Ref. Volts Low

Display shows Ignition Ground Voltage in volts. The PCM keeps the voltage difference between ignition ground and PCM ground shifted by approximately 2.5 volts. The scan tool rescales the 2.5 volts to indicate 0 volts on the display. A circuit reading of 2.500 volts means the ignition and the PCM grounds are at the same level which would be displayed as 0 volts on the scan tool. A circuit reading of 1.000 volt means the ignition ground voltage is 1.5 volts lower than the PCM ground. A circuit reading of 3.500 volts means the ignition ground voltage is 1.0 volt above the PCM ground.