worth a try if the code comes back. Other cleaners can damage the MAS. If any of our members that have the MB DAS system is close to you, it may be worth getting hooked up. That system will provide you with more info and ways to further trouble shoot the problem. As you suggested the codes may all be related.
65,000 in total, but we have only done about 330 miles so far in it. The CEL came on after about 300 miles.

I had two of these codes (P171 and P136) when I used an ODB2 scanner and then a snap on scanner when I first bought my SLK200 a couple years ago. The engine management light had come on after a couple of weeks of ownership as in your case and I had no warranty.
The car seemed to perform normally, but I decided that I would be guessing from .thereon and I took it to an excellent indy in Norwich, UK (STR ).
He quickly diagnosed a split in a breather on the supercharger and charged me £180 for the whole job, which he said was a couple of hours work.
My view now, is that knowing the codes is a very small part of the problem.
Having a good indy mechanic (the local MB dealer seems good too) can save you a lot of time and stress
I will have a look at the pipe works, see if I can spot on splits. Where abouts are the breather pipes on the supercharger out of interest? can you point me in the right direction? lol thanks.

Also I will look for a good indy garage in my area (Essex if anyone can recommend) before I go out and buy anything, see what they say.

I agree any thing can trip a fault code up etc

You need to make sure engine is running fine first as in plugs are ok air not clogged up oil fresh no hoses split or accidently come of or not connected properly .

Exhaust system has no leaks
Cat is good and fully working .

Then clear codes take for a long run and re check stored fault codes
And replace items .

Cheap O2 sensors can play up and throw up a code .
And cheap mass flow also .
Make sure all all elec connections are connected to .

And the snap on diagnostic scanner will be fine to use on your car if end user works it fine .
Will try and have a look for split or popped off hoses etc. The car was serviced 6 months ago, had new plugs and filters etc, it seems to run fine so it is weird.
 

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Discussion Starter · #11 ·
I spent a good hour today looking for any splits in pipes/vacuum leaks etc but no joy. That said, I found 2 small areas where I could presence of oil, so there may a split breather pipe somewhere. I think I read the other day that there are breather pipes which often split under the inlet manifold, but that was on another Mercedes, but I assume mine will also have some pipes there too. I couldn’t see under the inlet manifold though unfortunately!

I have attached some pictures of the 2 areas I saw small amounts of oil present. One was on a plug behind the throttle body and the other looked like maybe some oil underneath behind the ECU, well I assume it’s the ECU?!

Can anyone please confirm if there are breather/vacuum pipes under the inlet manifold, and whether they often split? I assume there must be, I cant see how else the oil has got onto the plug behind the TB.
 

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