roadventure

I own a 2015 E350 4matic Sport Wagon. It currently has 102,200 miles on the odometer. About three weeks ago the "check engine" light came on and the car wen into what I will describe as "limp mode". It became very sluggish and seemed to be not running on all cylinders. I pulled into a parking lot after about 1/4 mile and shut the car off. After 2 minutes I started back up and the "check engine " light was off and again running normally. This happened three other times in the following weeks.

I set up a service appointment at my "local" (about 50 miles) Mercedes dealer. They hooked the car up to diagnostics and did not find any codes stored. I had planned to have a lot of services performed: cooling system flush, brake fluid flush, trans service, spark plug change, replace battery, steering rack recall, oil seepage at front valve covers and the B-Service.

Being as there were no codes and the no record of the spark plugs having ever been changed, the technician stated that the engine may have been missing due to worn out spark plugs. It seemed reasonable to me at over 100,000 miles potentially on the original plugs.

The work was done over two days and I went to pick up my car. Driving home was fine, no problems. The next day, I drove to the P.O., about two miles one way and on the trip back the check engine light comes on again and the car goes into what feels like "limp mode" again!

WHAT do you all think should be looked at IF there are STILL no codes recorded in the computer on this car?

Thanks for any and all help in advance.

dave

juanmor40

You say the car is 100K+ miles, and behind the spark plugs service due @60K ? Careful those get seized on the threads next time around.

Can you correlate fuel tank level with the failure? Fuel rail pressure starting to fail? Fuel filter at the pump starting to fail?

probably more info needed. I would try correlate when it happens to something in the car. How are your batteries?

Arrie

One reason limp mode sets ON is low fuel rail pressure. Could be faulty pressure sensor or fuel pressure really is low.

Next time it happens drive to MB or other service with scanner without re-starting if you are not too far from such a place to limp to. Most car part stores scan for CEL and perhaps can see what the code is if the light is still ON.

Don’t let them stop the engine before connecting scanner as this will obviously clear the code. Some scanners say to connect with car power OFF but this is nonsense. I always start my cars first before connecting the scanner. So does the place that does my state inspections.

Does the limp mode come on easily if you step on the gas fast? This would be a sure sign of fuel pressure problem.

juanmor40

Since you mentioned your closest MB dealer is @50miles, I think a good ODB scanner, relatively compact would be a great investment to have either in the glove compartment, or the rear left trunk compartment. You can then scan on the demand anywhere as @Arrie suggested

I use iCarsoft, but others can comment on their preferences

roadventure

Thanks! My nearest MB dealer is 50+ miles away, so not knowing if the problem could cause damage from additional driving, maybe not the best, first choice. BUT, the idea of trying a scan at a local generic parts store (AutoZone, Quest Auto, etc.) is a good idea.

It seems to me that a code could be cleared by simply turning the car off seems to be a ridiculous design. What possible down side could there be to recording every event each time it happens? Memory space, in this day and age, could not possibly be an issue.

Yes, the car does seem to NOT gain power when stepping on the gas pedal when this is happening.

Good ideas! Thanks.

dave

juanmor40

Dave, I think Arrie meant that if you suddenly step on the gas, the ECU realize there is not enough fuel pressure and it gets into limp mode, and triggers the CEL.

While coasting, step heavy on the gas and see if it reproduce the problem

roadventure

Agreed, I was not clear in my writing. Yes, when I suddenly step on the gas it can be put in the "limp mode" and turn on the check-engine light. I also had it happen when going up an incline when driving to the dealer for the initial service I described previously. There are very few elevation changes in my area being at about 10 to 20 feet above sea level. But, when approaching a bridge (going up a hill) the check engine light did come on and the performance got crappy.

I am getting the feeling that fuel supply may be the, if not part of the problem.

My car has 100,200(+) miles on it. As far as I know any fuel filters are the originals. I know on less complicated cars (my 69 AMX for example) when the fuel filter is not flowing well I will get very poor performance. In that condition when I step on the gas the car slows down...

dave

CaliBenzDriver

I think your limp-mode under acceleration is a prime case of a mad computer gang.

You said your main battery just got replaced so we can assume it's out of question. Do you know about how old was the previous one?

​​​​​​The ECU and Tranny controllers in these cars are some of the most sofisticated modules available from Bosh, Siemens, Continental... They do include automatic FAULT journaling.... I can hardly believe your limp-mode faults not being recorded but when soft-crash strike, everything may be possible.

It's safe to say one of your modules is ruining your car reliability. You need to retrieve your car DTC's on regular basis to help figure things out.

roadventure

What is a "DTC"?
dave

konigstiger

Diagnostic Trouble Code, stored/current fault codes.

S-Prihadi

DTC = Diagnostic Engine Troublecode. These are numbers produced for reporting by engine computer to what are the problem/s...maynot be accurate 100% yah, DO BE CAREFUL.

Check engine light showing and even though it goes away on its own, will create a STORED event. Not Current but STORED.
Check Engine Light to be shown on dashboard is quite a level of threshold exceeded.

When they replaced the spark plugs, which cylinder has the ugliest black soot ?
Any good photo of the old removed spark plugs ?

Arrie

YES, that is what I mean.

Arrie

Well, you likely have a fuel rail pressure problem or fuel rail pressure sensor problem. I understand that a 2015 model has the direct injection engine so there are low pressure "delivery" pump in the gas tank and then the high pressure fuel pump under the hood at the start of the fuel rail close to the fire wall. In my understanding there is no pressure regulator or return flow from the rail as with non-direct injection systems. The pump takes care of regulating the pressure based on the pressure reading by the sensor so the issue can be either the sensor or the pressure really gets low when you step on the gas pedal.

And there is no danger to the engine driving in limp mode (other than someone from behind rolling over your whole car when it happens), it just is very poor performance of the engine...

roadventure

Good point. What model iCarsoft scanner have you been using?

konigstiger

More than likely they checked but you never know given dealer performance of late. Found this Service Campaign that may apply if applicable should have been listed in Vehicle Master Inquiry (VMI), requires ECU software update.

roadventure

Thanks. I got this from another forum and took it to the dealer with me. They claimed that it was not the issue even though, at that time, I was not able to present the car with the check-engine light ON.

The check-engine light is now ON consistently, every time I drive, so they will be able to see what made it come on and correct it, hopefully. Will be going back to the dealer in a few days.

roadventure

Thought I would bring closure to this thread with a report on what finally needed to be repaired. I picked up my car from the dealer yesterday after leaving it with them to check for codes and, hopefully, repair what was broken.

After emptying a bottle of Chevron TECHRON Fuel System Cleaner into the fuel tank the check engine light came on again, as it had been doing lately, but this time it stayed on. I have no idea if the TECHRON application had anything to do with anything. So, I dropped the car off to the dealer again since now they had something they could get from the computers.

What they came up with was:

Diagnostics found code P030485. #4 cylinder misfire (front, left-hand cylinder). Compression test on #4 slightly higher than spec. No fuel injector leakage found. No air intake leaks. Suspect intermittent faulty ignition coil.

So, they replaced the #4 cylinder ignition coil and we shall see. But, based on the initial performance problems, I think this may have been the problem.

S-Prihadi

A misfire if so obvious combustion wise, the spark plug color can not lie.
2nd time I am asking :

20 Dec 2021:
When they replaced the spark plugs, which cylinder has the ugliest black soot ?
Any good photo of the old removed spark plugs ?

We as car owners must be more critical looking at the evidence of the claimed failure of the component.

01. Did dealer tech did the usual confirmation by swapping coil and plug to and with another known good cylinder and see if misfire follows the coil + plug ? If this is done, it is proper troubleshooting.
If dealer tech blindly follows only what Xentry reported....hhhmm, not good.

02. If swapping coil & plug resulted same cylinder 4 as problem, this will get interesting.

I hope all good with your engine yah.

chassis

Techron was a waste of money, a scam. Unfortunately.

1. Replace the main battery and aux battery/capacitor. You have a 7 year old car and this is good practice. Batteries start to give up the ghost around 4-5 years.

2. Check the engine harness for signs of oil: pull apart cam position sensor connectors and cam magnet connectors. If oil is present you have found your problem.

3. You need to catch up on all maintenance. This avoids confusing and complicating a problem you are experiencing with multiple potential causes. Going through this process will give you or your mechanic a good feel for the car. Replace transmission fluid, replace brake fluid, replace engine and cabin air filters, clean and lubricate all rubber gaskets (doors, hood, tailgate, sunroof).

Give the car a good going over. Get it up to snuff.

roadventure

Agreed. As of December 2021.... Coolant flush/replace; brake fluid flush/replace; engine oil & filter replaced, transmission fluid replaced; engine & cabin air filters replaced; front sway bar links replaced; sunroof & shade rails cleaned & lubricated; all rubber seals at doors cleaned & treated; Main battery replaced (aux battery to be replaced soon).

Overall maintenance history is pretty good on car based on Carfax report. It was lacking somewhat from 75-90K miles (I bought the car at 90,300 miles) but anything missed during that time has been brought up to current. At this point I am confident that it can continue on with the recommended schedule set by Mercedes with few surprises.

roadventure

Sadly, for me, I did not request that the old plugs get returned to me with labels as to the position they came from. My mistake. So I can't speak to the condition of the plugs.
01. the tech DID swap coils, inspect plugs (new as of 12/18/21) and check continuity of wiring related to coils.

02. Coil #4 was tested and did exhibit inconsistency.

My car runs great now and I am very happy to have it back. They gave me a 2021 GLC 300 4Matic for a loaner. I DID NOT like it at all. The transmission seemed to be almost constantly shifting and just felt under powered.