Speedometer not working, where to begin

[HappyFrog]

My speedometer has been out of order for the last couple of months and I started debugging on it during the weekend. Nothing seems out of the ordinary, plugs are all well connected, wires seem healthy and no fuses burnt. RPMs works fine btw.

The transmission is a 6mt from an 06 impreza and the instrument cluster is an electrical stock one. There are two speed sensors on the gearbox, one on the front and one on the rear somewhere, can't really see where it goes. Are both used for the speedo or is only one of them (and which one then)? Is there a way to measure if the sensors give proper feedback?

Any help or ideas are appreciated.

[Legacy777]

Did your speedometer work prior to installing the 6spd?

You should only need one speed sensor input to speedometer, and that's likely going to be the front one. The rear speed sensor is likely used for the DCCD controller. If so, are you or are you planning to run a DCCD controller? If not, your center diff is basically an open diff without a controller.....assuming you have a DCCD trans.

If you've got the front speedsensor wired up and it still doesn't work, you should verify the gear inside the trans is turning, if it is, it's possible the output signal from the speed sensor is different on the newer trans vs. the older trans.

[HappyFrog]

I did not convert it and yes it has worked. I haven't touched anything that should have anything to do with the speedo so it almost has to be a bad connection. It is a dccd box without the controller, so i'll try to follow the wiring of the front sensor first and see where it takes me.

[HappyFrog]

The sensor appears to return the rpm signal, it showed 110 ohm at startup and fell to 72 ohm when the rpms dropped also revving it changed the resistance. The sensor only has this lead and 12v connected to it, so there must be another one telling it what gear is selected or am I following the wrong sensor?

[HappyFrog]

Alright, just been told that measuring resistance makes no sense on this sensor, but I may have an idea of what could be wrong.

[Legacy777]

Well keep us posted on what you find out.

[HappyFrog]

It appears that there no signal from the speed sensor. I found a lot of bad wire splicing while going through the wiring, so will try to redo some of them before writing off the sensor.

[HappyFrog]

It turned out to be a bad wire under the dash running from ecu to instrument cluster - was fixed last weekend by the tuner, took him less than an hour to figure out... sometimes it is just easier to ask