Just to preface this, this is my project https://www.rx8club.com/general-automotive-49/renesis-powered-homemade-locost-198067/

Now my problem, the speedometer doesn't work. I tested the vehicle speed sensor and it is fine. Tested the connection from the VSS to the transmission control module and it is fine. Tested every input and output on the TCM and it is all fine. All functions from the tcm to the gauges work fine, gear select, manual mode, backup light, etc. The gauges work fine, warning lights, tachometer, even the odometer works, just not the speedometer.

In order to get a VIN and pass inspection I need to have a working speedometer. Has anyone ever heard of this problem or know of a solution? I've traced it as far as I can, which is to the CAN system output from the TCM to the ECU.

Has anyone ever tried putting an aftermarket speedometer in their car? Should just be able to tap into the VSS right?

 

Some here are far more knowledgeable than I in this regard but I think the readings are dependant on ABS sensors.

Paul.

 

Hmmm that kinda makes sense, so it can calculate your actual speed if you have wheel spin, and without that input the PCM can't calculate and just never sends anything but 0 to the speedometer.

Would someone be willing to pull their ABS/DSC and the DSC fuses to see if their speedometer stops working to confirm this before I spend 20 or so hours pulling my wireing harness apart again and hooking up the wheel speed sensors?

 

Try to use scan gauge II for speedo.

It clocks time so it should calculate speed off distance traveled.

I keep my scan gauge in front of the cars speedo which I never see.

 

I'm not certain that it does use the ABS sensors to read speed. From what I can tell, most (if not all) the cars have a error in the speed reading. The speedometer reads too high, even with OEM tires. I believe the speed is read off the ecu and uses engine rpm to calculate the ground speed.

 

It's not that the speedo is off a little, it doesn't work at all, it just sits at 0mph no matter how fast I'm going. My OBD/CAN reader's live data is showing 0mph as well, so the scan gauge wouldn't work either.

 

You were right, the speedo signal depends on the ABS. I went to my local mazda dealer and asked pretty much what I asked here and told them your suggestion, they said that doesn't even make any sense and that the speedometer would work fine without the abs hooked up, and said to check the turbine sensor as well as the vss because the speedo gets its signal from both of those. But I check and they are both fine. Asked over on 2carpros.com and a tech there confirmed what you said, that the speedo definitely gets its signal from the abs sensors. So I hooked up the wheel speed sensors and now my speedometer works. Now I know to take everything the mazda dealer says with a grain of salt...