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Join Date: Nov 2013
Location: West Newton,MA
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From you description in your latest post it indeed appears to me that TA-1 is broken. You say it resists when it is connected to the circuit board but it is NOT powered. It should only resist when it is powered ON. Essentially, when the TA is CLOSED, the power electronics connect each of the terminals of the motor to ground/negative. So, by doing so, they are also connected together and thus shorted. When the TA is NOT powered, the circuit electronics and thus the MOSFETs are not driven and are an open circuit. It becomes a high impedance (disconnected) connection as long as the motor terminal voltage stays below 1.4V (2 diode drops). There will be no motor resistance. When the voltage spikes above 1.4V there will be motor resistance as the (unintentional) diodes start conducting, forming a short. But once the voltage drops below 1.4V, resistance goes away. Overall you would expect less resistance when not powered.
If you say TA closes slowly when NOT powered you either have a circuit board short (very likely broken MOSFET(s)) and/or a mechanical problem.
Here is a video of my setup that shows it all one more time in action. Notice that my TA is notchy near its closing position. A mechanical issue! This is what it produced my TA errors. In this case, it is a combination of worn gears and the need for lubrication.
Most ECUs these days runs hosts of self-tests and are able to "judge themselves" to great extend. This is what the OEMs require, not just BMW. That is a good thing. Try to debug this issue considering you have no fault codes. Where do you start in these systems. Very obscure issue at that point.
If you are up for it, send me your broken TA for more analysis. Send me a PM.
Last edited by rt7085; 22nd June 2016 at 04:23 AM.