R32 GTR Speedometer Wiring and Plugs

[nouveau_poor]

So I'm trying to track down the reason why my vehicle speed sensor isn't sending signal to the ECU. This all stems from my HICAS light coming on after driving for a while, and the heavier steering that comes with it. I've already ruled out or fixed the typical causes like speedometer cable issues, steering wheel alignment, and power steering fluid. I know for a fact that it works because I can test the functionality using the "simulate drive" function in the Nissan Data Scan tool

So long story short, I think I've narrowed down the cause of the light: When I plug my computer into the OBD port for Nissan Data Scan use, and drive around a bit, all the readings function as they should save for one, the vehicle speed reading. It shows zero regardless of actual vehicle speed and does not move at all despite the speedometer cluster operating as it should. This leads me to believe that the speed signal is not reaching the ECU as it should. My guess is that the vehicle speed sensor in the back of the speedometer unit must be faulty. A more concerning possibility is that the speed sensor wire from the ECU to the speedometer is bad/broken. From the glance that I took of the ECU, wire 53 has not been cut/tampered with. 

From my understanding reading various threads, wire 53 goes into the back of the speedometer via those square plugs for the speed signal and the part of the ribbon cable/printed circuit that goes inside of the back of the speed meter assembly (early model, yellow, 1990) is the bit of cable that connects to the speed sensor. Shown in picture. Tracing the circuits that come out of this section of cable leads to the middle speedometer plug.

My question is, which speedometer plug pin corresponds to wire 53 on the ECU? I'd like to test for continuity with a multimeter to verify that the wire is good before whipping the wallet out to buy and try a new speedometer cluster. Does anyone know from experience or have a different pin diagram? In the service manual, the only mention I've found of the VSS just says to check wire 53, and the pinout diagram of the speedometer cluster in the manual has no mention of the speed sensor. Shown below. Unfortunately, I can't guess based off of the green/yellow wire color on mine as the wire colors are obscured up to the plug. 

 The picture of the back of the speedo is not of mine, and it's hard to make out which wire goes where. Just added for reference (Other note, according to the pin diagram below, there should be a wire for pin 15, but the plug in the photo shows no wire going into that slot?)

 

[nouveau_poor]

Poked around a bit more in the service manual (slow day) and found this section under wire diagrams for "W-1 4WD Vehicles (RB20DET/RB26DETT equipped models)". This diagram and pinout is slightly different than the one shown in the speedometer wiring section posted previously. The one posted previously seems to correspond to the wiring diagram shown in "C-1 4WD Vehicles (RB20DET/RB26DETT equipped models)". 

This does explain the note about pin 15 not being in the photo, which matches the W-1 diagram below. Apparantly that circle with the squiggle in it connected to pin 13 and 14 is the vehicle speed sensor. Makes sense because you can see both of these pins connecting to circuits that trace into where the sensor is.  

Would it be accurate to say that one of these pins is connected to wire 53?

What about the other pin connected to the VSS? If one is for wire 53, what wire is the other pin for and what does it do? I'd assume id have to check both for continuity. 

What is the difference between C-1 and W-1 and what does it mean? 

A lot of oddities today.

[GTSBoy]

Just bell out all the pins. If one of them squeaks, it's continuous. If none of them squeak, you have a problem. Then you really do need to know which is which.

Of the 2 wires on the back of the cluster - logically, if one goes to the ECU, the other is probably power or earth, no?

[nouveau_poor]

Update on this: Was testing continuity based on the pinouts above and my multimeter was beeping normally. GTSBoy was right, the other wire 14 seems to be linked to the cars ignition. 

While I had the speedo out I figured I'd take the meter itself out to test the wires of the speed sensor, or at least look at its condition. Turns out, I probably found the answer to my issue since the Kakimoto speedo that the previous owner put in seems to be from a late model meter. There is no sensor that the ribbon cable connects to like it's supposed to (last photo), therefore no signal. Maybe the previous owner didnt mind the heavy steering and just wanted the increased speed reading, but I'll see to getting a proper meter. Hopefully this is the fix that finally resolves this. 

[nouveau_poor]

Pleased to say that my hunch was correct. I picked up a Nismo 320km speedo for a reasonable price and confirmed that it had the speed sensor in there before putting everything back together. Tested again with Nissan Data Scan and finally got a functional ECU speed reading for the first time! Drove down to my local hardware store for a few things and NO MORE HICAS LIGHT! Hope these posts help someone else down the line.

To be honest, I think I'll probably get a HICAS eliminator kit down the line but for now at least I can enjoy the thought of my car with a working unit and the "spirit" of one of the GTRs main features.

[Rb25orange]

Sorry for digging in a old thread,

but in the end was it the pin13 behind the dash cluster that goes to pin53 at the ecu ?

I am having exactly the same issue.

would like to gain some knowledge before I crack down with the multi.

Cheers.

 

[nouveau_poor]

The issue in the end was that the speedometer itself, the one with the mileage counter, that was fitted was meant for a late model cluster, rather than the early model needed for my 1990. Essentially, the cable from the ECU that connects to the speedo had nothing to connect to or read, hence no speed reading and resulting in the HICAS light. The continuity from the ECU to the speedo plug came back fine, no wire degradation. From what I remember, I think the actual speed sensor wire was green and yellow if that helps.

Early model speedos have this extra wiring bit: