No wheel speed all of a sudden?

[Blakeo]

1996 R33 Skyline GTS25T, NON ABS MODEL. 

Up till a couple months ago ecu was displaying wheel speed well. For some reason now it is no longer showing it. Only thing I have touched wiring wise is cutting a wire for the hicas ecu which puts the hicas light on the dash after installing a delete kit. 

Wheel speed still works on the dash, but my boost by gear etc no longer works due to ecu not seeing wheel speed. 

I am going to try and reconnect this wire tomorrow and see if it fixes the issue. 

The Yellow/Green wire on the ecu is for Vehicle speed and probing it with a multimeter in ac or dc mode, it does not give a reading. 

Any ideas? 

Edited April 19, 2021 by Blakeo

[GTSBoy]

So, we're not talking about wheel speed here. VSS is on the gearbox, not a wheel.

The VSS sends an AC signal to the speedo head, where it is converted to a PWM (square wave) 0-5V signal that the ECU, HICAS, TCU, etc all read on the vehicle bus.

If you want to measure the presence of that signal at the ECU it is best done with a scope of some sort, rather than a multimeter, as you won't reliably see it with a meter.

The speedo head might be faulty.

[Blakeo]

1 hour ago, GTSBoy said:

So, we're not talking about wheel speed here. VSS is on the gearbox, not a wheel.

The VSS sends an AC signal to the speedo head, where it is converted to a PWM (square wave) 0-5V signal that the ECU, HICAS, TCU, etc all read on the vehicle bus.

If you want to measure the presence of that signal at the ECU it is best done with a scope of some sort, rather than a multimeter, as you won't reliably see it with a meter.

The speedo head might be faulty.

Hm ok, I don't have a scope. Is that something an auto electrician can sort out? 

When you mean the speedo head has a fault, but wouldn't the dash not be working then because both take inputs from the same sensor on the gearbox? I think I can role out a fault with the sensor on the gearbox? 

Waiting to hear back from Link support too, wondering if it could be an ECU issue. 

[GTSBoy]

5 minutes ago, Blakeo said:

When you mean the speedo head has a fault, but wouldn't the dash not be working then because both take inputs from the same sensor on the gearbox?

There is circuitry to take the AC signal from the sender and make the needle move. That appears to be working. There is other circuitry that takes the AC signal from the sender and transmits it as the PWM signal on the bis. That could be borked. It happens.

[Blakeo]

On 4/19/2021 at 2:36 PM, GTSBoy said:

There is circuitry to take the AC signal from the sender and make the needle move. That appears to be working. There is other circuitry that takes the AC signal from the sender and transmits it as the PWM signal on the bis. That could be borked. It happens.

Where abouts would that circuitry be? There's four wires coming off the back of this VSS on the gearbox. 

1 I have traced back to the cluster (the circuitry to convert it to dc for the needle, must be built into the dash cluster?) 

The green/white wire, I have traced goes over the gearbox under the back of the motor and ties into the ecu harness. From there I lose it, because otherwise I will need to strip the harness down. 

But I believe your right, because this green/white wire is not the same color as the one at Pin 29. 

Any ideas, I'm lost and most auto electricians near me are booked out a month in advance atm. 

[GTSBoy]

1 minute ago, Blakeo said:

Where abouts would that circuitry be?

In the speedo head. It's all in the speedo head.

[Blakeo]

Just now, GTSBoy said:

In the speedo head. It's all in the speedo head.

When I search speedo head on google, its coming up with photos of the dash cluster. Is that where you mean mate? 

[robbo_rb180]

so Speedo works on the dash but ecu doesn't detect non-driven wheel speed?
What ecu? probably using one of the abs sensors for non-driven speed and you have now modified the circuit as some ecu require a digital input not Ac as most abs sensors are.

what happens when you reconnect the wire you cut?

[Blakeo]

23 minutes ago, robbo_rb180 said:

so Speedo works on the dash but ecu doesn't detect non-driven wheel speed?
What ecu? probably using one of the abs sensors for non-driven speed and you have now modified the circuit as some ecu require a digital input not Ac as most abs sensors are.

what happens when you reconnect the wire you cut?

Hi Robbo, 

As per my original post mate the car is a Non-ABS model. The vehicle speed comes from the gearbox. This is shared to both the dash and ecu. 

No difference, the wire I cut was for the HICAS warning light after reconnecting the warning light come back on the dash but still ECU doesn't pickup wheel speed as it did before. 

I am using a Link G4+ ECU, Link support has been very good and we have narrowed down the issue to be wiring but due to my inexperience I can't trace where that green/white wire goes. Currently considering a new old stock wiring harness my local Nissan dealer has in stock.. 

[robbo_rb180]

It's in the loom between the dash and ecu. There is a plug that won't be seated properly as has been mentioned the dash does the conversion from the speed sensor then a wire goes to a connector near the ecu. 

No need for a new old stock loom. Find the plug and check it or remove the cluster find output pin and run a new wire to the ecu. 

I'll try and get a picture of the connector in the morning 

[robbo_rb180]

Have had issues in the past with Rb to s chassis conversion wiring with the that dash output not connected and speed needs to be connected for things to work correctly. 

 

Pin 53 is speedo input on Rb25 ecu

Double check connectors here and back of the cluster. 

Edited April 21, 2021 by robbo_rb180
Add info

[Blakeo]

1 hour ago, robbo_rb180 said:

Have had issues in the past with Rb to s chassis conversion wiring with the that dash output not connected and speed needs to be connected for things to work correctly. 

 

Pin 53 is speedo input on Rb25 ecu

Double check connectors here and back of the cluster. 

Hey mate, I've just pulled the cluster out of my car, but can't find any connects like that behind it? 

I've had a search around the ecu in the passenger side kick panel and can't find it either. I'm starting to feel really stupid - Or I am hoping I don't need to take the whole dash out to access that plug? 

[GTSBoy]

9 hours ago, Blakeo said:

Hey mate, I've just pulled the cluster out of my car, but can't find any connects like that behind it? 

The connector in the photo is on the other side of the car. See the heater fan blower housing in the photo?

[Blakeo]

Issue sorted, I ended up having to pull the whole dash out of my car and replacing the heater core. 

Heater core must've exploded or been leaking for a bit. Soaked those connectors in question with coolant, took it all apart cleaned it out with contact cleaner. Replaced the heater core made sure it doesn't leak and put it all back together and have my speed signal back.  

Replace those heater cores guys, they're getting too old now lol. 

[robbo_rb180]

Good to hear you got it sorted. 

[Blakeo]

On 4/24/2021 at 8:17 PM, robbo_rb180 said:

Good to hear you got it sorted. 

Thanks mate, really appreciate your help your suggestion lead straight to the cause.