2005 Mazda RX8



July, 7, 2010 AT 6:53 AM

Electrical problem
2005 Mazda RX8 Two Wheel Drive Automatic 72,000 miles

Ok, so, the setup. I'm building a car with the drivetrain from an 05 rx8 automatic.

I'm using the rx8 gauges and my speedometer isn't working, it just reads 0mph no matter what speed I am at. My OBD/CAN reader shows 0mph in the live data section as well. Everything else transmission related and gauge related works, tach, oil pressure, temperature, transmission range lights, even the manual shift mode, just not the speedo.

I checked the VSS by first makeing sure there wasn't a break in the signal wire by doing a continuity test between the sensor and the transmission control module. I then hooked my multimeter up to the VSS and as I rolled the car slowly it would cycle between 0.5v and 12v. Can't trace it any farther than that because it sends the signal to the PCM over the CAN system.

I then performed the same test for the Turbine Sensor. Continuity was fine. Because the turbine sensor cycles 10x faster than the VSS and because I have less control of the speed the multimeter test was not very conclusive. It would sometimes sit at 0.5v, it would occassionaly go up to 13v for a split second, but most of the time it would hover right around 6.5v. So I can't tell if it is malfunctioning or if my multimeter is averageing out the 0.5v and +-12v becaue the signals are coming in so quickly. I don't have access to an oscilliscope.

I've have quite a bit of varying opinions on what the problem could be... I have the abs system disabled and some people say the speedometer doesn't work because of that, while others say the abs system only makes slight changes to the speedo reading and wouldn't stop it from working all together. Some people say the speedometer signal comes from the turbine sensor not the vss. Some people says it comes from both and it won't work unless they both work.

Any clarification on where the speedometer actually gets its signal would be helpful.

Are there any other tests I can/should perform on the two sensors?

Is there any other way to test the turbine sensor without an oscilliscope?

Do you think that the sensors are even the problem?




5 Answers



July, 7, 2010 AT 11:20 AM

Hi Daed,

Thank you for the donation.

The VSS is only for the PCM operations to understand the vehicle apeed and change gears accordingly.

Speedometer is driven by signals from the ABS Hydraulic Unit Control Module.
Since you have disabled the ABS, the speedometer would not work.



July, 7, 2010 AT 11:33 AM

Thanks, I'll hook up the abs then and see if that works. I used the abs block and controller and have all the sensors still in the wheel hubs, so I just need to run and reconnect wires, should only take me a day or so. Will let you know if that solves the issue.



July, 7, 2010 AT 11:41 AM

Will be waiting for the results. Good luck.



July, 7, 2010 AT 8:52 PM

Hooked up the abs sensors and the speedometer works! You are the man! : )

Thanks a lot!



July, 8, 2010 AT 8:53 AM

Cheers, glad to know the problem is fixed.

Thank you for the feedback and have a nice day.

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