mx5cartalk.com

Here one for the electronically minded people.

About a year ago my VSS (Vehicle speed sensor) died. Its a common issue when the solder on the terminals crack and loose connection. I fix it by resoldering mine way back then and has been perfect till now.
I popped mine out last night and had a look. The soldering job I did was fine, but still unsoldered it all to check, and about 1cm back up the cable it looked like this: (rusty cable hanging on by a thread)


I cut and stripped the wire back to clean cable and resoldered, went for a drive, but still no speedo. (and got error PO500 VSS)
Today I hooked the end up to a drill and a volt meter (measuring ACV) and slowly upped the speed.



At the drills top speed it showed about 14v (jumped between 12 and 14.something)
Does this sound right?

Is the sensor fine? I assume on a 12V car system, the sensor isn't going to generate a voltage higher than say 15v??

Should I reconnect it all and start looking elsewhere for the problem? Maybe something in the cluster?

The sensor should be sending out a pulse (square wave), it is the duration of the pulse that you are trying to measure. I'm not sure if your multimeter can measure the pulse. Does it have an RPM feature? Do you have an osciliscope?

No don't have an oscilloscope

I googled and read it outputs a wave, but you can measure what AC volts it's outputting (but no one mentions what that value should be.
If I turn the drill slowly it measures around 1v and then increases as the drill speed increases.
Measuring the wave would be best but don't have the equipment.

I'm buying a volt meter this afternoon (using works old dodgy looking one here), should I get one with an rpm reading on it? Would that work?
I assume an oscilloscope would be expensive?

Oscilloscope cost around $500 for a 2 channel (non usb type). If you are in Brisbane I have one.

Most multimeters these days will do RPM, just read the box.

wow $500, thats only 'just' a bit more than buying the sensor new from Mazda
Will buy a decent multimeter this arvo and try the sensor in the car, see if it works, if not i'v got a friend who's letting me swap the sensor out of her MX-5 into mine, which will tell me straight away if its the sensor or not.

Supercheap $60 (http://www.supercheapauto.com.au/online-store/products/SCA-Multimeter-Digital-Automotive.aspx?pid=156452#Cross)

•DC/AC voltage, DC amps, resistance, diodes & continuity testing, dwell, tachometer & data hold

Jaycar $60 (http://www.jaycar.com.au/productView.asp?ID=QM1444)
This has an inductive pickup for RPM so I'm not sure if it will pickup a square wave tachometer signal, you could always ask.

Ok so swapped my sensor into another 6speed NB, no speedo. Nothing.
Swapped the original back in. Speedo works.
So my VSS is definitely dead.
Must be something inside the casing has come loose or failed.
I can't see how it comes apart at all, nor is there anything I can find on the net about pulling it down to repair.

Oh well, on the lookout for a second hand one now