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Hi everyone! I’m having some issues with my transmission and was hoping I could get some help. My car is at 110,000 miles and I’ve been having jerky shifting between gears, especially when the transmission is cold, even if I’m not accelerating hard. I replaced the camshaft sensors as well as the crankshaft sensor to no avail. The transmission fluid was last changed around 91,000 miles, so I doubt the transmission fluid has crapped out but I’m gonna do a flush and clean the solenoids in the process. If it’s not having to do with the fluid being low or contaminated, would a likely possibility be that the transmission tcu could be malfunctioning? I’ve heard they can be problematic. I took my car to the mechanic and it pulled up the code P026E71 and it states that it’s regarding a coolant actuator valve malfunction. Could my transmission be overheating, therefore cooking the fluid, or could this be indicating a problem with the tcu. I only ask as Mercedes have been known to give inaccurate code readings. Im just spitballing and looking for some insight from more experienced people. Trying to avoid wasting more money than I have to on narrowing down the issue before it become irreversible.Attached I have the results from the obd scan. Thank you so much!
Has this been happening since before or after the last transmission oil change? It looks like they are using launch as diagnostics, did they try to activate that pump?
Auxiliary coolant pumps are known to go and their importance to good performance is underscored by modding to always on.
Has this been happening since before or after the last transmission oil change? It looks like they are using launch as diagnostics, did they try to activate that pump?
Auxiliary coolant pumps are known to go and their importance to good performance is underscored by modding to always on.
I purchased the car at 99,000 miles so only after the transmission fluid was changed so I cant say. I only noticed an issue around 105,000 miles. However the people that did the transmission fluid change, according to car fax it was a Mercedes dealer, thought it looks like they didn't replace the pan gasket and instead used gasket in a can, so my thought is that maybe some fluid could have leaked out. Relatively shoddy work that you wouldn't expect from a dealer, so my thought is if they were gonna cut a corner with replacing the gasket, they may have not done the fluid change properly either. Regarding the mechanic trying to activate the pump, they didn't however I could ask them to do so. If that were an issue, the auxiliary coolant pump is relatively cheap, would it be better to just replace it outright even as a preventative measure, or are you saying its an issue with electronics not properly communicating with the pump, so a new pump wouldn't solve the issue you're proposing? I can work my way around a cars mechanics without being a professional but the electronics is where my knowledge is limited, so my apologies.
I purchased the car at 99,000 miles so only after the transmission fluid was changed so I cant say. I only noticed an issue around 105,000 miles. However the people that did the transmission fluid change, according to car fax it was a Mercedes dealer, thought it looks like they didn't replace the pan gasket and instead used gasket in a can, so my thought is that maybe some fluid could have leaked out. Relatively shoddy work that you wouldn't expect from a dealer, so my thought is if they were gonna cut a corner with replacing the gasket, they may have not done the fluid change properly either. Regarding the mechanic trying to activate the pump, they didn't however I could ask them to do so. If that were an issue, the auxiliary coolant pump is relatively cheap, would it be better to just replace it outright even as a preventative measure, or are you saying its an issue with electronics not properly communicating with the pump, so a new pump wouldn't solve the issue you're proposing? I can work my way around a cars mechanics without being a professional but the electronics is where my knowledge is limited, so my apologies.
Honestly I cant say since all I have for maintenance records are the Carfax and they don't go into too much detail. I'll be flushing the torque converter along with transfer case when I change the transmission fluid. I was thinking of doing a throttle relearn, but isn't the throttle constantly learning? I've heard even without a reset, it usually will adapt to a new driver on its own after a few weeks of driving the car. I'm gonna flush the fluid, reset the TCM and update after.
I should add that the front differential went which is why I had it in the garage to begin with, so my thought is that if the TC wasn't flushed, it could be putting more stress on the diff and the transmission which could've led to its failure.
Honestly I cant say since all I have for maintenance records are the Carfax and they don't go into too much detail. I'll be flushing the torque converter along with transfer case when I change the transmission fluid. I was thinking of doing a throttle relearn, but isn't the throttle constantly learning? I've heard even without a reset, it usually will adapt to a new driver on its own after a few weeks of driving the car. I'm gonna flush the fluid, reset the TCM and update after.
Yes that sounds like a plan and worth as first troubleshooting steps.
I should add that the front differential went which is why I had it in the garage to begin with, so my thought is that if the TC wasn't flushed, it could be putting more stress on the diff and the transmission which could've led to its failure.
Although MB themselves don't have a maintenance schedule for the front differential, although they do for rear diff, the front one goes through a lot of stress holding the weight of engine and all the cornering manuevers, I really don't know why MB doesn't instruct on changing the fluid in the front differential.
the transmission fluid can absolutely go out in 20k. The regular drain and fill with the filter change leaves 2.5 quarts in there, the old fluid contaminates the new fluid so its a question of "how old is the oldest fluid in my transmission". And sometimes it just needs a second drain and fill to get the job done. I do a transmission service like once every 72hrs at the shop so I've seen them in all sorts of conditions. If you let it get bad enough it starts thinking sensors are going out lol
the transmission fluid can absolutely go out in 20k. The regular drain and fill with the filter change leaves 2.5 quarts in there, the old fluid contaminates the new fluid so its a question of "how old is the oldest fluid in my transmission". And sometimes it just needs a second drain and fill to get the job done. I do a transmission service like once every 72hrs at the shop so I've seen them in all sorts of conditions. If you let it get bad enough it starts thinking sensors are going out lol
yeah I can’t say the quality of the last flush so I’ll be doing it myself, cycling new fluid at least probably two times. The computer hasn’t stated sensors are going, I just have heard the crankshaft and camshaft sensors can cause jerky shifting, both of which usually seem to be problematic in my model, I just replaced them to try and narrow down the issue myself. I don’t think it’s not due to neglect on my end. Just trying to narrow down whether it’s a mechanical issue of some sort or if it could be an electrical issue with either the tcu or the computer on the valve cover.
yeah I can’t say the quality of the last flush so I’ll be doing it myself, cycling new fluid at least probably two times. The computer hasn’t stated sensors are going, I just have heard the crankshaft and camshaft sensors can cause jerky shifting, both of which usually seem to be problematic in my model, I just replaced them to try and narrow down the issue myself. I don’t think it’s not due to neglect on my end. Just trying to narrow down whether it’s a mechanical issue of some sort or if it could be an electrical issue with either the tcu or the computer on the valve cover.
Yup, sounds like a plan, hopefully the fluid change will fix it once and for all.
Yup, sounds like a plan, hopefully the fluid change will fix it once and for all.
emptied the transmission fluid and transfer case fluid. It looks brand new, no metal shavings and barely any metal on the magnet in the pan. I’m probably gonna clean the solenoids now but since the fluid being an issue is kind of ruled out, im not sure what the issue could be besides the fluid having possibly been low. I already changed the camshaft and crankshaft sensors so besides the solenoids or the tcu, im not sure what the issue could even be. On a cold start, the car will jerk heavily when shifting, especially from gears 2-3 and 4-5. Once the car is fully warmed up, it’ll still jerk just not as bad. Hopefully after the new fluids in it’ll change but I feel like it’s an electrical issue. I’ll have to find someone with a proper scanner to do the tcm reset, unless if the reset procedure you can do via holding the accelerator with the ignition on works but it didn’t change anything when I tried it last.
Last edited by egrey574; Apr 15, 2025 at 01:51 PM.
emptied the transmission fluid and transfer case fluid. It looks brand new, no metal shavings and barely any metal on the magnet in the pan. I’m probably gonna clean the solenoids now but since the fluid being an issue is kind of ruled out, im not sure what the issue could be besides the fluid having possibly been low. I already changed the camshaft and crankshaft sensors so besides the solenoids or the tcu, im not sure what the issue could even be. On a cold start, the car will jerk heavily when shifting, especially from gears 2-3 and 4-5. Once the car is fully warmed up, it’ll still jerk just not as bad. Hopefully after the new fluids in it’ll change but I feel like it’s an electrical issue. I’ll have to find someone with a proper scanner to do the tcm reset, unless if the reset procedure you can do via holding the accelerator with the ignition on works but it didn’t change anything when I tried it last.
Did you measure the amount was drained and confirmed if it was low or not?
Did you measure the amount was drained and confirmed if it was low or not?
I haven’t yet, we’ll see once I empty out the drain bucket. To add, the solenoids are spotless besides a bit of grey oil on the casing. The rest of my diagnosing is gonna have be after replacing. Also bought a replacement aux coolant pump but I’m not gonna have time get to it. The transmission fluid doesn’t smell burnt so I don’t think the blocked actuator caused it, but I’m still gonna be replacing it.
I haven’t yet, we’ll see once I empty out the drain bucket. To add, the solenoids are spotless besides a bit of grey oil on the casing. The rest of my diagnosing is gonna have be after replacing. Also bought a replacement aux coolant pump but I’m not gonna have time get to it. The transmission fluid doesn’t smell burnt so I don’t think the blocked actuator caused it, but I’m still gonna be replacing it.
Its been a couple weeks since I finalized all repairs, I replaced all drivetrain fluid, removed the valve body (Broke the plastic valve body selector rod in the process, no tutorials I saw mentioned needing to have it aligned properly when reinstalling the valve body)and cleaned it along with the solenoids, replaced the auxiliary coolant pump and did a TCM reset (Manually, not with a bidirectional scan tool) It seems to shift slightly better? I noticed since that it mainly happens when accelerating lightly, when I go heavier on the gas the shifting seems to be much smoother. Honestly since the fluid was clean and the solenoids had no buildup, I'm not sure I did much to solve the issue besides narrowing down that likely it wasn't mechanical, however the aux pump needed replacing anyway. I think the transmission fluid may have been slightly low, but I think that was only part of the problem, there's no more hard jolting but there's still a noticeable bump when shifting occasionally, especially from gears 4-5. I've heard from some the shifting just sucks on 7Gtronic transmissions but I've heard from others it should always be "buttery smooth" and I don't have enough experience driving Mercedes to know honestly. I feel as though it may be an issue with the TCM, if there even is an issue at this point, but until my car starts throwing codes, I'm just gonna deal with it. I'll just leave this as a resource to maybe lessen trial and error in anyone in the future that runs into the same issue.
Its been a couple weeks since I finalized all repairs, I replaced all drivetrain fluid, removed the valve body (Broke the plastic valve body selector rod in the process, no tutorials I saw mentioned needing to have it aligned properly when reinstalling the valve body)and cleaned it along with the solenoids, replaced the auxiliary coolant pump and did a TCM reset (Manually, not with a bidirectional scan tool) It seems to shift slightly better? I noticed since that it mainly happens when accelerating lightly, when I go heavier on the gas the shifting seems to be much smoother. Honestly since the fluid was clean and the solenoids had no buildup, I'm not sure I did much to solve the issue besides narrowing down that likely it wasn't mechanical, however the aux pump needed replacing anyway. I think the transmission fluid may have been slightly low, but I think that was only part of the problem, there's no more hard jolting but there's still a noticeable bump when shifting occasionally, especially from gears 4-5. I've heard from some the shifting just sucks on 7Gtronic transmissions but I've heard from others it should always be "buttery smooth" and I don't have enough experience driving Mercedes to know honestly. I feel as though it may be an issue with the TCM, if there even is an issue at this point, but until my car starts throwing codes, I'm just gonna deal with it. I'll just leave this as a resource to maybe lessen trial and error in anyone in the future that runs into the same issue.
Ya the shifting of the 7G is a YMMV thing when new. Sounds like you got most of it corrected though.
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