Hey folks! I'm looking for some wisdom on my transmission. Any guesses about how to solve this problem would be much appreciated. Fortunately I can live with it, but I’d like to fix it.
In brief, transmission won’t upshift if car has sat in dampness for a long time. Problem disappears when warmed up and driven a few miles. It will start in 2nd if the switch is set to “W.” Transmission otherwise works fine. As described below, transmission is in mechanically good shape, had fluid changed at 73K mi, and has zero sign of abuse. Photos below show codes.
Detailed Background:
1999 C280 Sport, purchased in Vallejo, east of San Francisco in June 2017 with 73K miles and in overall excellent condition. Shortly after purchase, I did a complete transmission fluid change (including torque converter) and replaced filter, pan gasket, electrical plug, etc. Car ran perfectly before and after. Used fluid was a normal pinkish color, no burned smell, normal amount of clutch residue in pan, no metal flakes or “sparklies;” everything basically normal. Prior owner was a very conservative driver (older guy), who probably never once floored the accelerator. When I test drove the car, he marveled when I used the shifter lever and said that all he ever used was “R” and “D.” I’m 3rd owner of the car and a former mechanic. (In the 1980's.)
Details on Current Problem
For the first 20K miles or so after purchase, the car performed excellently. In fact, the more I drove it, the better it got. I spent many weekends driving between Redding California and San Francisco, a roughly 450 mile round trip through the often-hot Sacramento Valley. Car was happy cruising at 85MPH, and happy negotiating traffic, hills, and stop-and-go in San Francisco. In short, an excellent performer.
In January 2019, I left the car for a couple of months at a friend’s house in San José, CA. Unusually, this was a very rainy period. When I got back, the car wouldn’t upshift. Since I had had the car for two years, and didn’t know the vintage of the battery, I replaced it with a fresh MBZ battery purchased at the dealer. This did not help. Since the car ran fine except for lacking upshifts, I contemplated driving slowly back to where I was living in Redding by using the “W” setting on the transmission and limping along in second gear the entire way. But I first decided to drive it around San José a bit, and took it to an independent MBZ mechanic. (Normally I do my own work, but was far from my tools.) They said they didn’t work on transmissions, but would be happy to read the codes for me. (No CEL light was on.) The codes were inconclusive, though they seemed to indicate some kind of communication problem between the shift lever and the transmission. See the photos of the Star Diagnostic printout below.
After I left the MBZ mechanic with a recommendation for an MBZ transmission shop, I headed back to my friend’s house. Within five minutes, the transmission started to function normally again. I drove the car around the Bay Area for a couple of days just to be sure, and it continued to work just fine, so I drove back to Redding. After that the problem vanished for most of a year.
A year later, I drove the car back to my home in Boston. There, after sitting for six weeks, the problem returned. But once I had driven the car around for a while and gotten the engine and cabin warmed up, the problem vanished again.
So the problem seems to be caused by dampness and/or disuse. If I drive the car regularly, there’s no problem, even if temperatures are well below freezing. But if it sits in a damp place for a week or more, then the problem returns. Unfortunately, Boston is the very definition of a damp place, and my cars often sit for weeks or months while I travel. I just came back from a 23 day trip, tested the car, and the problem was back, but disappeared after I let the car idle in the driveway for about 12 minutes and then took a 1-mile drive. Oh, and it initially didn’t engage first until I had revved the engine a bit, and then engaged with a thunk or jerk.
Preliminary conclusions:
Get codes cleared (I’m not sure if last mechanic did this; they didn’t charge me for a half hour of work), and then try to recreate problem and read codes again.
Maybe replace shift position sensor; depends somewhat on what you all have to say. Otherwise, I'm at a bit of a loss. And as noted, the problem is annoying, but not really keeping me from using the car, especially once it's back in more regular use.
Attached are photos of the codes from the Star Diagnostic system that the mechanic kindly gave me.
Thanks for reading and have a great day!
![2618654]()
![2618655]()
![2618656]()
![2618657]()
In brief, transmission won’t upshift if car has sat in dampness for a long time. Problem disappears when warmed up and driven a few miles. It will start in 2nd if the switch is set to “W.” Transmission otherwise works fine. As described below, transmission is in mechanically good shape, had fluid changed at 73K mi, and has zero sign of abuse. Photos below show codes.
Detailed Background:
1999 C280 Sport, purchased in Vallejo, east of San Francisco in June 2017 with 73K miles and in overall excellent condition. Shortly after purchase, I did a complete transmission fluid change (including torque converter) and replaced filter, pan gasket, electrical plug, etc. Car ran perfectly before and after. Used fluid was a normal pinkish color, no burned smell, normal amount of clutch residue in pan, no metal flakes or “sparklies;” everything basically normal. Prior owner was a very conservative driver (older guy), who probably never once floored the accelerator. When I test drove the car, he marveled when I used the shifter lever and said that all he ever used was “R” and “D.” I’m 3rd owner of the car and a former mechanic. (In the 1980's.)
Details on Current Problem
For the first 20K miles or so after purchase, the car performed excellently. In fact, the more I drove it, the better it got. I spent many weekends driving between Redding California and San Francisco, a roughly 450 mile round trip through the often-hot Sacramento Valley. Car was happy cruising at 85MPH, and happy negotiating traffic, hills, and stop-and-go in San Francisco. In short, an excellent performer.
In January 2019, I left the car for a couple of months at a friend’s house in San José, CA. Unusually, this was a very rainy period. When I got back, the car wouldn’t upshift. Since I had had the car for two years, and didn’t know the vintage of the battery, I replaced it with a fresh MBZ battery purchased at the dealer. This did not help. Since the car ran fine except for lacking upshifts, I contemplated driving slowly back to where I was living in Redding by using the “W” setting on the transmission and limping along in second gear the entire way. But I first decided to drive it around San José a bit, and took it to an independent MBZ mechanic. (Normally I do my own work, but was far from my tools.) They said they didn’t work on transmissions, but would be happy to read the codes for me. (No CEL light was on.) The codes were inconclusive, though they seemed to indicate some kind of communication problem between the shift lever and the transmission. See the photos of the Star Diagnostic printout below.
After I left the MBZ mechanic with a recommendation for an MBZ transmission shop, I headed back to my friend’s house. Within five minutes, the transmission started to function normally again. I drove the car around the Bay Area for a couple of days just to be sure, and it continued to work just fine, so I drove back to Redding. After that the problem vanished for most of a year.
A year later, I drove the car back to my home in Boston. There, after sitting for six weeks, the problem returned. But once I had driven the car around for a while and gotten the engine and cabin warmed up, the problem vanished again.
So the problem seems to be caused by dampness and/or disuse. If I drive the car regularly, there’s no problem, even if temperatures are well below freezing. But if it sits in a damp place for a week or more, then the problem returns. Unfortunately, Boston is the very definition of a damp place, and my cars often sit for weeks or months while I travel. I just came back from a 23 day trip, tested the car, and the problem was back, but disappeared after I let the car idle in the driveway for about 12 minutes and then took a 1-mile drive. Oh, and it initially didn’t engage first until I had revved the engine a bit, and then engaged with a thunk or jerk.
Preliminary conclusions:
- There’s almost certainly nothing wrong with the mechanicals of the transmission. When it works, it works great, no slipping, no hesitation to downshift, etc. I’m willing to hear otherwise, but this is my preliminary working conclusion. That said, the springs in the valve body are notorious for breaking. Maybe one of those is broken? I’ve looked into the Sonnax kit, and will likely do this soon as I’ve now got 30K on the “new” transmission fluid, and it's due to be replaced once more. While I've got the transmission pan off, it would be criminal to not at least look at the springs in the valve body. Counter to the spring theory is that they wouldn't be affected by sitting around, e.g., a spring problem would likely be more consistent, or at least not triggered solely by sitting.
- There’s likely some electrical gremlin plaguing me. I’ve already ruled out the battery, but am wondering if my shifter position sensor is bad. If I recall correctly, I could get a new one for about $125 USD, likely not much more than a dealer code reading. Everything else electrical in the car works fine. The codes indicate some intermittent electrical faults, but since many were “stored,” I have no idea of how relevant they are.
- Otherwise I’m at a loss. Any thoughts you all have would be MUCH appreciated.
Get codes cleared (I’m not sure if last mechanic did this; they didn’t charge me for a half hour of work), and then try to recreate problem and read codes again.
Maybe replace shift position sensor; depends somewhat on what you all have to say. Otherwise, I'm at a bit of a loss. And as noted, the problem is annoying, but not really keeping me from using the car, especially once it's back in more regular use.
Attached are photos of the codes from the Star Diagnostic system that the mechanic kindly gave me.
Thanks for reading and have a great day!
