Pd09: Ref Lo

Ignition Ground Voltage. Display shows the voltage difference between CKT 453 (ignition ground) and PCM ground shifted 2.5 volts. A reading of 2.500 volts means the ignition and PCM grounds are at the same voltage. A reading of 1.000 means the ignition ground voltage is 1.5 volts lower than the PCM ground and a reading of 3.500 means the ignition ground voltage is 1.0 volt above the PCM ground. Display shows ignition ground voltage level from .003 to 4.970 volts.