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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 01-19-2013, 07:14 AM   #21
roadtrip1098
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Join Date: Aug 2011
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My Ride: 04 M3 SMG LSB
FYI there's a pretty good DIY on the change out with pretty pics and everything. I think it's called Fix your SMG or something.
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Old 02-03-2013, 06:53 PM   #22
KCCOusmc10
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I have found the cause of this horrible flaw of the SMG transmission issue and it leads to the Pump temp sensor being mounted way too close to the engine. As a result, while you are sitting in traffic (with no airflow to cool it off it gets hotter and hotter) the HYD Pump temp sensor picks up heat from the engine and sends a signal to the ECU telling it the HYD fluid is "too hot." This is not the actual case. The result is the circuit that tells your pump to charge the accumulator is momentarilly disabled. You have two or 3 shifts left in the accumulator and after that there is not enough pressure to make the next gear so it drops to nuetral. after about 15-30 seconds the circuit is momentarilly restored and the accumulator charges again...the cycle repeats over and over again untill you can get on the highway or just simply shut the car off and let it cool for at least half an hour.

To stop this problem from happening i experimented and read through schematics for 3 days and what i came up with worked for me and it also worked for another member of this forum whom i was sharing ideas with. The best part is it it costs about 5 bucks if you do it yourself.

Take a 500-1K ohm heat resistant resistor and splice it in series with the temp sensor. its that simple. it takes about 20 Minutes start to finish. i waited about a week to post this to make absolutly sure the problem was gone. you can access the connector that goes from the ECU to the HYD pump from unterneath the car just "inboard" of the front driver side tire. there are 18 wires on it i think and all sorts of colors. the wire you want is the SOLID WHITE WIRE. Just cut it, splice in the resistor and wrap it up tight and your done.

Now keep in mind that this does not keep your car from heating up the actual sensor but instead, adds a temp "bias" for your ECU to not allow it to reach the over temp voltage. This in my opinion is safe, effective and a dream come true for the price. Remember, the only possible effect of hyd fluid over heating is premature wear of the pump itself...chances are if you have this problem, you were told you need to replace the pump by the mechanics for about $3500...Sounds like we have nothing to lose right? Especially since the hyd fluid isnt really overheating in the first place and its just the engine heating up the sensor that is aprox 3/4'' away from it.
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Old 02-03-2013, 11:56 PM   #23
0-60motorsports
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Quote:
Originally Posted by KCCOusmc10 View Post
I have found the cause of this horrible flaw of the SMG transmission issue and it leads to the Pump temp sensor being mounted way too close to the engine. As a result, while you are sitting in traffic (with no airflow to cool it off it gets hotter and hotter) the HYD Pump temp sensor picks up heat from the engine and sends a signal to the ECU telling it the HYD fluid is "too hot." This is not the actual case. The result is the circuit that tells your pump to charge the accumulator is momentarilly disabled. You have two or 3 shifts left in the accumulator and after that there is not enough pressure to make the next gear so it drops to nuetral. after about 15-30 seconds the circuit is momentarilly restored and the accumulator charges again...the cycle repeats over and over again untill you can get on the highway or just simply shut the car off and let it cool for at least half an hour.

To stop this problem from happening i experimented and read through schematics for 3 days and what i came up with worked for me and it also worked for another member of this forum whom i was sharing ideas with. The best part is it it costs about 5 bucks if you do it yourself.

Take a 500-1K ohm heat resistant resistor and splice it in series with the temp sensor. its that simple. it takes about 20 Minutes start to finish. i waited about a week to post this to make absolutly sure the problem was gone. you can access the connector that goes from the ECU to the HYD pump from unterneath the car just "inboard" of the front driver side tire. there are 18 wires on it i think and all sorts of colors. the wire you want is the SOLID WHITE WIRE. Just cut it, splice in the resistor and wrap it up tight and your done.

Now keep in mind that this does not keep your car from heating up the actual sensor but instead, adds a temp "bias" for your ECU to not allow it to reach the over temp voltage. This in my opinion is safe, effective and a dream come true for the price. Remember, the only possible effect of hyd fluid over heating is premature wear of the pump itself...chances are if you have this problem, you were told you need to replace the pump by the mechanics for about $3500...Sounds like we have nothing to lose right? Especially since the hyd fluid isnt really overheating in the first place and its just the engine heating up the sensor that is aprox 3/4'' away from it.
Thanks for doing the research. I am wondering if anyone has tried a heat blanket on the pump or a cooling duct installed directing air to the pump when the car is moving...
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Old 02-08-2013, 01:47 PM   #24
steve bettencourt
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Location: ajax ontario canada
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I was told by my engineer that if you change the four ball and springs in the pump , that's what causes most of the problems good luck
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Old 09-06-2013, 12:02 PM   #25
rruiter
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My Ride: 04 M3 SMG2 Coupe
Quote:
Originally Posted by KCCOusmc10 View Post
I have found the cause of this horrible flaw of the SMG transmission issue and it leads to the Pump temp sensor being mounted way too close to the engine. As a result, while you are sitting in traffic (with no airflow to cool it off it gets hotter and hotter) the HYD Pump temp sensor picks up heat from the engine and sends a signal to the ECU telling it the HYD fluid is "too hot." This is not the actual case. The result is the circuit that tells your pump to charge the accumulator is momentarilly disabled. You have two or 3 shifts left in the accumulator and after that there is not enough pressure to make the next gear so it drops to nuetral. after about 15-30 seconds the circuit is momentarilly restored and the accumulator charges again...the cycle repeats over and over again untill you can get on the highway or just simply shut the car off and let it cool for at least half an hour.

To stop this problem from happening i experimented and read through schematics for 3 days and what i came up with worked for me and it also worked for another member of this forum whom i was sharing ideas with. The best part is it it costs about 5 bucks if you do it yourself.

Take a 500-1K ohm heat resistant resistor and splice it in series with the temp sensor. its that simple. it takes about 20 Minutes start to finish. i waited about a week to post this to make absolutly sure the problem was gone. you can access the connector that goes from the ECU to the HYD pump from unterneath the car just "inboard" of the front driver side tire. there are 18 wires on it i think and all sorts of colors. the wire you want is the SOLID WHITE WIRE. Just cut it, splice in the resistor and wrap it up tight and your done.

Now keep in mind that this does not keep your car from heating up the actual sensor but instead, adds a temp "bias" for your ECU to not allow it to reach the over temp voltage. This in my opinion is safe, effective and a dream come true for the price. Remember, the only possible effect of hyd fluid over heating is premature wear of the pump itself...chances are if you have this problem, you were told you need to replace the pump by the mechanics for about $3500...Sounds like we have nothing to lose right? Especially since the hyd fluid isnt really overheating in the first place and its just the engine heating up the sensor that is aprox 3/4'' away from it.
Is this still considered 'fixed' ?
Did you drive it in hot weather ? no more issues?
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Old 09-06-2013, 04:56 PM   #26
M3_CABRIO
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There are a few article related to the temp sensor, HCU Sensor, the Salmon Relay, and the resistor to the white wire. These parts are fairly inexpensive and can help the people that live in hot weather Which can be anywhere at times in the US.

There have been articles if you type in HCU or Hydraulic Control Unit

http://www.bmwcca.org/forum/index.ph...-bmw-n-a.3007/

http://www.aboutautomobile.com/Compl...c+Transmission

http://www.m3forum.net/m3forum/showthread.php?t=372262

Should be a starting point...
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Old 09-11-2013, 01:32 PM   #27
subsoniic
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was this ever resolved ? by replacing the actual temperature sensor ? im desperate !
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Old 07-13-2014, 08:07 PM   #28
BMWMPAGE
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Hey, what is the exact name of the part SMG Transmission Temperature Sensor for Hydraulic Pump, do you remember the part number?


Thanks a lot.
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