Limp mode, 2800rpm max - going around in circles - Help!

[serow]

Hi all, well have I got a problem! Get your head around this if you can. My 2011, C350 CDI (204223)OM642 recently went into limp mode with a max rev of 2800rpm. Mileage is 68000 miles
It gave a code P0402 (14A700) excess flow...

I checked
EGR, found signal problem and replaced EGR. (MB)
Pressure sensor EGR gas A0071534328 replaced (MB)
Pressure sensor charge air A0061539928 replaced
Air intake temp sensor replaced - see comment below #
DPF pressure sensor A0061539528 replaced (MB)
DPF pressure pipes removed and checked - all clean and clear.
Manifolds and associated pipework recently removed (5000miles back) and cleaned of all carbon deposits
Swirl flap motor bypassed with 4.7kohm resistor.
Intercooler pipework checked
PCV rear seal changed
MAF sensors input/output checked
No signs of any air leaks (although could do with a proper smoke test) - testes with smoke on outside looking for air suction.
Turbo vanes free to move and actuator functioning correctly and receiving correct voltage.
Voltages checked on above sensors
Scan shows pressures flow etc all correct
DPF has ash content of 0.01g and soot content 4.51g, so ok
Have discondected battery and allow ecu capacitors to drain to reset ecu
Supply from ecu to above electrical components all correct at either 12v or 5 volt where required.

All this and I have the same problem still!

#Odd thing though, the first air temp sensor I fitted was a generic one which was meant to be suitable for this car but it gave a code for it. After fitting it the P0402 went (well briefly at least). I put the old original temp sensor back in and the temp sensor code went but the P0402 returned. I am currently waiting for a MB Temp A6511530028 sensor.

If there are any geniuses out there I would appreciate any help.

Cheers

 

[whitenemesis]

Star or generic code reader?

 

[serow]

Creader Viii Launch

 

[W1ghty]

Visit to an MB specialist , ideally before you changed all those parts which were not necessary if the original fault still exists ?

 

[serow]

Possibly correct, EGR valve needed changing though. The sensors likely not but it was a quick way to comfirm. Having said that, I just should have checked them via backprobing. But at least I know know what is good.
Thanks.

 

[serow]

One thing I need clarity on though is the talk of clearing the ECU / or ensuring "adaptaion" of the new parts. I might have thought that disconnecting the battery and discharging the ECU might have the same effect, but I could be wrong. There are many instances of dicussions about re-adapting via Star or other capable scanners.

 

[W1ghty]

Possibly correct, EGR valve needed changing though. The sensors likely not but it was a quick way to comfirm. Having said that, I just should have checked them via backprobing. But at least I know know what is good.
Thanks.

Don’t get me wrong , I’ve changed parts as a best guess to repair the fault option , I’ve no problem doing that , especially if it’s a part that will need changing at some point .
I have with my icarsoft been lucky so far .
If the part is £50-100 region which is what a Star session might cost I would change it and see .
At some point it’s then Star and expert time

 

[serow]

Update -
Proper smoke test of system today. no leaks at all.
The pressure control valve pins (two pins) have direct continuity between them. So the voltage is the same for both of them when connected 12v. Should this be so? Seems odd to me. The plug itself, when disconnected, has one terminal at 12v and the other at 3.5v. Any thoughts on this? Cheers.

 

[serow]

SOLVED!!
Got my MB WIS working on laptop an accessed circuit diagram for EGR and associated items. This is how it went ....
it seems the egr shares a connection with the throttle actuator and the cam hall sensor and the crank hall sensor. So I'm going to check for continuity and the shared connection points. Would not be surprised to find the sensor ground (shared between egr and and throttle actuator, connected to pin 5 on ecu), with having a problem. Y27/9 is the EGR, M16/6 is the Throttle actuator.

Tested continuity between pin 4 egr to pin 2 throttle and all was well. Tested throttle output to ecu at idle - ok at 0.4 volts, revved engine expecting voltage to increase up to 4.5 volts. No increase found, it stayed at 0.4 volts!! So this is the fault of it all, throttle sensor output to ecu not working. It's like this - throttle is moving so lets in a lot of air as you open the throttle but the ecu is being told by the throttle sensor that the throttle is still closed. ECU now has conflicting information, all other sensors read massive air flow but computer sees closed throttle - the two things don't match up - it sees an excess air flow - hence the P0402 excessive flow code!!!

The position sensor is part of the throttle body and as the butterfly valve opens to allow more air into the engine, there is a gear drive from the throttle motor to the sensor. I dismantled it this morning and it seems like one of the contact tracks has failed. (It's just like a dimmer switch really). Its working as a potentiometer at the very start of the graphite track only and not along the ehole track. So this fits with the finding that the voltage is only being read as the starting voltage.
Clear fault verified. I'd been searching for a wiring diagram for ages, had some issues with the WIS on the pc but got it sorted. Always have a circuit diagram to hand - makes life a lot easier!
New part on its way this week.