W639 Vito MAF fault P0101 / P010106

[Shumart]

I've got a 2012 W639 Vito 113 on approx 200k, which earlier this week decided to go into limp mode.
I've checked the codes with my Icarsoft MB2.0 and got the following codes:

P0101 Mass or Volume air flow sensor A circuit range / performance
P010106 Mass air flow sensor 1 has a malfunction. There is an algorithm fault.

P0101 resets and goes away until the engine is stared.
P010106 does not reset even with the engine off

MAF shows approx 14g/s on idle and is steady, responds when I blip the throttle
MAP looks ok at 1.02Bar
Boost responds, 1.02 bar when engine off, responds when throttle blipped with engine running
Intake temp looks reasonable.
DPF 88% full

Tried cleaning the MAF but made no difference. wiring looked ok, only checked uo to it goes into the plastic trunking on the head.
Loom checked up to the SAM and nothing has rubbed through the loom tape.
Re-seated the ECU plugs
Pipe from the air filter to the turbo intake looks ok as does what I think is the crankcase vent which tees into it.
Recently done the plastic engine coolant manifold, which required the EGR cooler to be removed. That was reasonably clear.

I'm thinking more air leak than MAF fault, I need to get underneath and check the intercooler pipes the weekend.
anything else I should be looking at?

Thanks in advance

 

[Shumart]

Checked the two intercooler hoses, the turbo side had a internal seal that looks a bit flat but no holes. Stuck some ptfe tape round it to pad it out until I get a new pipe. Inlet manifold pipe and seals look ok.
Can't get the code to clear even with the engine off, any ideas?

 

[SteveFromAvantgarde]

Occasionally get faults with the actual MAP and pressure sensors and they have been modified.....could be that.

The algorithm must be equal across all 3 sensors, if not it will kick up a code. The fact it wont clear and comes straight back says its more sensor related. If it was an air leak, the fault would clear and only come back when its on a boost measurement and it sees the air deviate from the spec value.

 

[Shumart]

I'll take another look at the sensor values.

I rigged up a compressor to the intake hose and pressurized it to 0.5 bar and couldn't hear any leaks. Tool about 5 seconds for the pressure to drop to zero but my improvised blanks were leaking a little. I presume a leak large enough to cause this would be quite large and audible

 

[Shumart]

So I've have had a look at the sensor values, nothing seems out of the ordinary to me except 1...
Boost pressure downstream of low-pressure turbocharger 0.06 Bar
Is this a sensor that is used? If so I would expect it to read 1 bar like the rest with the engine off.

All values with engine off after running for a couple minutes on a cold day

Air mass per stroke 520 (at idle) always defaults to 636.02 with engine off
Air flow rate from Mass air flow sensor 0.06g/s with engine off, 15g/s at idle, responds when engine revs

Air intake temp 6 degrees
Ambient air temp 2 degrees
Boot air temp 5 degrees

Boost pressure 1.02bar
Exhaust back pressure 1.03 bar
Intake manifold pressure 1.02 bar

 

[Shumart]

From what I can see on other Mercedes diesels the Boost pressure downstream of low-pressure turbocharger reading is indeed around 1 bar normally.
I cannot find this sensor tho, anybody know where it is?

 

[Shumart]

So I bit the bullet and took it to a garage, in case somebody else has a similar problem I'll post the results.

So the garage "Performed recalibration of the air flow sensor & drift calculations" EML went out, they took it for a blast down the motorway. DPF re-genned and all is good.

The likely cause was a boost leak from the hose I changed originally, but unless you recalibrate the system after the fault has been fixed the fault wont clear.
Boost pressure downstream of low-pressure turbocharger reading low was a red herring, still is low now and no faults. I presume this sensor is not fitted on my engine.

Readings now are a little lower then before but ambient air temperature is much higher at 14 degrees (was 2 degrees before) so this is to be expected I think
MAF shows approx 12g/s on idle
Air mass per stroke 480

So if this happens to anybody in the future, if your sensor values look ok check the two rubber charge hoses to the intercooler, particularly the "V" section o rings (not sure if that is the correct name but that's what they look like) the should be in good condition and stick firmly proud of the metal fitting when installed.
Charge hoses are easy to remove, just a spring clip each end which can be unclipped with a flat blade screwdriver. Will take a couple minutes per side with the van on ramps.
The V section o rings seem to be available individually on eBay for £10 each.
I bought a whole new hose (drivers side) from Mercedes, this was about £120 inc VAT
Local garage charged 1.5hrs labour to to the recalibration / adaptation of the MAF and take it for a drive.

 

[Shumart]

So its been 3 months and the fault has come back so I thought I would update the thread with what happened and what finally (hopefully) has fixed it.

So much like before the van went into limp mode whilst decelerating from approx 20mph, same codes as before. Algorithm fault wont reset with engine on or off, MAF unplugged or not. Sensor values look reasonable like before.
So this time I took it straight to the garage. Explained the problem and when it happened and they thought it sounds like a air/boost leak.
They smoke tested it and found nothing, pressurised the intake side up with compressed air and found nothing. Changed the MAF and the codes reset before they even plugged their computer in.

The values I get now are:

MAF shows approx 16g/s on idle
MAF shows approx 0.18g/s with engine off
Intake temp 11 degrees and the engine is cold.

Not too far from what I had before.

So if you are sure you don't have a boost leak and your algorithm fault will not reset, try changing the MAF. Genuine Mercedes one was approx £220 so check the rubber engine to intercooler hoses and seals first!