Transmission Code P2740 Help
Thread Starter
Newbie
Joined: Dec 2025
Posts: 1
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From: NorCal
2015 E63S Wagon
Transmission Code P2740 Help
Hey there, long time listener, first time caller.
Firstly, I have searched all over MBW, FCP, the Interwebs, etc., and have been skunked. Okay...
I took delivery of a 2015 E63S wagon a couple weeks ago. 62k miles. Purchased out of state. I've bought cars out of state many, many times without issue. PPI done and checked out good enough to get the deal done. Got it back to California and went to smog it...didn't pass.
Smog shop came back with a code that the PPI shop didn't find. Permanent code P2740, Transmission Fluid Temp Sensor "B" Circuit. Took the car to a local MBZ shop to take care of a couple of things called out on the PPI and to check out what the smog shop found. They have a proper scanner and they didn't find the code either. They took it to another smog shop, and sure enough, it popped right up.
So, my questions are:
1) Have any of you had this come up before?
2) Is this a Do Not Drive situation?
3) I've driven high performance cars where the trans can be a little clunky until it warms up, and this trans seems to be that way. Is this a normal behavior?
The local shop said to drive it for a couple hundred miles and a couple weeks to try and get the code to go away, but also didn't seem to know exactly what that code meant. Both the PPI shop and the local shop are reputable and mostly deal with MBZ. The local shop told me if driving it didn't get the code to go away, then take it to the dealer. If there was a dealer closer than 45 minutes away to me, I would have done that on day 2, but logistically it can be really tough to get there.
Appreciate your insights and thoughts on this!
Cheers,
TDB
Firstly, I have searched all over MBW, FCP, the Interwebs, etc., and have been skunked. Okay...
I took delivery of a 2015 E63S wagon a couple weeks ago. 62k miles. Purchased out of state. I've bought cars out of state many, many times without issue. PPI done and checked out good enough to get the deal done. Got it back to California and went to smog it...didn't pass.
Smog shop came back with a code that the PPI shop didn't find. Permanent code P2740, Transmission Fluid Temp Sensor "B" Circuit. Took the car to a local MBZ shop to take care of a couple of things called out on the PPI and to check out what the smog shop found. They have a proper scanner and they didn't find the code either. They took it to another smog shop, and sure enough, it popped right up.So, my questions are:
1) Have any of you had this come up before?
2) Is this a Do Not Drive situation?
3) I've driven high performance cars where the trans can be a little clunky until it warms up, and this trans seems to be that way. Is this a normal behavior?
The local shop said to drive it for a couple hundred miles and a couple weeks to try and get the code to go away, but also didn't seem to know exactly what that code meant. Both the PPI shop and the local shop are reputable and mostly deal with MBZ. The local shop told me if driving it didn't get the code to go away, then take it to the dealer. If there was a dealer closer than 45 minutes away to me, I would have done that on day 2, but logistically it can be really tough to get there.
Appreciate your insights and thoughts on this!
Cheers,
TDB
Out Of Control!!
Joined: Apr 2019
Posts: 12,003
Likes: 6,827
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Tranny Temp Code
Hey there, long time listener, first time caller.
Firstly, I have searched all over MBW, FCP, the Interwebs, etc., and have been skunked. Okay...
I took delivery of a 2015 E63S wagon a couple weeks ago. 62k miles. Purchased out of state. I've bought cars out of state many, many times without issue. PPI done and checked out good enough to get the deal done. Got it back to California and went to smog it...didn't pass. Smog shop came back with a code that the PPI shop didn't find. Permanent code P2740, Transmission Fluid Temp Sensor "B" Circuit. Took the car to a local MBZ shop to take care of a couple of things called out on the PPI and to check out what the smog shop found. They have a proper scanner and they didn't find the code either. They took it to another smog shop, and sure enough, it popped right up.
So, my questions are:
1) Have any of you had this come up before?
2) Is this a Do Not Drive situation?
3) I've driven high performance cars where the trans can be a little clunky until it warms up, and this trans seems to be that way. Is this a normal behavior?
The local shop said to drive it for a couple hundred miles and a couple weeks to try and get the code to go away, but also didn't seem to know exactly what that code meant. Both the PPI shop and the local shop are reputable and mostly deal with MBZ. The local shop told me if driving it didn't get the code to go away, then take it to the dealer. If there was a dealer closer than 45 minutes away to me, I would have done that on day 2, but logistically it can be really tough to get there.
Appreciate your insights and thoughts on this!
Cheers,
TDB
Firstly, I have searched all over MBW, FCP, the Interwebs, etc., and have been skunked. Okay...
I took delivery of a 2015 E63S wagon a couple weeks ago. 62k miles. Purchased out of state. I've bought cars out of state many, many times without issue. PPI done and checked out good enough to get the deal done. Got it back to California and went to smog it...didn't pass.
Smog shop came back with a code that the PPI shop didn't find. Permanent code P2740, Transmission Fluid Temp Sensor "B" Circuit. Took the car to a local MBZ shop to take care of a couple of things called out on the PPI and to check out what the smog shop found. They have a proper scanner and they didn't find the code either. They took it to another smog shop, and sure enough, it popped right up.So, my questions are:
1) Have any of you had this come up before?
2) Is this a Do Not Drive situation?
3) I've driven high performance cars where the trans can be a little clunky until it warms up, and this trans seems to be that way. Is this a normal behavior?
The local shop said to drive it for a couple hundred miles and a couple weeks to try and get the code to go away, but also didn't seem to know exactly what that code meant. Both the PPI shop and the local shop are reputable and mostly deal with MBZ. The local shop told me if driving it didn't get the code to go away, then take it to the dealer. If there was a dealer closer than 45 minutes away to me, I would have done that on day 2, but logistically it can be really tough to get there.
Appreciate your insights and thoughts on this!
Cheers,
TDB
Somebody is gonna need to troubleshoot WHY your ATF has a "low temp" issue.
Use your favorite scanner/Xentry or let your trusted MB specialist handle this.
it is not flagging an open circuit. It sounds like a genuine TCU concern, not a glitch (reboot/clear?)
Don't rush to call "bad sensor" to pull tranny out: "We'll know for sure once tranny is all opened up..."
It can be low ATF level - Any visual leaks then ??
Look at how temperature rises?
Circuit-B: then what does circuit-A show ?
It's surprising California SMOG station fails your inspection on misc tranny fault... I pass SMOG with TWO active ECU faults (no CEL)
Go to a different SMOG shop inspection then fix tranny DTC on your schedule...
Last edited by CaliBenzDriver; Dec 24, 2025 at 04:05 PM.
