Crunch69

iTrader: (1)

Looking for help concerning Permanent DTC P2540 with no Check engine light. Recently we solved a P0087 thank you everyone a couple of days later after that repair I thought I would perform another scan even though I had no idiot light. much to my surprise a Permanent P2540 showed up and has been haunting me since. The gift that keeps on giving.

Looking for voltages and ohm measurements of the low pressure sensor as well as voltage measurements from the low pressure fuel pump. A schematic would be a great help.

Is the Permanent DTC P2540 generated only from the low pressure fuel sensor B4/7 or could it be something else?

Note: The the passenger side fuel pump assembly is new the driver side pump filter assembly and low pressure fuel sensor are new.

Both the old and new sensor throws the fault code could both be bad?

At idle the low pressure sensor B4/7 has 4.93 volts on pin 1 and the signal pin w2 has 2.50 volts

What voltages should I see at the low pressure fuel sensor hen ignition is turned or if the car is at idle?

Are there any resistance measurements across the sensor that will show a good from a bad sensor?

If it is possibly the fuel control module what are the correct voltages I should see in and out?

I did make a few measurements which I think are incorrect and would like to validate in the attached pictures. If they are incorrect I will need to know were the are generated from

Thank you

Crunch

CaliBenzDriver

Do you think this code could be triggered by a false measurement ??

Have you looked inside the controller module by any chance... (under rear seat) ?

S-Prihadi

As per your PM to me, but based on my VIN for Fuel Control Unit module N118 which WIS/EPC stated for M276 and M278, attached all I got on it.
Original XPS document zipped.

Have a look.
Note : Fuel Pump uses PMW signal, so ordinary voltmeter is not suitable. The fuel pump motor pins 2,3 and 4 are the V,W,U ............so it is a 3 phase motor too.


01. What kind of scanner are you using ?

02. You say permanent P2540, but CEL/MIL is not triggered yet. How many times have you cleared it ?
Usually before becoming a CEL/MIL, an ECM has to register the fault a few times.
I don't now how MB manage the threshold to qualify a CEL/MIL.

03. Here I am confused. Please verify which 2 pins you are actually refering to ? I hope its pin 5 and 6 only, the ones you are measuring.
The Pin5 at 10.45 volts, measure against which pin ? or perhaps to ground ?



Pin 5 and 6 are connected to Rear SAM N10/2 and not the Fuel Controller Unit N118.
Yes, they share that 7 pins connector as per diaghram.
I attached Rear SAM N10/2 sheet 5 diaghram which you will need .

.

S-Prihadi

Try reading this :
https://www.benzworld.org/threads/p2...zNA2KjcnBszQhO

Who knows it may help.


Also is your sensor + all parts you mentioned being new/replaced, are they original from MB or aftermarket unit ? , regardless that it is the same model from same brand supplier as MB.

Crunch69

iTrader: (1)

S-Prihadi thank you for the documents

Can anyone confirm pin 2 signal voltage (2.50 volts) at idle on the low pressure sensor?

Concerning pin out of the fuel pump plug is the brown GND wire suppose to be pin 1? I was starting with the white dot as pin 1

01. I do not have a scanner.

02. You say permanent P2540, but CEL/MIL is not triggered yet. How many times have you cleared it ?

I have cleared it at least 10 times in the last 3 days

03. All measurements were made from GND. The 10.45 V was with the plug unplugged. It was the purple wire Now knowing this is controlled by PWM the voltage measurement I believe is moot

I read the document in the link it states

P254000 The signal for the pressure sensor of the fuel low-pressure circuit is implausible

Cause:
Internal in tank leakage of the assembly of the fuel pump module

If this is measured by the low pressure sensor what signal voltage is plausible?

I have no idea were to start or how to troubleshoot Internal in tank leakage of the assembly of the fuel pump module except to swap it out.

I have swapped the older original assemblies back in and even put the new assemblies in with only original sensors.

Both assemblies are aftermarket bought from Amazon. I cannot see how that can be the issue since I have swapped my old stuff back in and even put the new assemblies in with the original sensors. I have done this so many times I can now swap everything out (both assemblies and sensors in 15 minutes.) I have been up to my elbows in gasoline for 4 days.

Is the P2540 triggered by the B4/7 low pressure sensor and if it is that is the correct signal voltage on pin 2?

S-Prihadi

This is the way I interpret the : P254000 The signal for the pressure sensor of the fuel low-pressure circuit is implausible
The "signal" to me would represent a pressure value, of which it is the result of 2 components working together.
1st the fuel pump being commanded to spin at X rpm and produce Y pressure value. Y here is a true mechanical pressure value.
2nd is the pressure value at the sensor B4/7 output in electrical value, derived from mechanical pressure value.

The N118 fuel control unit knows (based on clean fuel filter ), that at what RPM/speed the fuel pump would generate how many psi. It surely has an rpm vs pressure table if not amperage + RPM vs pressure table
So these 2 conditons can cause the P254000 code :
AA. A defective or not suitable Fuel pump commanded to an X rpm not producing expected fuel pressure ( assumed sensor is healthy )
BB. A healthy fuel pump commanded to an X rpm, but a defective sensor is reporting a value out of the tolerance of the table in the Fuel Control Unit's table.


Page 45 of the M276/M278. Page 46 if in pdf



The fuel filter and pump assy which you replaced with aftermarket product, has 3 components which produce "values"
B4/1 and B4/2 which are left and right side fuel level.
M3, that 3 phase low pressure fuel pump motor.


B4/1 and B4/2 which are left and right side fuel level. These are using potentiometers to produce values.
Fuel tank fill level sensor, basic function - gf4750p2000a
I dont believe these can cause P2540 code.


M3, that 3 phase low pressure fuel pump motor.
I am afraid this aftermarket pump or fuel filter element, or both..... could be "incompatible" or under-performing. 4.5 to 6.7 BAR or 65 to 97 psi, this is the expected pressure.
You reported only 60-70 psi, is this idle to WOT or only at idle ?



You mentioned :
I have no idea were to start or how to troubleshoot Internal in tank leakage of the assembly of the fuel pump module except to swap it out.

I agree with you, that leak can also cause low fuel pressure.
Below in green is if leak occurs there, in red is if blockage occurs there...... low fuel pressure can result.



I think now, priority 1 is to make sure, mechanically verified you are getting as close as possible to 4.5 to 6.7 BAR or 65 to 97 psi at the hose output of the low pressure fuel pump.
I added some more information I managed to dig out from WIS.


Happy troubleshooting.

Crunch69

iTrader: (1)

Fixed not exactly?? Note the pressure we are looking for Low side 4.5 bar/65 PSI to 6.7 bar/97 PSI and High side 117 to 175 Bar

I installed a new manual pressure gauge on the fuel rail with the aftermarket drivers side Fuel pump / filter and aftermarket passenger side low pressure fuel pump both using Mercedes OEM sensors in this all aftermarket assembly's at idle up to 3000 RPM measure 4.5 bar/65psi - 6.5 bar/95 psi on the high pressure fuel line when driving measures 117-175 Bar. The low pressure sensor signal line measures approximately 2.50 volts on both the old and new aftermarket. If you floor the pedal the high pressure recovers very quickly. Even though this configuration the pressures are on point and very stable and the car runs strong it produces the dreaded DTC P25400

Here's were it becomes odd leaving the new aftermarket fuel pump installed and reinstalling the old 90K mile drivers side fuel pump/filter at idle up to 3000 RPM I measure 4.48 bar/60psi - 5.17 bar/75psi 20psi lower and on the high pressure fuel rail when driving measures 115-169 Bar slightly lower than it should. The low pressure sensor signal line measures approximately 2.30 volts on both the old and new aftermarket. The high pressure measurement bounces around and is not as consistent as the all new aftermarket parts configuration. Yet this configuration with the old filter that I think is partially clogged produces no DTC's ???

With these lower than normal measurements I believe are caused by the old driver side pump/filter so I have a new driver side fuel/pump filter on order to see if the one I have was defective Note With the older pump/filter the engine did not run as well as it did with the new filter

S-Prihadi

Hi Crunch,

The fuel pressure sensor is OE and working. Noted.

Is this table I made below correct ?



Indeed a unique case you are having, if the troublecode is supposedly only P254000 which is pressure related...supposedly.

I think you need to do a simple float level test ohms value now.
Doesn't make sense..... but .. best to try.

Both floats, original and aftermarket ones.
Out of the tank. Test float at maximum lowest, middle and maximum highest.
Use highest resolution ohms setting, because this could be a few hundred ohms differences only the max-middle-min reading.


BTW,
You said you do not have a scanner, so how have you been deleting/reading the troublecode ?

I found this document. Have a read. It is the PMW fuel pump being discussed.
https://automotivetechinfo.com/wp-co...z-Vehicles.pdf
I find their amperage data a bit too much though, because the N118 fuel computer get only 20 amps fuse and I would think N118 maximum consumption would be highest at 15 amps.

Actually , I was more suspecting the aftermarket fuel pump as the issue.
The pump being a AC type PMW speed controlled can be monitored with ease by the N118 Fuel Computer , RPM, duty cycle, amperage and so on.... as such if RPM of the pump or the amperage of the pump
does not match the N118 stored 'mapping" value based on X duty cycle, it may deemed pump as unhealthy.

If you take a look again at the Xentry data I linked. The guy had P254000 at 70% on/off ratio of fuel pump ( duty cycle ) while only taking in 6.20 amps. RPM of pump at 5,350 rpm and pressure at 89 psi.
If the MB-Smart-Power pdf I just linked is accurate on the RPM info, 47% percent duty cyle they get 8,350 rpm....massive difference.

.........

S-Prihadi

I forgot to add this :
https://www.justanswer.com/mercedes/...enz-ml320.html

The importan point here is :
Wire harness of N118 was damaged. yada yada.
New pump was also damaged simply from wire harness which was not repaired when new pump OE one installed...within 500 miles of use.

CaliBenzDriver

OMG Surya, you did it again: you dug up the best documents to help us focus.
THANK YOU, THANK YOU !
👍

I just got done meeting with the fuel regulator module. It is a good guy, the PCB itself should be long lived.

Your documents match the power control I discovered: 6 nice power MOSFETS layed on the circuit board.
Now that I've just read (thanks Surya &#128077 that it is both PWM *and* Frequency modulated. Continental really threw the whole book at this state of the art 3-phase AC pump. The pressure from this fuel pump directly feeds the high pressure pump intake. The ECU controls it to help the HPP regulate the rail with its own PWM control mechanism. Obviously this is super cleaverly done with boat loads of ingenuity (ECU, SAMS, sensors and multiple pumps...). The best industrial pumps are 3-phase units to allow for ramping and precise speed control.

In other words this low pressure pump module is really a VFD controller... that is a luxurious design 👏


Pump Module controlled by ECU and both SAM's


the whole story: "...acts up on LONG DRIVES": small world!

You know what I'm gonna say....CHECK YOUR GND's and join the party

The fact that this happen on "long drives" points to not only GND or low DCV but CAN disruption courtesy of SAM's not enjoying higher current with 3-phase PWM noisy spikes! When the pump controller finally crashes the engine reportedly stalls and before that flaky DTC'S.

We need a geek session with the electric WIRING DIAGRAM to look at the pump vital connections.

I merged some of the fixings to prevent dups. Look here for more... post#75.


Like tech entertainment ? Take a minute to look at the TSB content in this LP Pump thread (if the tank is not empty replace it)

S-Prihadi

Yes, I hope this is getting closer for Crunch to solve his issue ................

Short of a Xentry scanner, we can only speculate.




What if the resistance/ohms value of the fuel level sensor of the aftermarket fuel filter assy and/or pump assy is not inline with the car computer expectation or calculation table ? ...and it throws a code , but only P254000
Look at the 3 explained probable cause of the fault code in the TSB above , all are PRESSURE related, none is about fuel level actually.
https://mbworld.org/forums/attachmen...1013_ver_1.pdf

Look at the work units damage code (corrective measure), the one I marked green is related to the level gauge section, which is not Pressure per se, but fuel quantity at the tank.

OBD protocol has trouble code for fuel level, but MB might not want to use that...who knows ??

Diagnostic Trouble Code (DTC): P0463

P0463 code definition

When the powertrain control module (PCM) gets an input signal from the fuel gauge (or fuel level sensor) that is higher than the actual level of fuel in the gas tank, it will store a P0463 code, and the Check Engine Light will turn on.

Looking at my limited capability icarsoft MB v2.0 scanner, some troublecode do not make it to CEL/MIL at the instrument cluster, example is removal of the alternator LIN wire.
Perhaps not an urgent type, so it is simply stored and can only be visible when I use the scanner. My scanner being stupid, cant detect the trouble code in auto scan mode, must do manual mode .....hahahahah.
I don't know why, except it is what it is.

Here we maybe facing troublecode based on electrical values and not mechanical values.
Since the car computers only understand voltage, resistance, frequency and whatnot.................. it wants to see those values as per their stored table.

Since the car itself with the current P254000 code appearing, is actually VERY driveable, aka healthy.............. we are now trying to satisfy the computers, not the mechanical well being
of the car engine + fuel components which seems to be in good shape.

If we approach this problem from a very "analog" and very mechanical mindset, we probably will get pissed

CaliBenzDriver

At this point it's fair to assume nothing is broken, the sensor, wiring, pump check out and work ok yet it keeps falsely reading a LP code.

The available TSB are inconclusive or misleading towards tank being empty...

I see s possibility the R-SAM is reading noise as being actual signal.
The pressure sensor circuit reads around 2.5V. That is not much room compared to a noisy 10kHz at say about 10VDC (?)

I've not yet experienced any W212 fuel issues, knock on wood. I think the flaky 12.6v float control shares a commun theme of skewed measurements by R-SAM.


Long story short...:

- check GND's for FP + R-SAM

- physically separate noisy wiring: sensor, power.


I have already separated my pump side wiring, next I'll separate +12 pump module feed from R-SAM.

Twisting the sensor wiring is also a great idea (just like CAN wiring) while dealing with the route between R-SAM to pump controller.


There is one stupid detail that ties everything together... what is it

CaliBenzDriver

Read low fuel pressure live data to compare the reported pressure with noisy pump running vs. immediately after stop.

Any significant difference shown??

If PWM electric noise is involved..., running pressure should read differently (lower?) than without pump noise.

Normally both values should be extremely close.
✌️

++++++
Is acceleration affecting LPP control???
Higher gas demand triggers higher pump RPM to supply the HPP consumption.
Higher Amps create greater pump noise that affect the control loop.

Based on a E63 video, I believe LPP output pressure should be nearly stable regardless of demand. The Pump RPM varies to deliver a steady pressure without "pressure boost" effect... only one single flat low pressure.

S-Prihadi

Bloody hell WIS/EPC , its search engine is really bad !!!!
I finally found the fuel system document with proper data, while I was looking at CAN BUS !!!

How the hell it was not included during the fuel system search a few days ago ?????

Crunch & Cali, find the IMPORTANT parameters value in the M157.9 fuel pump PDF.
I wonder why the same fuel pump system on M276 be it 3.5NA or 3.0TT does not have that important table ??? Hello MB...????

CaliBenzDriver

specs

This shows low pressure (capacitive ie. contactless) sensor works off the 5V reference, from 4.5v down to 0.3v.

The pump PWM alone is 1/2 of 12VDC (not factoring ringing spikes)... so very significant when compared to sensor input around 2.5VDC.

>>> Spreading apart the FSCU wiring sounds like a pretty gooood idea short of shielding pump lines.

​​​​​​+++++
Sometimes next week(*), I am going to scope the harmonic pump noise to quantify it:in the 3x phase lines
In the 5v Ref. line to both Sensors.
in the 20A feed near module and near R-SAM.
In the GND near module.
(*) UPD: I can't run the pump without the engine 😭

Crunch69

iTrader: (1)

S-Prihadi now you see why I am losing hair see the updated chart below. It looks like the filter assembly is were the pain is I will know soon as I received a new aftermarket filter assembly today from a different manufacture just need to lower the fuel level in the tank a bit before installing it.
I think the first vendor may have sent me the incorrect filter assembly 2184700194 when I need a 2184700994.

I do have a mode 6 scanner I thought you were speaking of a scope to measure PWM.

S-Prihadi

This is interesting Crunch.
BTW, aha.... so the fuel level sensors both side are separate items from the fuel pump and filter assy yah. Good.

Now we must start wondering : how does a non electronic/electrical aftermarket fuel filter assy.... can contribute to trouble code ?, while its pressure is better than the OE 90K old filter assy ?
Is it still the power vs rpm profile of the aftermarket pump and its pressure curve as read by OE fuel pressure sensor ....or what ?
This is a good case study. Let see what happen when you install the deemed correct version fuel filter assy 2184700994
.

Crunch69

iTrader: (1)

Quick update this is still throwing me for a loop after installing the new driver side suction pump/ filter assembly I am still getting a pending P2540. I also tried switching out the original fuel pump with the new driver side pump with no difference. when the new right and left side pump assemblies are installed there is a noticeable performance gain when you floor the car. I think this is due to the higher fuel pressure getting more fuel into the cylinders and when both original assemblies are in I have a few misfires on start up due to lack of fuel? Since this is only pending DTC i am going to drive it a bit with both new assemblies. The only part I think it could be but could not swap out to test was the suction pump. Each has a little difference in the way they use o rings to seal to the filter making it impossible to switch that part out

S-Prihadi

Well, drive around on your best set up for say >500+ miles. Let see if P2540 will stay or will go away when certain cycle met.
When it comes to software/coding/algorithm whatever they call those programs, the computer decision to issue P2540 while your butt-dyno can feel healthy condition is what we don't understand.

The P0087 I think its a different set of problem, which you have solved and has never come back or produce the mechanical issue it caused some weeks ago. Case closed.

The good thing is, if any troublecode does not become Check Engine Light, I guess it is low level urgency...if indeed it is a true P2540.

P2540
The P is Power train, the 2 is OEM specific, the 5-4-0 is then no more OBD2 generic standard.
Only when 2nd character is zero ( OBD2 generic), the rest of the characters that follows are then from OBD2 generic database which I think SAE is in charge for the updates and standardization.

P0087
The P is Power train, 1st zero is generic OB2D sentence, 2nd zero is air fuel mixture related. 87 is the description.

https://www.outilsobdfacile.com/data...tc=p0000-p0299
https://www.outilsobdfacile.com/data...tc=p0000-p0299

Klavkarr is professional company, so their data source is credible.

CaliBenzDriver

3000 rpm pressure equals that of 700 rpm

It looks like the LPP output is regulated regardless of rpm change.
Min 60Psi
Avg 65Psi (4.5Bar ; +/-0.3)
Max 70Psi

The acceleration enrichment is done by injectors duty-cycle for extreme granularity control, not by boosting LPP pressure.
🙂

Your wide pressure variations are a bit puzzling. Either the pressure sensor is reading wrong -or the pump control is inadequate -or CAN-C datagrams between ECU to FSCU are delayed... I am sure you're not alone with pressure swings.

RETURNLESS PRESSURE CTL:
Isn't the pressure regulated mostly by the "ball on spring" return control has it is done conventionally on returnless fuel injections.
The pressure sensor is then only a cut-off control.

I don't think you can build a reliable pressure regulation across the CAN!! Pressure sensor is wired to ECU, Not to the FSCU.


If pressure is too high (95psi) the filter housing that host the spring-ball is faulty or reading is questionable.
✌️

Tutzi

Hello,

my name is Sascha and i came from germany. I have a Mercedes S204 C-class 2012 with M276 engine.

I want to ask if the problem of crunch69 has been solved? At first i had a mistake in the engine P008700 - fuel pressure low. This mistake happened very rarely. First i changed the fuel-filter against a new one from producer HELLA. (not origin) Now i get all the time the mistake in the N118-Control Unit with P25400 but no checklamp and no abnormalities during driving. After this i changed the intank-fuel pump with a new one from Mercedes-Benz. This mistake is still there.. My guess is, what the mistake is caused by the Hella-fuel filter. Maybe the original filter from mercedes is a little bit different to the aftermarket filter???

I also noticed that the mistake occurs not in moment of acceleration, but only in the moment of thrust there the engine do not need fuel... (i saw that in the error code freeze frame data)

Do you have any ideas for that???

S-Prihadi

Sas,

01. What is your Low Pressure Fuel ( sensor at fuel filter housing ), under N118 fuel Pump module in Xentry ? Do idle and rev 4200 maximum soft limiter.
02. What is your High Pressure Fuel Rail pressure at idle and at 4,200 RPM soft rev limiter, car not moving, be stationary is ok. This is under N3/10 engine computer,

Later you will need to verify 01 with manual pressure gauge, as you would see in my links.

P008700 as you have access to Xentry, mentioned High Pressure fuel pressure is lower by 24 BAR compared to target for longer than 3 seconds.
Unfortunately we do not know what is the TARGET/COMMANDED fuel pressure, the N3/10 engine computer only shows actual fuel pressure, but not TARGET/COMMANDED.


P254000

Did the non original Hella fuel filter has its own new fuel pressure sensor ? Or you use the old one from the old fuel filter ?



I am confused looking at the freeze frame because it is in German and I do not believe in Google translate
It seems to show Low Pressure fuel data, because it has the fuel pump RPM and lower reading of 4.5 absolute fuel pressure and 7.05 BAR fuel pressure.
The fuelburn 0.0L/100KM no need to worry, at idle those data are useless.

Regarding fuel system, Low and High, take a look here :
https://mbworld.org/forums/e-class-w...er-change.html
https://mbworld.org/forums/e-class-w...el-system.html

Assuming your fuel pump in tank and the fuel filter is good, there are only 2 other possible mechanical issue ;
01. High Pressure Fuel Sensor ( with temperature ) faulty or under-reporting
02. High Press fuel pump defective mechanically or its quantity valve.

.

Tutzi

Hello,

thank you for the answer. I will check 01 and 02 and give you the data in english.

The Freeze Frame is from the mistake in the low pressure system. the high pressure system has no mistakes since i changed the fuel filter in the low pressure system. But directly after changing the fuel filter it comes the P254000 mistake (without any abnormalities and mil-lamps). Thats why i think the mistake is caused by the aftermarket filter. But i'm scared to get no success with renewed change with an expensive mercedes-filter.

The Hella fuel filter has a new pressure-sensor. After first time the mistake appeared, i changed the sensor with the original sensor, from the old mercedes fuel filter.

To make it clear. The mistake doesn't come at idle. The car is rolling on street. The car pushs the engine (fuel is not needed).

I will make today the tests and give you more informations.

S-Prihadi

Sas wrote :
To make it clear. The mistake doesn't come at idle. The car is rolling on street. The car pushs the engine (fuel is not needed).
Aha, I see, I think you meant that the car is coasting ( like going dowhill and accelerator not pushed down ) , aka car PUSH engine...Okey, I got it. No wonder 1,350 RPM.
I thought you are at stationary and rev up at idle to 1,350rpm.

Okey, now the DTC (mistake/error code) explained that P254000 is when the Fuel Pressure Sensor value DOES NOT MAKE SENSE or higher than 10 BAR
DTC also explained, there will be no MIL or Engine check light actuated for this DTC
DTC also explained the signal is OK, but the value (pressure/BAR) is the one which DOES NOT MAKE SENSE <<< this one is saying that it seems the issue maybe a mechanical one instead of an electrical one, but don't make any assumption yet.

If the Laptop where the Xentry is at can be installed a screen recorder, it will be the best tool because you can record live Low Fuel pressure data while engine is under load aka proper road test.
If laptop is Windows 10, it has its own screen recorder under the gaming feature. Press the Windows Icon button together with G, then the screen recorder will appear. Make sure Xentry is in full window size.
https://www.tomshardware.com/how-to/...ord-in-windows
That is how I record my N118 fuel data while on road test because to see say a 0.5 seconds occurence of that 10BAR fuel presssure, you need the screen recorder.
Freeze Frame is not always super reliable data.

Now, if you read my link well on the fuel filter change, I explained that there is a 55/2b pressure regulator or a relief valve or overflow whatever best to call it,
which supposedly will maintain no higher than 7.5 - 9 BAR of fuel pressure. If indeed your fuel pressure can exceed 10BAR, this 55/2b is most likely the bad boy.
However...This we can confirm only if your test using Xentry and later maybe using mechanical fuel pressure gauge indeed proved 10BAR+ of fuel pressure did happen.








This is 55/2b

S-Prihadi

Sas,
One more thing. We help you, you help us too..okey.
Cut open your old filter like I did. Show us how dirty it is for you to initially get the P08700. What is your mileage on that filter too, please.
Thank you....

How comfortable are you with electrical troubleshooting ?
If mechanically there is no 10 BAR pressure ( mechanical gauge), you need to divert attention to electrical troubleshooting the LP fuel sensor and its wiring.
You will need a probe kit ( like needle ) and a video camera to video your voltmeter during a test drive, unless your voltmeter can log at least 1 data point per 0.5 seconds.