MAF fault

[Richard65]

Engine management light has come on and I asked my independent to read it when I collected our Polo from service. They said its a MAF error code which they cleared and that lasted for a couple of days but has now returned so clearly needs sorting out. I've check price and it's over £700 from MB or £417 as an exchange part so either way an expensive failure with fitting. Should I invest in the iCarsoft Professional Multi-System Auto Diagnostic Tool MB V2.0 so that I can read all the codes myself and make sure that I have a better idea of the problem. Or is there another tool that is more suitable?

Thanks

 

[LostKiwi]

What did they use to read the codes?

If it was a generic OBD2 reader it may not report correctly.

I think a code reader capable of reading MB codes is a must for owning a Mercedes.
If you have an Android phone the Autel AP200 is a decent bit of kit to keep in the glovebox.

Not perfect (the graphing capabilities are a bit flaky) but certainly good enough to read and clear error codes.

 

[Richard65]

Thank you - I've got the AP200 and done a scan and found a few things I can sort out (batteries in tyre pressure sensors etc.) and most codes I've cleared and are not current but there is a code P010C38 which is noted as
'Motor Electronics (ME) 'SIM271DE20" for combustion engine 'M271EVO'
I presume this is the MAF sensor and the car will be in for a check on Tuesday and I'm assuming this will be a replacement MAF sensor unit but I'm more interested to know what the fault is and also if there is any online error code reference for MB vehicles

 

[LostKiwi]

Generally I use Mercedes source to find more info on codes but he doesn't have them all and in this case it doesn't appear to be there.
Mercedes often use subcodes as in this instance.
The main code is P101C and subcode 38 (sometimes shown as P101C-38).

On some readers the subcode will give more detail about the fault (failed, implausible values, too high, too low etc).

Star diagnosis will give more details.

 

[mattkh]

The main code is P101C

You mean P010C.
I reckon the MAF filament is getting fouled up by engine oil. Do we know the mileage..?

 

[supernoodle]

P010C is one of the codes specified in ISO15031-6, so it should be same regardless of vehicle, as long as it post dates this spec (2005).
Your car is much later so it should hold true.

P010C is
Mass or Volume Air Flow “B” Circuit Low

Failure byte 38 is Signal frequency incorrect.

The code implies the signal is missing or there is a short.

If it was sensor was contaminated you'd expect a P010B Mass or Volume Air Flow “B” Circuit Range/Performance, but it depends how they've calibrated it.

There should be freeze frame data stored when the fault was triggered, Merc might have kind enough to put the individual bank airflow readings in.

When the code triggers would be telling too, at key on or after some specific manoeuvre?

 

[Richard65]

Thanks again for the response. I'd found this breakdown of the code from an MB Sprinter link online so I guess it's similar, but not specific. What I was trying to find was more information about the MAF unit as it's available as an exchange and the main body is just a plastic moulding with gaskets to connect but inside I think there are two sensors so was interested to know if it was just one sensor failure

P010C is one of the codes specified in ISO15031-6, so it should be same regardless of vehicle, as long as it post dates this spec (2005).
Your car is much later so it should hold true.

P010C is
Mass or Volume Air Flow “B” Circuit Low

Failure byte 38 is Signal frequency incorrect.

The code implies the signal is missing or there is a short.

If it was sensor was contaminated you'd expect a P010B Mass or Volume Air Flow “B” Circuit Range/Performance, but it depends how they've calibrated it.

There should be freeze frame data stored when the fault was triggered, Merc might have kind enough to put the individual bank airflow readings in.

When the code triggers would be telling too, at key on or after some specific manoeuvre?

Thanks for this. My independent can read the codes but I don't know if they have full Star diagnostic tools, I assume so. When I read the car with the Autel AP200 I got a whole load of codes, most of which I have cleared and have not reappeared, lots related to the destruction of the wing mirror but there are codes for a faulty speaker, antenna, parking, camera etc which generally not important. The other codes which give no more detailed information are U103888 - Communication with the diagnostic CAN bus is faulty. Bus OFF and U103812 - Communication with the daignostic CAN bus is faulty. There is a short circuit to battery(+).
The main code P010C38 - 'Motor Electronics (ME) 'SIM271DE20" for combustion engine 'M271EVO' I've assumed is the MAF sensor and your comment about the contamination is significant as I thought these engines also had a turbo gasket issue. I'm happy to leave it to the garage but if there is an underlying cause I'd rather find out. If I have to replace the MAF sensor every 68k miles (current mileage) so be it. It's expensive but these machines are complex. If there is an underlying fault causing the MAF sensor error which is already known it would be good to know. My garage cleared the code and I drove for 2 or 3 days without the warning light reappearing and then starting the car one evening the engine management warning light came on again. Nothing more specific than that. But it tends to imply that the sensor may still be working and that it is picking up some fault with air flow. The Autel AP200 will not let me clear this code although I can clear pretty much everything else.

 

[supernoodle]

Well the Autel is plugged into the diagnostic CAN, so hopefully it wasn't that that caused the CAN faults. It's obviously working, though. Monitor to see if they come back.

There is an equivalent P0102 code for the MAF "A", so code is only pointing to one of the sensors.

When you say the fault doesn't clear, do you mean the tool gives a negative response to the request to clear or the tool gives a positive response but when you read the codes the fault is still there? If it's the latter that's consistent with it being a missing signal or short. Electrical diagnostics flag instantly, plausability diagnostics only run when conditions are correct. It would mean fault is still present.

Faced with prospect of forking out £400, I'd make sure it gets diagnosed properly first. Given the car has two there's a good one to compare against. They could even swap them. If the tech is handy with an oscilloscope they can check the signals, they are variable frequency.

 

[LostKiwi]

You mean P010C.
I reckon the MAF filament is getting fouled up by engine oil. Do we know the mileage..?

The breathers are downstream of the MAFs. Unlikely they're fouling with oil.

 

[Richard65]

Just run another scan and the AP200 does not recognise the module even though it generates a fault code. I have emailed a report to them to ask if they have a firmware update. Meanwhile I have managed to clear the fault code. I don't detect any difference driving or performance and so will try and see what circumstance causes the management light to come back on before forking out for a replacement sensor. Thanks to all for the advice and help.