the iscv gets driven by a pulsed waveform (one terminal of valve has 12V supply, other terminal pulses low driven by pin34) - if you measure pin34 with a multimeter with respect to ground, what you will measure is the "average" voltage drive determined by the on/off ratio - as the valve drive reduces to close the valve, the average measured voltage will increase and conversely as the valve is driven open the average voltage measured at pin34 wil decrease
This may seem odd, but it's due to the active "on" signal being low.