These still bug me!
As we know there are two variants, the original 4 pin and the 3 pin.
The main difference being that the 4 pin used a 12V supply and the 3 pin does not.
From the pictures I have seen the 4 pin was more complicated internally than the later 3 pin which basically has a NTC resitor and 2 microswitches and an expanding pellet which presumably trips the mircoswitches.
On the S2 one function of the MFTS is to alert the ecu to an overheat situation and deactivate the boost control reverting to the mechanical boost level of the spring only. This feature does not appear in the S6 AAN. I am not sure about the S4 AAN.
According to the factory documentation this function is achieved by a signal out of the MFTS to pin 46 (ABY). This is supposedly either above 2V for the boost control to be active and below 2V for it to be inactive.
So we know the original 4 pin had a 12V supply therefore its possible that a voltage could be sent out another pin, perhaps through some resitance that varied due to temperature. However the 3 pin does not! It also does not explain how disconnecting the MFTS connector can restore boost if the MFTS is faulty because that can only be removing any signal from pin 46! That implies the ecu is expecting to see an open signal rather than a specific voltage for the boost control to be active.
If we go back to the 3 pin, the two mircoswitches must have the same function. They are either open or closed. I am assuming that if they close they are earthed aginst the body of the sensor much like the NTC resistor is for providing the change in resistance for the temp gauge. I have previously experimented with measuring the changing resistance of the 3 pin by measuring between the temp gauge pin and the body of the MFTS. That does not work on the 4 pin but I am assuming that this MFTS needs the 12V to generate the signal somehow. It also explains why replacing a 3 pin with a 4 pin MFTS does not seem to work on cars originally equipped with a 3 pin MFTS such as A6 C4's.
So we still have some anomolies. Was the boost control deleted from the S6 because the 3 pin MFTS, which was introduced around the time of the A6/S6 facelift from the 100, cannot perform the same function, i.e. output a voltage? I am pretty sure the S6 does not even have a wire to pin 46 even if the code in the ecu is there.
Is the factory documentation incorrect about a voltage on the S2 models? We seem to have established that removing any signal restores boost which is contary to the information pushlished. If it is a voltage it would seem to suggest that there is no way the 3 pin is a suitable replacement as it cannot produce voltage of its own. It can only produce either an open or closed (earthed) signal.
If the 3 pin MFTS can produce voltage on its own then I think I have discovered the solution to increasing energy costs in the UK!
Discuss!
As we know there are two variants, the original 4 pin and the 3 pin.
The main difference being that the 4 pin used a 12V supply and the 3 pin does not.
From the pictures I have seen the 4 pin was more complicated internally than the later 3 pin which basically has a NTC resitor and 2 microswitches and an expanding pellet which presumably trips the mircoswitches.
On the S2 one function of the MFTS is to alert the ecu to an overheat situation and deactivate the boost control reverting to the mechanical boost level of the spring only. This feature does not appear in the S6 AAN. I am not sure about the S4 AAN.
According to the factory documentation this function is achieved by a signal out of the MFTS to pin 46 (ABY). This is supposedly either above 2V for the boost control to be active and below 2V for it to be inactive.
So we know the original 4 pin had a 12V supply therefore its possible that a voltage could be sent out another pin, perhaps through some resitance that varied due to temperature. However the 3 pin does not! It also does not explain how disconnecting the MFTS connector can restore boost if the MFTS is faulty because that can only be removing any signal from pin 46! That implies the ecu is expecting to see an open signal rather than a specific voltage for the boost control to be active.
If we go back to the 3 pin, the two mircoswitches must have the same function. They are either open or closed. I am assuming that if they close they are earthed aginst the body of the sensor much like the NTC resistor is for providing the change in resistance for the temp gauge. I have previously experimented with measuring the changing resistance of the 3 pin by measuring between the temp gauge pin and the body of the MFTS. That does not work on the 4 pin but I am assuming that this MFTS needs the 12V to generate the signal somehow. It also explains why replacing a 3 pin with a 4 pin MFTS does not seem to work on cars originally equipped with a 3 pin MFTS such as A6 C4's.
So we still have some anomolies. Was the boost control deleted from the S6 because the 3 pin MFTS, which was introduced around the time of the A6/S6 facelift from the 100, cannot perform the same function, i.e. output a voltage? I am pretty sure the S6 does not even have a wire to pin 46 even if the code in the ecu is there.
Is the factory documentation incorrect about a voltage on the S2 models? We seem to have established that removing any signal restores boost which is contary to the information pushlished. If it is a voltage it would seem to suggest that there is no way the 3 pin is a suitable replacement as it cannot produce voltage of its own. It can only produce either an open or closed (earthed) signal.
If the 3 pin MFTS can produce voltage on its own then I think I have discovered the solution to increasing energy costs in the UK!
Discuss!
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