P0101 Fault - Help!!

[Timotheus]

Hi,

I have a C250 CDI Sport and on Sunday the engine management light appeared and the car went into limp mode. I managed to get it diagnosed on Tuesday and yesterday I fitted a new MAF sensor and air filter, believing this could resolve the issue. I then got a friend to reset the ECU but the car remains in limp mode and the engine management light quickly reappeared. One of the reasons I suspected the MAF sensor was because I have been suffering very poor fuel economy, typically getting less than 400 miles on a tank of diesel. I'm now wondering what other cause there might be. I am advised that it would be worthwhile checking the EGR valve and cleaning it and also that the MAP Sensor could be faulty. Can anyone offer any advice?

 

[Trickythemerc]

What codes did you get for the original diagnosis ?

 

[SteveK9]

Does disconnecting the MAF make it perform differently? The chances are if you can get a code reader and you are getting a code relating to the MAF there is a leak or restriction somewhere in the air supply making it give implausible readings and causing the limp mode. A decent reader will point you in the right direction and if you can look at live data you should be able to see if the EGR is functioning as well as what's going on with the MAF and other sensors that are used in conjunction with it to provide the right mixture.

 

[Mercedes man]

Hi check inlet manifold manifold done a few now and bolt shears and blows plastic away

 

[jon.english68]

I have a 2012 C220 CDi with the same issue, P010129 Mass Airflow Sensor 1 has a fault, there is an invalid signal. I have read everything on the web I can find on this code and it seems it is anything from a faulty air filter to an air leak to a cracked inlet manifold or a blocked exhaust, so I have stripped down the engine to check the inlet manifold, checked for air leaks, checked the EGR valve and cleaned out the DPF, non of the above had a visible issue with the exception of the air filter body is cracked where is slots over the MAF sensor, I have replaced the boost pressure sensor due to its location and the air filter and re-assembled the engine with new seals and I still cant delete the code but live data I can see the MAF sensor showing air intake but as I dont know what the data should be I dont know if it is correct or not, been off the road now for 2 months.

 

[SteveK9]

I have a 2012 C220 CDi with the same issue, P010129 Mass Airflow Sensor 1 has a fault, there is an invalid signal. I have read everything on the web I can find on this code and it seems it is anything from a faulty air filter to an air leak to a cracked inlet manifold or a blocked exhaust, so I have stripped down the engine to check the inlet manifold, checked for air leaks, checked the EGR valve and cleaned out the DPF, non of the above had a visible issue with the exception of the air filter body is cracked where is slots over the MAF sensor, I have replaced the boost pressure sensor due to its location and the air filter and re-assembled the engine with new seals and I still cant delete the code but live data I can see the MAF sensor showing air intake but as I dont know what the data should be I dont know if it is correct or not, been off the road now for 2 months.

I had the same fault as you on a 1012 E250CDI and looking at live data led me to the MAP sensor, I ordered and fitted a new Bosch one which I got from the local factors but it didn't fix the issue and after checking everything else I gave up and sent it to the local MB specialists. They eventually found the MAP sensor I had been supplied was the wrong one, replacing it with the right one immediately fixed the issue. Moral is always to check the supplied part is the right one. What reader are you using as there should surely only be one MAF sensor?

 

[jon.english68]

I had the same fault as you on a 1012 E250CDI and looking at live data led me to the MAP sensor, I ordered and fitted a new Bosch one which I got from the local factors but it didn't fix the issue and after checking everything else I gave up and sent it to the local MB specialists. They eventually found the MAP sensor I had been supplied was the wrong one, replacing it with the right one immediately fixed the issue. Moral is always to check the supplied part is the right one. What reader are you using as there should surely only be one MAF sensor?

thanks for this info Steve, Im reading it with my Launch X431, the only code I have is P010129, Im going to get the code read on Monday with Autologic so hopefully I will know more then.

 

[SteveK9]

I use a Maxidas 906 which gave me a MAF fault and talked about an intermittent signal but as I say this was a complete red herring, there was no mention of a MAP error it was only live data that pointed it me to that. Not knowing what I should have been getting but seeing a widely varying signal, dropping to nothing occasionally seemed to indicate it was a MAP issue so for the sake of a few pounds and grazed knuckles it seemed worth a punt. The signal from the new (wrong) sensor looked coherent so I thought I'd fixed it but couldn't clear the code and it still dropped into limp mode. Following that and trying a known good MAF from another car and checking for boost pipe leaks etc. sent me to the specialist and you know the rest of the story. BTW it would seem running on limp can rapidly block the DPF and it won't regenerate which can compound the issue so I would recommend forcing a regen once you do get it sorted.

 

[DSM10000]

Get a Star diagnostic by someone experienced in using it.

 

[jon.english68]

Get a Star diagnostic by someone experienced in using it.

very helpful, thank you