[sorry] I can't find my VSS wire [/sorry]
 

I have a 2000 Subaru Impreza, and I cannot find my VSS lead.

Yes, I searched (both the forums AND my car). Rostra said that the VSS wire would be green/yellow under my instrument panel. Then, I found this document (see attachment) that said it would be in the same location and also green/yellow. Conclusion: I should search for a green/yellow line under my dash, and test the voltages on it.

So, this is what I did. I found the (only) green/yellow wire in an 18 pin connector and jammed one end of my multimeter in it, the other end firmly attached the the vehicle ground through where my CD player is. When I turn the key (engine not on) I get 14.2v. When I turn the engine on, I get 14.2v. When I drive around the parking lot, I get 14.2v (no fluctuation). GRR

The signal I'm looking for is between 0-5v, so this can't be the wire! After looking at some schematics (and to some mechanics) there are two options left: find the VSS sensor and follow it up into the car, or find where it plugs into the ECU and tap into it there.

Problem with option #1: The sensor is located in my transmission, apparently, and I have no way to jack my car. I drove two wheels over a curb and saw nothing promising.

Problem with options #2: The ECU in my car is under the floorboard in the passenger seat, a real pain to get out. And once I get it out, I have no way of knowing exactly which of the bajillion wires it is.

My car (4dr, 2000 subaru impreza sedan) is "unusual," in the sense that it is unlike the models before it and after it. It is also very uncommon. I have found no wiring harness diagrams or anything specifically for my car, they've all been for similar models.

What should I do? I am very (truly) sorry for making such a stupid thread like this, as there have been many before, but I really am stuck here. Can anyone help me?

Thank you,

IHateMayonnaise

another place to find VSS is your speedometer, though it might be even more work to disassemble the dash.

This Rostra doc says that the VSS signal is at:

Passenger Floor-96 pin conn @ ECM
Pos. 93 Loc3 35 pin conn @ ECM Pos24

for a 99-04 Subaru Impreza.

Since they don't give diagrams in that doc, it's hard to tell how they do their positioning. Their other one, for '86-'95 vehicles, shows pictures of the connectors, so it's easier to find where it is.

What I would do is, try the other wires behind the speedometer. Since you're not cutting into any wires, it shouldn't be too hard. Also, I don't think you're necessarily looking for a 0-5V signal (I think it could also be 0-12?), just one that changes with speed.

Otherwise, I would go for the ECU option. Start with what the rostra data has, you'll probably find that green/yellow wire there.

Thanks for the advice. If at all possible I would prefer not to completely take my dash apart -- thus far I have just been resting my head on my clutch petal with my feet sticking out the door. I suppose the next step would be to start taking it apart...

Every place I've seen has said that the VSS signal will be between 0-5v, not true?

I think it depends upon the system in the vehicle. Don't feel bad, I cannot find a VSS in my truck. Various speed sensors, but no VSS. Frustrating. 06s have one. You might look at AVIC411.com • Index page and see if they have anything for you.

Well, I did some digging and pulled what I think I need to create a VSS signal on my truck. I bought the following from Radio Shack:
276-0145 NPN infrared phototransistor
271-1120 1.5k ohm resistors
276-0143 high output infrared LED
271-152 100 ohm 1watt resistors

I plan to connect as follows in the picture, and run the wire from the phototransisor to the MPGuino. It will read signals from the LED as the driveshaft yokes spins by.

I found mine by jacking my car's driver's side front tire up off the ground (with parking brake on!), and searching through all the pins connected to my ECU (computer) while rotating the driver's side tire. Sure enough, it was the last one i could have checked, and it was also green and yellow (I don't remember if it was G/Y or Y/G...) I don't drive a sube, but the technique may work for you anyhow.