The 12V in is the voltage to control the exhaust valve so you are correct in your assumption. The 2 voltages switch polarity depending on if it is opening or closing the valve. The ramp out simulates the resistance of the valve pot. What then input to the ECU is other than this ramp I don't know. Impedance? don't know but the existing CCT works fine so as far as the output from the AD5227 is concerned it should not change.