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post #11 of 14 Old 22nd June 2016, 02:58 AM Thread Starter
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Originally Posted by rt7085 View Post
No MOSFETs block current only on one direction. There is an unintentional diode across them (internally) that causes the 'short'.

The intermittence is a result of the internals of the TA not passing some kind of self test. If it fails it throws an error status in the CAN response and turns into a vegetable until the next power cycle.
Great. The insane TA is judging itself. Some weed those BMW engineers must have been smoking that night.

So when everything works and the car comes up in ignition 2 (not running but ignition on), something happens between then and the next time I turn it on.

I had both TAs opening fine with the component test (the 20 second one). TA-2 would snap shut, but TA-1 would drift shut and lead to the limp mode. Why is this? What would cause the motor to provide resistance like that in one TA and not the other?
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post #12 of 14 Old 22nd June 2016, 04:05 AM
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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.
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post #13 of 14 Old 22nd June 2016, 12:37 PM Thread Starter
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Yes. It resists when connected to the circuit board and there is no power. It double resists when a short is applied across the motor terminals. TA-2 is great though. When running the valve test through the ISTA "test plan" on throttle valve actuator error codes, the butterfly valves flap easily and everything passes. TA-1 just sits there stunned. But when I first put it back in, everything worked fine. It was only when I ran the Component triggering in ISTA that everything went south. All throttle valves opened fine. TA-2 slammed shut at the end of 20 seconds. TA-1 drifted (relatively) shut. Then I got the error codes again.

That is when I started the investigation and stumbled upon the resistance of the motor/gears in the TA to returning to 'rest' position (closed on the throttles) when the motor contacts were connected to the circuit board with NO power.

Last edited by gmak; 22nd June 2016 at 02:05 PM.
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post #14 of 14 Old 22nd June 2016, 02:01 PM Thread Starter
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