IIUC, the SCV (Spill Control Valve, also called SPill Valve or SPV) controls the volume of fuel injected for each and every time one injector fires. The radial pump builds up pressure for each injection, increasing pressure until the injector opens, then the SCV will open up a passage back to the low pressure side in order to stop the injection of fuel, thus controlling the volume.
So, the SCV is very busy, opening and closing 3 times for every revolution of an i6 engine. With the steep 150 v pulses, if there is any abnormal resistance in any plug or connector between SCV, EDU and power supply (0 volt (ground) and +12 volt), the SCV will start malfunctioning.