SMG Problems

[beyondm3]

My '02 M3 SMG (125k mi) started having problems recently. When the car is cold, it starts up instantly and the SMG works like a charm. No problems, no complaints under any type of load. However, when I shut off the car (when it is hot after being driven) it won't start again. The SMG remains in neutral and the car refuses to start, I can move the gear selector to the "R" and "1" position, but the gear will not be selected. No starting procedures take place.

I pulled the codes using the Peake tool, I got an exhaust temperature sensor code and I believe the SMG Safety Concept code (couldn't find much on this).

Through logic, I thought maybe it was the temp sensor on the transmission, so I replaced that. This did not fix it. I did not think it would be the exhaust code as in my mind, I did not think this would affect the SMG, from brief research it would only make the car run either rich or lean (don't recall the specifics.)

Now that I have typed this out, it makes me begin to think about replacing the gear position sensor but it still boggles the mind a bit seeing how the car runs perfect from a cold start.

I have read several posts regarding SMG issues and I can't quite find one that replicates my issues. I was hoping someone might be able to chime in with a similar experience or perhaps some insight as it would be greatly appreciated.

[maw1124]

Isn’t that the temp sensor failing? Google “smg hot start” and tons pop up. I haven’t had the problem, so I don’t know if the temp sensor on the transmission you replaced is different from the one on the SMG hydraulic unit. I think it’s the second one that goes bad.

maw

[oceansize]

If you haven't replaced the SMG salmon relay in a while do that first. Not familiar with Peake but you really need a BMW specific code reader since what you have are generic codes that no one here will be able to help with. You can use INPA available via standard tools link here.

Edit: With INPA you will be able to see if your temperature sensor found on the SMG pump is working.

[oceansize]

Also test your pump motor while hot by doing this, just for a second or two to make sure the motor will run as you don't want to build up too much pressure.

[beyondm3]

Isn’t that the temp sensor failing? Google “smg hot start” and tons pop up. I haven’t had the problem, so I don’t know if the temp sensor on the transmission you replaced is different from the one on the SMG hydraulic unit. I think it’s the second one that goes bad.

maw

So I looked on real oem and only found the one in the transmission. I assumed it fed to the SMG system as well. Perhaps I need to go in for another look. Thanks, definitely worth looking into again.

[beyondm3]

If you haven't replaced the SMG salmon relay in a while do that first. Not familiar with Peake but you really need a BMW specific code reader since what you have are generic codes that no one here will be able to help with. You can use INPA available via standard tools link here.

Edit: With INPA you will be able to see if your temperature sensor found on the SMG pump is working.

I did the salmon relay probably about 6 months ago thinking this was initially the issue, however back the the problem was not as prominent as it is now. I don't daily the car so it was sporadic and then became more of a recurring theme.

[oceansize]

Could be clutch slave cylinder so try this. Also clock how long it takes to prime your pump the first time from completely cold as this will give you some idea of your pump motor's health.

[maw1124]

So I looked on real oem and only found the one in the transmission. I assumed it fed to the SMG system as well. Perhaps I need to go in for another look. Thanks, definitely worth looking into again.

See Page 6 and Page 9 on the attached.

"Temperature Sensors -- Two NTC sensors are used for measuring Gearbox oil temperature and hydraulic fluid temperature."

I don't know where I found this, but it's one to download and keep for SMG owners.

Cheers,

maw

BMW E46 M3 -- SMG Manual.pdf

[sapote]

low oil pressure when hot could mean weak pump motor or too much internal leak.

[oceansize]

low oil pressure when hot could mean weak pump motor or too much internal leak.

Sapote you are back. What took you so long?

[ATB88]

Sapote you are back. What took you so long?

sapooooteeeeeee 😻

[beyondm3]

See Page 6 and Page 9 on the attached.

"Temperature Sensors -- Two NTC sensors are used for measuring Gearbox oil temperature and hydraulic fluid temperature."

I don't know where I found this, but it's one to download and keep for SMG owners.

Cheers,

maw

BMW E46 M3 -- SMG Manual.pdf

Thanks this helps a lot. I did look around for some photos of the hydraulic unit last night. I believe I see where it goes. Now I just need to get to it.

[oceansize]

Here is a video I took of INPA in action where you can see Gearbox Temps, Hydraulic Temp, and Hydraulic Pressure.

https://www.youtube.com/watch?v=ElFO0_sfoMQ

[sapote]

Sapote you are back. What took you so long?

Too busy with other house projects, and didn't know this new website up and running. It's great to see familiar faces here again.

[beyondm3]

Old thread but I finally got around to replacing the temp sensor on the hydro unit. It wasn't as bad as I thought it would be to get to but this did not solve my problem. Despite this I drove the car from SC to FL (350 miles) since I now have the space for the car, I was able to do it without stopping and thankfully there was no traffic but there was a ton of rain and some hail. I'm gonna try to get the laptop hooked up to it this weekend to see if I can get more details.