I bought a Dakota Digital GPS unit to hopefully solve an issue I'm having of the engine stalling when coming to a stop. Part # for the unit is GPS-5-2.
With the GPS unit in the setting mode it outputs a 60mph signal. To test, I hooked up my android tablet to the OBD port via a PLX Devices Bluetooth dongle and used Dash Command to display the info from the ECU.
From the VSS plug on the GM wiring harness, I connected the purple/white wire to the GPS unit and the other wire to ground.
I first tried Speed output #1 which is the "standard speedometer" output. VSS speed read zero. So, I tried Speed output #2, "AC speedometer". Now I got a reading on the VSS speed. With the GPS unit set to 54000 pulses, the VSS reading from the ECU was 32mph, and with the pulses set to 128000, the VSS read 75mph. I think that's probably close enough for the ECU to be happy, so I'll leave it at 128000 and see how it works.
Next step was to hook the GPS unit up to the KOSO speedometer. I cut the cable to the KOSO speed sensor. It has three wires: red = power, black = ground, and white = signal. I taped up the black and red and connected the white wire to the Speed Output #1 on the DD GPS. With the GPS unit in setting mode, the KOSO read 225mph :stunned:. After some trial and error, I got it to read 61mph. Close enough. The settings I used on the KOSO were 25 sensor points and 310mm tire diameter.