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Discussion Starter · #1 ·
I had a 5MT swap done recently to my forester 2000 JDM S/tb equivalent to V5/6 GC8 ej20 . Been trying to get the vehicle speed sensor to work without any luck. Current transmission is from a GC8 v4 5MT with the old VSS 2 pin output, i've tried linking the VSS signal pin directly into the ECU and have the other pin grounded, that didn't work. I've also read that i might be able to make it work by re-pin it to the cluster first then it will send the right pulse/signal to the ECU, but i am not sure which pin to try on the cluster. Any one with swap experience can point me to right direction? Much appreciated!

p.s. not running any signal through the TCU. i've removed it completely, everything else runs perfectly except for the speedometer.
 

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Take all this with a grain of salt, because I kind of pieced it together from reading a bunch of forum threads on both Subaru forums and on Volkswagen forums (from folks talking about Subaru swaps). I believe this is accurate though. If I'm wrong, please correct me so I can edit this post and then hopefully all of this information will finally be in one place. :)

The 3 pin VSS is a Hall effect sensor that takes 12v and ground and outputs a 5v digital (square wave) signal at 4 pulses/rev.
The 2 pin VSS is a VR sensor that outputs an AC (sine wave) signal that increases in frequency and amplitude as the sensor spins faster.

For cars that had a 2-pin VSS stock (and cars that had a mechanical speedo), the VSS is hooked up to the cluster directly and the cluster itself outputs a 5v square wave signal that I believe is functionally the same as the signal from the 3-pin VSS.

For cars that had a 3-pin VSS stock I think the signal either goes to the ECU and then the ECU sends it on to the cluster or it's split and goes to both. Not quite sure.

Anyways, if you have a cluster that was meant to go with a 2-pin VSS find the wiring diagram for your car and hook the 2-pin VSS signal up to the cluster and I think it should output the right signal for the ECU. If you have a cluster that expects a 3-pin VSS signal, get yourself a 3-pin VSS: It slots right in where the 2-pin VSS is.

No one is likely to be able to tell you exactly what pin to use (unless they have the exact same year/model car from the same market as you) because wiring seems to be the one thing that Subaru was happy to change at the drop of a hat.
 

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Discussion Starter · #3 ·
Thank You Johnxx! From my research, its exactly what you mention above. 2 wire vs 3 wire differences. Maybe i should try hooking the 2 wire one directly to the cluster, it then should be able to provide the proper signal to the ECU, only thing with that is i need help on figuring out which pin is for the sensor on the cluster :(

Not exactly sure what my previous auto transmission run on, as its got 3 different sesnor merged into one then it goes to the auto tran inhibitor switch.

Ive found info on how to get the 3 wire VSS to work, but for the 2 wire VSS not much info in it. maybe worst case i should pick up a 3 wire one and save the hassel.

Thanks again John!
 

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There's just not a lot of Forester talk on this forum so I kinda doubt anyone is going to know the right wire off the top of their head. Also, I'm assuming this is a RHD car?
Anyways, it's probably time to grab the FSM that's closest to your car and start using it to track stuff down:
 

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Discussion Starter · #5 ·
There's just not a lot of Forester talk on this forum so I kinda doubt anyone is going to know the right wire off the top of their head. Also, I'm assuming this is a RHD car?
Anyways, it's probably time to grab the FSM that's closest to your car and start using it to track stuff down:
I do have the fsm, though i am having trouble with it on where the pin should go. You have any experience on chart reading? And yes its a RHD car.

Ive attached some of the wiring chart below, which should be what we need. Theres a pin on the Cluster chart, should i try wiring the vss signal to that or i need to tee off the vss signal to both the cluster and the tcu?

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86557
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Ok, so this nicely confirms what I was talking about: Your cluster is meant to work with a 3-wire VSS. Take a look at the last diagram you posted. Notice a couple things:
  • The internal diagram for the gauge cluster specifically calls out that the VSS signal goes to an internal CPU: We can pretty safely infer that it's expecting a digital signal, probably at 5v, but ...
  • ... the real smoking gun is that on that same page the VSS pictured is a 3-wire VSS

(If that cluster expected a 2-wire VSS, we'd expect to see both wires from the 2-wire VSS go to the cluster, then we'd expect a separate signal wire labeled something like VSS2 going back from the cluster to the ECU.)

You either need a 3-wire VSS or you need to put together some type of electronic adapter circuit if you really can't get your hands on a 3-wire VSS locally.
 

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Discussion Starter · #7 ·
Excellent write up John! Thank,you so much for spending the time and read into this. And yes to your information, a 2 wire vss needs a bit of work to get it sending a new wave form/pulse to the ecu.

I will try to pick up a 3 wire vss and it should get it running. Assuming 3 wire one works.

According to the chart

  • Signal wire should go directly to the ecu.
  • 1 wire is for the 12v
  • 1 wire is for the ground

Correct me if i am wrong.

Thank you very much!
 

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That's my reading of the diagram too and what I've seen elsewhere. I'm about to test my 3-wire VSS for the first time in a couple days, so I'll let you know how it goes. I've definitely heard that they blow easily if wired up wrong, so be careful figuring out which pin is which. I saw a diagram from somewhere, but I can't remember where. I actually think the FSM might have the VSS wiring with a picture of the connector in the diagnostics section. Take a look around for that. Let me know if you can't find it and I'll go look for it again.
 

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Discussion Starter · #9 ·
found something from an very old post on other legacy forum. It explains how the 3 wire vss works as well as the pin layout. See if we can use this as reference. Hope it helps!

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Alright, I got a chance to test mine out and can confirm that pinout. Also, the 3-wire VSS doesn't generate a 5v square wave of any kind, it just connects to ground 4 times per revolution. The 5v part is generated by a pull-up resistor in the gauge cluster (and possibly the ECU, but I didn't test a stock ECU).

Here's another tidbit that's probably interesting to about 3 people total on the whole internet. For at least the '93-'96 Imprezas, If you have a cable (or I assume 2-wire VSS) speedo, the speedo itself generates a signal that is compatible with the 3-wire VSS and feeds that to the ECU. In the US I believe we only got a mechanical speedo in those years. That seems to be the case in Japan as well (judging by the JDM gauge clusters available on ebay). In the UK though, on the Impreza Turbo, they got a gauge cluster that expects a 3-wire VSS signal for the speedo and is otherwise pin-compatible to the USDM cluster. In fact, that cluster expects its digital VSS signal on the same pin that our clusters output the digital signal on.

That's a little wall of text, but the takeaway is that you can grab a UKDM cluster (with pretty red needles and a 7k RPM redline) and then swap your cable-speedo-drive for a a 3-wire VSS. Then just tee the signal from the 3-wire VSS into the wire that goes between the VSS2 output pin on the gauge cluster and the ECU's VSS2 input. Then install the UKDM cluster and you should get magic. Disclaimer: I didn't quite do that. Instead I opted to plug the VSS signal into my standalone and then used the standalone to drive the speedo, but the method should be the same. That let me fiddle with the scaling a bit to make up for the fact that I'm not running exactly stock height tires and have a different transmission than the cluster is meant to go with.
 

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Discussion Starter · #11 ·
John, good to hear from you again! Great write up as usual!

A little update on my trial today. Still trying to get my 2 wire vss to work with my current cluster.

#test 1
Using the TCU harness plugs, tried pinning each of the wire from the VSS to the correspinding pins. (signal to B55 pin 5, ground to B55 pin 9) Assuming one wire from the VVS is signal and the other one is ground. No luck with that. Switch up the wires and tired the same pins, no luck as well.

#test 2
Using the TCU harness plugs with the TCU plugged in. Pinning each wire to the corresponding pins
(signal to B55 pin 13, ground to B55 pin 21) nothing as well.

Ive dug up the full pinout from the FSM, not sure if i confused myself along the way, as the diagram suggest it should be linked up if my tcu is plugged it. Let me know if you can point out what i did wrong or what should i look into, ill attach the pinouts below.

I know i am very close to having this solved. 😢

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So, the 2-wire VSS is going to output an AC sine-wave, ranging from millivolts at low speed to probably a couple volts after you're up to speed. The key thing is both wires are signal. To use that signal with a gauge cluster that expects a 3-wire VSS "digital" signal you'll need to adapt it with some kind of circuit.

I know exactly nothing about the Subaru auto transmissions or their various TCUs and TCMs and whatever. That last diagram kinda makes it look like the TCU could accept a 2-wire VSS sine wave and output a digital signal. And the way it's wired seems to imply that it is actually only using "half" of the signal. I think (someone correct me ...) that for the purpose of detecting speed you should be able to use either half of the signal because you're just counting zero-crossings per second, not using the signal to try and track the angle of the sensor in the transmission at any given moment. Really not 100% sure where to go from here though.
 
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