W212 transmission shift
08-10-2021, 04:36 AM
#26
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pierrejoliat (04-07-2022)
04-06-2022, 04:27 AM
#27
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Mercedes E350
I have a W212 which I have been using since the past 3 years and have been very happy about the performance. It's a 2012 model. Lately it has been having a problem where the Transmission does not shift normally while using the AC. With the AC turned off, the transmission shifts flawlessly and smooth at 1500RPM from the 1st gear upwards and feels just about right as I have always been using it. But lately with the AC turned On, it feels like the car has to force itself to change from the 1st to the 2nd and 2nd to the 3rd gear and so on till the RPM reaches around 2200. On a normal traffic day, it gets very annoying as the car is mostly stuck up at the 2nd gear most of the time and I really have to speed up quite a bit to force itself to change the gear up. On turning off the AC, the problem immediately goes away and the transmission is smooth and flawless. Have even tried doing a transmission reset by turning the key to position 2 and pressing the gas pedal all the way down for like 30 secs and then the rest of the procedure but to no avail. Any suggestions would be very helpful.
I would like to ask you if you have found a solution to your problem? I'm having the same problem and I haven't found a solution.
08-19-2022, 07:24 PM
#28
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OK, so I've been told a few things related to this. Firstly, the MB transmission cooling depends on the speed, rpm, of the input shaft - this is because the pump is driven by that shaft and it is the pump that circulates the fluid through the radiator. So for a given vehicle speed operating the transmission in a low gear improves the cooling. This effect is most noticeable with the larger engines as they tend to spin the transmission input slower as they have more torque. When the smarts see the AC is on the system becomes even more conservative about cooling the transmission and switches to lower gears earlier. Having said the above this doesn't mean that you don't have a bad sensor, telling the transmission is hotter than it really is, or that indeed your shifts are rougher than they should be but I think the logic behind raising the RPM to change up is expected.
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
Peter
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
Peter
Last edited by T100T; 08-20-2022 at 05:46 PM.
03-30-2024, 11:27 AM
#29
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E220 CDI W212
AC On RPM higher for Initial 1-2 KMs in Summer
OK, so I've been told a few things related to this. Firstly, the MB transmission cooling depends on the speed, rpm, of the input shaft - this is because the pump is driven by that shaft and it is the pump that circulates the fluid through the radiator. So for a given vehicle speed operating the transmission in a low gear improves the cooling. This effect is most noticeable with the larger engines as they tend to spin the transmission input slower as they have more torque. When the smarts see the AC is on the system becomes even more conservative about cooling the transmission and switches to lower gears earlier. Having said the above this doesn't mean that you don't have a bad sensor, telling the transmission is hotter than it really is, or that indeed your shifts are rougher than they should be but I think the logic behind raising the RPM to change up is expected.
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
Peter
For me, E550 in Houston, in the morning it will shift normally and in the late afternoon on the way home it will delay shifts until I've gone a few miles, it seems the programmers at MB made this very conservative (or I too have an issue) as I can't imagine the transmission hasn't cooled well below operating temperatures after being stood for 8+ hours.
Peter
04-01-2024, 05:52 AM
#30
I am facing the same issue with my W212 CDI which is a 2012 Model. The issue comes at the start if the AC is switched on. Also noticed in the summer when outside temp is about 32Degree C. The issue comes in the initial 1st few KMs that the RPM shifts gears at around 2200 - 2400 RPM as against 1800 - 2000 RPM (with AC off). The interesting thing in common (as mentioned in the thread above) is that after driving a few KMs (~ 1-2 KM) with the AC on, things get back to normal for the Transmission and it shifts normally at 1800 to 2000 RPM. So noticeably this issue is coming in the extreme summer temps, however would like to know from the forum if something needs to be checked as I am also a person, like all enthusiasts here, who would need to know if something needs to be checked/corrected on the car.
As picture I've take, This is 2 delayed poitswitch - that mean delay shift for max cooling on summer and for heating in cool wheather.
And yes, you can disable it via coding. Try Vediamo or some reader can code your HAVC. Good luck.
