So ive been troubbleshooting like a maniac for the last couple of weeks.

My c220d 2017, enters somekind of limpmode when you press the gas a bit harder and when you turn the car off and on again it goes back to normal.

First i thought it was some weird software fualt since I have an adblue delete software. But with help with an expert we restored it to the original software to rule that out. Still it kept on entering limpmode.

I have meassuerd boost preassure, injection timing and those are normal.

We pulled the codes after entering limpmode not turning off the engine and we did it while it was turned off.

It gave 2 codes once and they never came back.

P019300 The Rail Pressure Sensor Has A Short Circuit To Positive.

P012315 Position Sensor 1 For The Throttle Valve Has A Short Circuit To Positive. There Is A Short Circuit To Positive Or An Open Circuit.

According to the Mercedes where I live i need a new common rail for 1400€ ish. They dont sell the sensor sepperatly.

Has anyone had any similar symptoms or any tips What to do now, im not payin all that hahah.

Im gonna check the sensor connection itself and the wireing this weekend to see if i get the correct voltage.

Sadly i only have access to an autel reader and the Mercedes workshop only have time to troubbleshoot in 5 weeks Xd.


english is not my first language so im sorry if its misspeld and Thanks is advance.

 

You are getting a reliable limp-mode driving you mad with limited local options.
You should book the next available appointment at your dealer and hope you can get this resolved in less than 5 weeks.

You've managed to pull two significant faults.

Do you know the meaning of "short to positive" ?
There's a tall chance you're simply dealing with unreliable painted GND source.

Request your MB Specialist to Clean up poor GND post connections in engine bay + footwell. In addition get the chassis voltage checked under the same conditions when faults take place.

 

Hi! Thanks for the reply .

Im not so sure what that means no, but I think it means that a earthwire carry positive volt or am I lost? Hahah i usually stay away from anything not mechanical.

Anyways ive been troubbleshooting some more and Ive come to the conclution that the code for the fuelrail sensor only comes when the ECU has been dissconected.

And ive checked live data from the fuel preassure and its seems to be working as it should. Ill post some pics from the live data.

Now im leaning towards a fualty MAF sensor or something else with the airflow. Still get no codes when its in Limpmode and it only happens when you press the gas hard at higher speed and rpms.


I tested driving without the MAF connected and it drove like **** ”surpprise” but it did not go into limpmode like it does with its connected. I tested cleaning it with a ”massairflow cleaning spray” still not working.

Ive orderd a used MAF for 100$ since a new one from Mercedes cost around 450$. Just to be sure that this is the problem.

I keep the car on the lift and drive the company ****box until I leave it on 10 november when the MB specialist have time. But hopefully its the MAF sensor thats not working like it should. Otherwise i Will do a smoke test and check for cracks.

unless anyone has any other tips on what could be the problem.

Idle.

Before it enters limpmode.

Limpmode.

 

Good job: you have captured data supporting your issue...


is 25kPsi good pressure ??

Get the fuel rail SENSOR circuit looked at - It is feeding bad voltage that ECU reads as wrong pressure.

This may be a wiring issue or sensor needs a genuine replacement.

 

Im getting everything looked at on november 10!
and Im not driving the car until then.

Im not a pro, im just a 20 yearold wheelloader operator Xd, i work on cars in my freetime to save money since i choose to Buy a benz lol.

Theese are screenshots from a video, its hard to pause it on the highest readings. The railpressure gets up to 29k psi.

Could it not be that the MAF sensor is going bad and reads faulty airmass and that makes the ECU compensate with lower railpressure? And then the car enters limpmode.

In the video the MAF reads 0,32lbs/s just before limpmode and it goes down to 0.17 before the railpressure goes down. And then enters limp.

Ive read that its suppose to be higher than 0.32lbs/s and that could cause the ECU go loco.

And since when i tried driving without the MAF connected and the ECU was forced to read the ”defualt” airmass it didnt go into limp.

Im willing to try swapping the MAF for 100$ to be sure that thats not it. Since you cant just switch the railsensor.

You need to Buy a whole new rail for 1400$. They dont sell them sepperatly. You could get a used rail for 500$ but thats a gamble.

And ive backprobed the fuelrail sensor.

It reads with ignition on pin 1, 5v, pin 2 (ground) 0v, pin 3 0.5v and with ignition off its reads 0v on pin 3. Thats the pin with the signal wire.

and with the car on Idle it reads 5v, 0v, 1.2-1.5v.

Tried to pull on the wires a little when reading and the values stay the same. Thats all i can do with my knowledge . From what ive read those values are normal. But idk

Edit* im going to buy a testlamp and see if it powers on if i put it on pin 2 and 3. If it doesnt turn on does that mean that ground is good?

And the new used but fully working MAF sensor arrives on friday so i Will uppdate then.

 

I had overlooked... this is a diesel with rail presure way up to 1600.Bar (23k.Psi)
Your good back probing work confirms a working harness connection to ECU +5VDC.

++++ In addition:
You said disconnecting the rail sensor is what caused the code: yes, highly likely.

"P012315 Position Sensor 1 For The Throttle Valve Has A Short Circuit To Positive. "
What about your Throttle valve fault, also disconnected or really faulty? That one can really earn a quick limp-mode.