LS7 Speed sensor troubles

[Ultima GTR]

Guys,

I've got a problem with my Speed Sensor wiring. I'm reading 2.5 VDC off the harness and that doesn't seem to be enough voltage to trigger my aftermarket speed sensor. Does anyone know what voltage should be coming off the harness?

Thanks, Chris

LS7 Crate motor
LS7 after market harness

[LSX378]

Guys,

I've got a problem with my Speed Sensor wiring. I'm reading 2.5 VDC off the harness and that doesn't seem to be enough voltage to trigger my aftermarket speed sensor. Does anyone know what voltage should be coming off the harness?

Thanks, Chris

LS7 Crate motor
LS7 after market harness

The ECM VSS line sits at around 2.5V. The VSS sensor output should modulate this toward +/- 2.5V.

[Ultima GTR]

I've been up and down the net looking for a simple wiring diagram of a typical GM VSS. Any chance you can describe the hookup to a typical photo sensor?

The speed sensor I'm using for my AIM Data logger has three wires. BRN (12vdc source), Blue (ground), and the Black (trigger wire). I'd like to use another one of these for teh VSS, any idea if this sensor could work for the LS ECU?

Thanks, Chris

[gmtech16450yz]

This might help...
('09 'Vette)

[LSX378]

I've been up and down the net looking for a simple wiring diagram of a typical GM VSS. Any chance you can describe the hookup to a typical photo sensor?

The speed sensor I'm using for my AIM Data logger has three wires. BRN (12vdc source), Blue (ground), and the Black (trigger wire). I'd like to use another one of these for teh VSS, any idea if this sensor could work for the LS ECU?

Thanks, Chris

Per GMTechs diags: 72 is the ground side, 71 the signal side of the VSS. Your trigger needs to go to 71, ground to ground on 72, 12V to 12V somewhere. The GM VSS is hall effect so generates its own voltage/current to swing the voltage on pin 71.

There is a good chance the VSS will work if you are producing a rough square wave from your setup that runs 2.5V +/- 2.5V max.

[Ultima GTR]

Thanks Guys. I pulled a VSS out of an old GM transmission that a buddy had and was able to get a MPH reading off my OBDII reader.

Chris