Hello Scotty, thank you for sharing your car knowledge with us. I have a Mercedes-Benz C320 made in 2000 that has difficulty shifting into the 2nd gear and onwards. It is a 5-speed automatic transmission and has about 300,000 miles.
The problem occurs mostly in the morning. I have to park and turn off the engine, wait a bit and then restart the engine before it can shift into the second gear again. I do this about 4 times in the morning before getting to work. I noticed that it improves as I drive. I mean it shifts properly into the next gear without problems. When I drive back home, the shifting is a lot better. Sometimes though, when I stop at a traffic light, it becomes sluggish to even move when the light turns green. But if I sustain the acceleration, it will move faster after 3 seconds.
My theory is the transmission fluid is low or too viscous. Some mechanic checked it and found it to be at the appropriate level but the engine was not running while he did it. I would like to be really educated on this issue. Any recommendations would be welcome.
Thank you so much Scotty. Looking forward to your response.
Is the transmission in normal or limp mode? The symptoms you are describing are very similar to the transmission switching into limp home mode. You can tell when the limp mode engages by looking at your dashboard: if the gear indicator shows "D" when "D" is engaged, it is normal mode; if it is just lit - it is limp mode.
The limp mode can have a ton of reasons - from brake light switch failing to condensation in the shifting gear electronics. I guess you will need to get a scanner attached and base further investigations on what errors your transmission has generated.
Thank you for your response @dontknowler. My dashboard doesn't show gear indicator but I have noticed the odometer goes to 0 once it fails to shift. Does this count?
If we should start guessing, I would suppose that both the odometer and the gearbox need some sort of a speed signal input to work properly. As soon as this signal vanishes - for whatever reason this may be, both the odometer and the gearbox would stop working properly. For the gearbox it would mean that it would engage the limp home mode with gear 1 (or only gear 2, for cars with low gear for all-terrain use) accessible. Another way you can know that this limp mode is engaged; if you do not have a dashboard indicator: you should be unable to move the gearbox selector from "D" to "P" or "R" without turning the engine off first.
My sincerest recommendation would be to just attach a scanner and read the codes. In many cases the Mercedes Benz software is clever enough to give you a fairly specific code which would be enough for troubleshooting success. If you dont have a scanner, just buy one: Scotty had several videos on what scanner(s) to choose. The scanner pays for itself soon enough.
Thank you. Once it happens, I am able to put it in P without turning off the engine.
I am definitely getting it scanned to see the error. Thank you very much for your help.
Another not-so-obvious possible problem cause, out of my own long experience:
there are two ATF lines interconnecting the gearbox and the radiator. These lines are partially metal tubes and partially flexible hoses. Due to old age the compression fittings which interconnect the tubing and the hoses tend to leak. Even the smallest amounts of air which got inside the pipes / hoses overnights at those leakage points were in my case enough to cause gearbox malfunctions upon startup, obviously as those bubbles reached the valves and the associated labirynth of channels inside the gearbox. There were kicks when shifting, or severre shifting delays, or even failures to shift. As I drove during the day, these bubbles got slowly flushed out of the system, so over the day the gearbox functionality improved. And after each next night the problem returned.
Workshops recommended upfront valves module replacement, which was $$$.
But by taping up the leakage points at the abovementioned lines I figured out that they were the lines and not this module who were at fault. The long-term fix was an easy one: instead of even getting those lines replaced, I added some of the leakage-stopping additives Scotty had recommended (ATP AT-205) to my ATF fluid, and the lines leaks stopped magically, and I never had those shifting problems again ever since, although 4 years have passed.
So just have a look at all those compression fittings along the ATF lines: if there`s moisture, this could be the case or one of the cases for your gearbox problems.
Thank you @dontknowler. I'll definitely keep this mind and do the inspection myself to what extent I can. This is a cause that didn't even cross my mind. Come to think of it, we had an issue recently where engine oil was mixing with coolant fluid. Most mechanics recommended a new engine until one of them figured out a hack to prevent the mixing. I believe the transmission issues started afterwards. Maybe they're related?
" we had an issue recently where engine oil was mixing with coolant fluid ... the transmission issues started afterwards"
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Luckily I have no personal experience with oil and coolant mixing together. I can only confirm that this sounds like a severe engine-internal problem ranging from a blowing headgasket to cracks in the engine head or block. I can also confirm that in some rare and lucky cases you can get rid of this problem, at least temporarily, by using hacks like headgasket sealants added to your engine oil.
Unless - unless it is just a leak in the oil-and-coolant heat exchanger. In Mercedes cars those are poorly built and tend to have oil leaks to the oitside, especially during cold weather, and this is a widely known issue I also used to have; however in rare cases those leaks can be exchanger-internal too, and in the latter case the result could be oil and coolant mixing together. This heat exchanger is inexpensive and not hard to replace even in DIY mode. Newer versions of this part are much better made than OEM ones.
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This coolant-in-engine oil problem however sounds very engine-internal, and I have no idea how this could have affected your gearbox.
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However unluckily for me I have excessive experience with coolant getting into my automatic gearbox = automatic transmission fluid = ATF. I had this issue on my 30 yo Audi, however my w163 is technically prone to such issues as well, just as any other car with an integrated ATF-and-coolant radiator is. In most such radiators, only two tiny O-rings separate the coolant and the ATF circuit. Those O-rings are non-replaceable and are hidden deep inside the radiator internals, and once they lose elasticity (and with age they tend to do so), your coolant will start getting into your ATF. You can easily tell that your ATF has coolant within, because in this case it gets a very specific look - I hope "foamy" is the right word for it: with many tiny air bubbles within. Also, the ATF level starts to increase (cause the inflowing coolant volume adds up to the ATF volume). It is hard not to notice foam in the coolant visually, neither is it possible not to notice this when you drive cause this comes with heavy slippage of the friction disks when switching "upwards". But I did not mention this scenario earlier cause you wrote that you had your ATF level (although incorrectly) checked by a mechanic, and even a bad mechanic would have noticed that an ATF is foamy. So I hope this is not your scenario. Cause if it is, it is often the end of your transmission: the friction disks within the automatic gearbox consist of some sort of cardboard-like material, which is very friction-resistant when operated in ATF, but which would fall apart almost instantaneously when operated in contact with water, coolant or similar other non-oily liquids. Particles which get into the ATF as your friction disks start to degrade rapidly due to the latter getting in contact with coolant are also impossible not to notice in the ATF when doing any level checks.
"Some mechanic checked it and found it to be at the appropriate level but the engine was not running while he did it"
Dont go to this mechanic any more. You dont check your ATF level with your engine off. It is a very specific procedure how this check shall be done, and if you are not sure how to - just take your time to google. It must be described somewhere on the internet in full detail. At least I had no issues finding a description for my w163.
Yes, that was a serious red flag. I'll have to get the dipstick and do it myself at this point.
https://www.mercedesmedic.com/reset-mercedes-benz-transmission-procedure-instructions/
Here is a link to Mercedes medic about resetting transmission and how.
First reset the transmission. Turn everything off , radio, headlights ect. Turn key to second position and press pedal all the way down and hold it for at least 10 seconds. Then turn key to off position while still holding pedal down. Release pedal and wait around 2 minutes. Keep key in ignition .Transmission control module has now been reset. Drive normal and take a easy. Driving fast will cause shift points to be higher.. if it doesn't work do the same process but remove key at end. If it still doesn't help that most likely is not your problem.
It's possible your solenoids are bad or the conductor plate. Sometimes the adaptor will leak and fluid gets sucked through the wiring harness and into the control module itself. That can cause a whole host of issues on its own.
Always check fluid with car at full operating temp. If the transmission isn't at temp and you check the fluid level it will be inaccurate.
Another possibility is the transmission has coolant in it. The cooler will break in radiator and the fluids will start to mix. I can't remember off hand if this was a issue in your car or year.
I'll do this and give you the feedback on the outcome. Thank you @Nissanrob88
I forgot to add not to touch any buttons or turn anything on or off when doing this. Also don't open doors or close doors . You want everything off and untouched when doing it other wise it may not work. You will know if it works once you start driving it. Alot of people say it feels like a new car after resetting especially if you never reset it before. A Mercedes bulletins says it should be done once a monthly.
Resetting adaptation on an old transmission is an extremely dangerous thing to do, hence it is smth I would not recommend doing unless absolutely necessary. The reason is that part of this adaptation is an adjustment which lets the gearbox "know", when doing shifting, that old friction disks have a significantly lower thickness than they used to have when they were new.
And here comes the problem: immediately after adaptation reset, the gearbox starts opertating old disks as if they were new. Of course it soon notices that old disks react differently, and initiates the re-adaptation procedure. However this procedure comes with a certain "learning curve". And on old transmissions the gearbox ECU very often manages to ruin the old friction disks by improperly operating them, hence to ruin the entire transmission, way before this re-adaptation is complete.
So be warned.
Resetting the adaptive transmission to factory settings isn't dangerous or harmful. It's a standard process that is recommended and frequently done by all dealerships and German car specialist and Mercedes owners alike. The manufacturer tells you to reset it frequently for best performance and gas mileage..it's obviously you have no idea how transmissions work or anything about adaptive transmissions. The clutches are being used the same no matter what. It doesn't matter if it's by a reset or learning while driving. Resetting the transmission won't have anything effect on them. Remember it's called adaptive meaning it's always learning. You just driving slow for a minutes will reset the shift points to a lower rpm to match that driving style. Same goes if your accelerate heavily. Car will learn that and shift at high rpms. The transmission learning that is no different then a factory reset. So by your logic he can never drive the car again .
"it's obviously you have no idea how transmissions work or anything about adaptive transmissions"
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My information comes from a professional ZF service doing automatic transmission rebuilds for ages. They are THE best specialists in this field I am aware of in this whole world. And they dedicated a whole video to explaining why you should never reset adaptation on old transmissions. Here is the link, and if you are really interested, have smb translate the video for you - you will definitely find out that your current understanding of how automatic transmission adaptations work is, mmm, very limited. (
). On-the-fly adaptiation of shiftpoints to rpms to match smb´s driving style mentioned by you has nothing to do with background adaptation processes which happen in the automatic transmission electronics and which have to do with residual friction disks thickness. And which also get reset as you do the general at adaptations reset.