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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 27918
Experience:  Over 15 years experience as a Mercedes dealer technician
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SL 550: Have a 2009 Mercedes SL550. When driving in S or C

Customer Question

Have a 2009 Mercedes SL550. When driving in S or C mode in Drive the car will automatically kick down into lower gears even though the car is in drive. If at hiway speeds it can kick down to 3rd or 4th, if in town it can kick down to 2nd or first.
You can clear the issue by going into neutral and popping it back into drive. Any ideas?
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 you have no check engine light on with this issue here this can be due to a fault with the shift adaptations being off.What needs to be done from here is to have a scan tool/computer or dealers SDS machine plugged into your model to relearn the shift adaptations.Once this is done this should correct the shift points as well as the down shift points correcting this here.Most shops or a dealer will usually charge about an hours labor to relearn the shift adaptations to correct this fault here.This does need done as well as having the fault codes checked with the same machine plugged into your model to locate any codes set that may help diagnose and shift issues but I suspect the shift adaptations need relearned to correct this fault here. 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.
Sorry for the delay getting back to you.I took it into Kennewick Mercedes and they did hook it up to the computer to reset the shift adaptions. They told me the car is not trowing any codes at all. No more then a mile from the dealership it did it again.So while the car is in either COMFORT or SPORT this can happen. I cannot detect a common them or condition that makes it downshift from DRIVE, it just sometimes does it.Tonight a was cruising at about 40mph and the car downshifted to 3rd gear. The instrument cluster still showed the car in SPORT mode but instead of seeing "D" it showed "3". As third gear slowed the car way down it then down shift to 2nd before I kicked it into NEUTRAL and back into DRIVE, this clears the symptom.So, not check engine light, no codes, and reset the adaptive transmission. Any ideas on what to do from here are appreciated.Thanks Pete