Headache

[Delta152]

Hi Guys,

Looking for some assistance (something I’m sure may be a common thread). I’m having map sensor issues and struggling to get to the bottom of the problem. The original fault occurred around a month ago when the EML light came on, car went into limp mode and flagged up with an air leak detected code(can’t remember the exact code). I cleared the code and sat stationery for around 20 minutes with the revs sitting at around 2500rpm. Doing this managed to do something (I’m unsure what) although the car was still struggling it got me to work and stayed out of limp mode.

I booked it into my local garage (not an MB specialist) and they said, the code was showing a leak because the pressure sensor just after the MAF sensor was showing as having a shortage. They changed the sensor and played around with changing the MAP sensor and the pressure sensor(although both sensors look the same I’m convinced they have different jobs but the garage said “no they both do the same job just further down the system).

The problem I now have is the car boosts okishhh until around 3k rpm when it start to judder and revs are all over the place. However it doesn’t flag a code and is leaving me stumped. I’m also unsure if the map sensor is in its correct location or if the pressure sensor is now in the manifold due to the garage messing around with them!

Any suggestions for the possible fault and part numbers for the pressure sensor(s) and map sensor would be obliged.

the car is a 2011 C250 OM651

thanks in advance.

 

[LostKiwi]

What are you using to read codes? Not every code reader will read all codes correctly (especially MB specific codes).

 

[Delta152]

What are you using to read codes? Not every code reader will read all codes correctly (especially MB specific codes).

It’s just a generic OBD2 code reader, nothing fancy. It’s my understanding that a star or a MB carsoft would be ideal, however giving severity of the fault I would like to think it would flag up a generic code. Having said that I’m fairly new to Merc so I could be wrong.

 

[LostKiwi]

I'm suspicious there are no codes.
Try looking at the live data for the MAP sensor (if you can) and see what it reports.

 

[Delta152]

I'm suspicious there are no codes.

Me also, my thinking is that the garage have somehow swapped the map sensor for the pressure sensor and although they do similar jobs, the jobs aren’t exact or the figures are just slightly out.
However if like you say there is a code or pending code that my OBD reader isn’t picking up on.
I’m reluctant to pay MB for a diagnostic for them to say we can’t find anything.

 

[LostKiwi]

Where are you based. We have a number of respected independent MB specialists we can recommend depending where you are.

 

[Delta152]

Where are you based. We have a number of respected independent MB specialists we can recommend depending where you are.

Motherwell, Scotland

 

[Delta152]

Hi, it’s not often you see follow up posts after a car have been successfully repaired so here goes. After taking the car to my local garage as previously stated they had fitted a new boost/Baro sensor (downstream of the air filter box but before the turbo).

I read somewhere that using non Mercedes parts could cause confusion, however the part that was fitted was Bosch and the same part number as what was on the old one.

I smoke tested all pipes and vacuum hoses all with negative results. I then removed the EGR valve to check for the common loose bolt at the underside of the inlet. Still nothing and the car was still running like crap. There was a plus to this though as I managed to clean a hole load of carbon deposits from the EGR and the inlet pipes.

I went on eBay and bought myself a MBII carsoft scanner which lone behold showed me some saved codes which wasn’t visible in a generic OBD scanner. The stored code was

P010628 “the intake manifold pressure sensor has a malfunction. The signal offset is outside the permissible range”.

P024114 “the boost pressure sensor for the low-pressure turbocharger has a short circuit to ground. There is a short circuit to ground or an open circuit.

After another couple of weeks of messing around checking wiring and re checking boost hoses etc. I was at my whits end with the car. I bought another brand new sensor from my local parts store (not MB) and still nothing.

This is when I remembered seeing a post about how sensors can act differently if they are not genuine MB parts, however I thought to myself, it’s a Bosch part.... Bosch make the part for MB then MB ad their catalog number with a new sticker.

I bit the bullet and ordered a second hand sensor from eBay for £6........

I fitted the £6 sensor and boom..... Full boost, car is no longer hanging onto gears and no more jerking when the auto box changes gear.

Since fitting the genuine sensor a few weeks ago the car hasn’t missed a beat.

A lesson to myself and anyone reading this, BUY GENUINE PARTS.

Bosh part number: 0 261 230 439
Mercedes part number: A 005 153 50 28

I have no idea why the Bosch sensor wasn’t working, I can only assume that my car’s software wasn’t up to date with the Bosch part, hence why the old second hand part worked perfectly.

I hope this helps someone out there.

 

[Mark A]

Glad you got it sorted & thanks for closing out the thread with your resolution.