2014 E250 CDI Limp Mode Issues without Any Faults

[Mene]

I have a 2014 Mercedes E250 CDI convertible version and suffering a limp mode issue since last 5 months. It started in April 2023 while I was driving the car high speed, the car lost the boost and the engine light turned on. I took it to the mechanic and he told me there is an issue with the EGR. As he suggested, instead of replacing the EGR, we have completely removed the EGR and they tuned the ECU to not to use the EGR anymore. In the meantime they told me there were a couple of issues in the ECU as well and they repaired it physically as well. After I got the car it started good, but then after 5-10 min later, the car lost the boost again without giving any faults. I got the car to the mechanic again, he connected it to OBD2 and no errors seen. We switched off and on the engine and the turbo works flawlessly, no issues. I took it back and drived again but after 5-10 min later and the car goes into limp mode and there were no boost anymore. Whenever I turn off and on engine, immediately it works perfect, but after I used it a bit hard again it goes to limp mode. I got the car to 4-5 different mechanics. Nobody figured out why it is making like this. They checked the ECU again if there were a fault during the reprogramming but as the mechanic told me, the test values of the reprogrammed ECU is perfect, no issue from the software. As I'm living in Malta, unfortunately there is not so many good mechanics option here.

So, 5 months passed, the car still in the same condition. I'm using it daily around 100kms. If I don't push it hard and drive slowly nothing happens to the turbo/boost. But if I drive it fast, NOT in the first time but after a while it goes to the limp mode without an error. How can I sort out this issue? Is there anyone who has sufferred the same thing and sorted it out?

 

[malcolm E53 AMG]

Welcome!

Has the car been tuned?

 

[Mene]

nope, no motor mod/tune has been done except disabling the EGR

 

[supernoodle]

So you've had some dodgy software put on the ECU and someone has made some "repairs" to it. There's the problem.

 

[rf065]

I had a CLK220CDi with the same fault, turned out to be a split intercooler hose.

 

[Mene]

I had a CLK220CDi with the same fault, turned out to be a split intercooler hose.

did your car gave any errors when you connected it to OBD2 or there were no errors?

 

[Mene]

So you've had some dodgy software put on the ECU and someone has made some "repairs" to it. There's the problem.

I tried it with another guy and he got the original software from web and then amend it with removing EGR. same issue still happens, so most probably it is not from the ECU software. cause it doesn't give the error everytime as well.

 

[ajlsl600]

Find out if any issues prior to egr delete. Start from there
Cud still be boost issue as until you push the motor it can cope maybe without opening up a boost leak issue.

 

[malcolm E53 AMG]

I think you need to get the ECU back to factory settings and reinstall the EGR and go from there otherwise you don’t have a good base to work from. The only other instance I can recall on this forum with the 250cdi engine where the car was behaving the same as yours was after an ECU tune which resulted in a fuel rail pressure problem causing the engine to lose power at higher revs, the fault couldn’t be rectified by the tuners so the ECU was returned to stock and the engine behaved as normal

 

[rf065]

did your car gave any errors when you connected it to OBD2 or there were no errors?

No errors, no warning lights. On this and other forums I was assured I could not be in limp mode without the engine management light being on or error codes in the ECU. Mercedes basically said dealer said no light, no codes, we don't believe you. This lasted for 2 years until the frequency increased and finally the engine light came on and generated a fault code, Mercedes dealer said I needed to replace the intercooler hose and the car never went into limp mode again!

 

[JoeHorner]

Were the codes read with a standard OBDII reader or a specific Mercedes one?

There are plenty of "marque specific" codes that a standard reader won't pick up on these.

 

[Mene]

we have used 4 or 5 different OBD2 reader from entry level to high level but as far as I know all of them generic models, which works with every brand.

 

[rf065]

Were the codes read with a standard OBDII reader or a specific Mercedes one?

There are plenty of "marque specific" codes that a standard reader won't pick up on these.

In my case, it was the Mercedes Dealer who said there were no codes.

 

[JoeHorner]

we have used 4 or 5 different OBD2 reader from entry level to high level but as far as I know all of them generic models, which works with every brand.

You really need to get it connected to (ideally) an xentry set-up or (at least) something like an Icarsoft MB specific reader. Generic readers will often ONLY report codes related to the mandatory OBDII system which all recent cars need to have. But those are almost all emissions related and don't cover a lot of potential drivability problems.

Xentry is fantastic because it'll report every sensor on the car, including ones that are "hidden" from other readers, and also includes guided faultfinding test according to symptoms.

The brand-specific ones are somewhere in between the two. They'll give a lit more data than a general scanner but nowhere near as much as Xentry.

 

[JoeHorner]

In my case, it was the Mercedes Dealer who said there were no codes.

In case of a split hose it's likely the code was resetting itself "on time". Should still have left a stored code but they may not have checked those thoroughly. For proper diagnostics they SHOULD have reset all current and stored codes then either test driven until it went wrong or handed back and asked you to return when it played up again. Any new current OR stored codes would likely then be relevant.

But that's time consuming!

 

[JBell]

You need to have the car "Live Diagnosed" i.e. when it goes into Limp Mode take it straight to the garage and DO NOT turn it off, get them to plug it in with the engine still running and diagnoise from there

 

[Mene]

You need to have the car "Live Diagnosed" i.e. when it goes into Limp Mode take it straight to the garage and DO NOT turn it off, get them to plug it in with the engine still running and diagnoise from there

I already did it but still nothing seen. I tried with 3 different OBD2 devices, one of them icarsoft

 

[JBell]

I already did it but still nothing seen. I tried with 3 different OBD2 devices, one of them icarsoft

You need Xentry to get it done properly

 

[supernoodle]

I read on here lots of talk of "limp mode" but no fault code. It is quite possible you have some failure that is causing a torque limitation without a fault, I would not call that "limp mode".

The inputs from the sensors all feed into the ECU calculations of available torque. The max torque output will be the minimum of all the calculations. So if one of those sensors is giving spurious readings, but in range so not giving a fault, you can end up being limited in torque.

Say for example fuel temp is reading 80 degrees, very high but in range. At that temp lubricity of fuel is reduced, back flow is high, so ability to deliver high pressures is compromised. To mitigate, torque is reduced which should then lower work done by the pump, helping to reduce that high temp. This is not "limp mode".

I would expect there to be a plausability test on the fuel temp reading, usually after a prolonged engine off where you can expect all temps to be reading ambient. If that temp was still high, plausability test would fail and a fault would be logged. One reaction to that fault could be to apply a torque limit as it knows it could no longer trust the temp and has to assume worst case. That I could understand being called "limp mode" as it has recognised there is a fault that needs fixing.

You could get limitations if air flow was reading low. ECU knows fuel in, air in, so if A/F is low assumes you will be getting smokey, torque is limited as lower torque is less fuel and a higher A/F ratio, ie less smoke. Again not "limp mode". Low mass air flow happens if you're up a mountain, so in itself isn't inconceivable.

Again at some point there will be plausability tests on the air flow, but only if the flow is out of range would a fault be set and possibly a torque limitation applied.

That's just a couple of examples, there will be many more scenarios.

You need to find someone can look at the live data and understand what's happening. There are too many parts jockeys that rely on fault codes.

Note, iCarsoft isn't good for live data, Xentry is the best. I must stress the tool is an aid, it still needs someone that can diagnose driving it.

 

[rf065]

I read on here lots of talk of "limp mode" but no fault code. It is quite possible you have some failure that is causing a torque limitation without a fault, I would not call that "limp mode".

I would call limp mode when you are unable to rev above 3000rpm in any gear along with a lack of power. My CLK did this many times over a 2 year period without any fault codes or warning lights. Nothing to do with "torque limitation".