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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 27862
Experience:  Over 15 years experience as a Mercedes dealer technician
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08 s550 4matic while driving RPM go way up to 7 on

Customer Question

08 s550 4matic while driving RPM go way up to 7 on tachometer,car stalls it happens maybe 2 or3 times a month had it check at dealer found no problems need help to see what's going on
Submitted: 1 year ago.
Category: Mercedes
Expert:  Pete replied 1 year ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

If the engine isn't actually revving up this high but the tach itself says it is and the stall out occurs this can be caused by a faulty crank sensor itself.It is the sensor that determines the engine rpm and when it acts up it can cause false signal readings like this here as well as a stall out in some cases.If this has not been checked or replaced already I suspect this is the cause needing replaced.If the engine is revving up this high then stalling out let me know so we can continue.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.Thanks Pete.

Customer: replied 1 year ago.
Hi Pete, Yes, the engine is revving up. The vehicle was taken to the Mercedes dealership a few weeks ago and they could not find anything, however, this issue has occurred again since it was taken to the dealership. I was merging onto the interstate and the engine revved up and the rpm went up to the 5 mark. The vehicle felt as if it was resisting going any faster (almost as if I either had the car in the wrong gear or had the emergency break on...however, neither of these cases existed). It does not happen every time that it is driven, which makes things more confusing.
Expert:  Pete replied 1 year ago.

Usually this is caused by a fault with the transmission valve body that will cause this fault here or an issue with a solenoid on the valve body.I have seen both of these occur needing to have the affected component replaced to correct this.Most common is usually the valve body itself.

The only other component that I see that may cause this is a fault with the engine computer itself.I have seen some of these fail before and not set a fault code for itself failing making it difficult to diagnose properly.

The only way to be sure of which is the component at fault here this would need checked/tested when the vehicle is acting up.Unfortunately I have had to ask my customers to see if they can leave their vehicle with me for a day or more for further diagnosing to see if I can pinpoint the fault when the issue occurs.

Thanks Pete

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