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Old 02-03-2013, 06:53 PM   #22
KCCOusmc10
Registered User
 
Join Date: Feb 2013
Location: Jacksonville, NC
Posts: 1
My Ride: 2003 M3
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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