I had broken my ABS speed sensor on the front passenger side. And I was able to pick one up locally but it was for the drivers side. I noticed now when I was going to install it that the pos/neg on the plugs are opposite of each other. So I don't know if that sensor is a closed loop and polarity doesn't matter. Or if I'm going to have to splice the other connector plug on it?

I'd appreciate any quick help cause I'm trying to change it out as I speak. Thanks!

 

If it helps, the sensor reads resistance in ohms, so I'm assuming that polarity wouldn't matter

 

Only one way to find out

Let us know how it works out

 

lol, alright I put it in and it works!

As I mentioned above I found in the service manual that the sensor measures resistance, so I used my trusty sidekick google to find out that resistance signals do not use polarity, so they can be reversed.

So for anyone with a busted ABS wheel speed sensor, you can replace it with a sensor from any side of the car.

 

So goes the THEROY, but from what I've experienced that's not the case, there have been slight anomalies in my ABS when the old sensor got broken(drivers side front), and the new one came from a passenger side front, and it's got strange pulsing when you go slow, and come to a stop, all of a sudden you can feel the abs... I'm now getting a new drivers side sensor and I'll try and update this post if I find it changed anything, it might have to do with year vintage as I have a '93 and I don't know what year the sensor came from that's on there now, or if the new one was damaged somehow. But from My experience it's not that simple, like anything is on these cars...

 

ABS wheel speed sensors are not resistance based sensors. They are a hall effect sensor, which will produce a small voltage variation as a current is induced by a changing magnetic field.
The toothed wheel produces the varying magnetic field, which in turn will cause the ABS sensor to produce an AC waveform.
Inverting an AC waveform (ie by swapping polarity) in most cases will not cause any issues, as it is essentially a 180 degree phase shift.
However, the design of the toothed wheel may be that it has wider troughs than peaks (or vice versa, or any other way it can vary), in which case the ABS may still work, but may behave oddly.

So, in summary - swapping polarity should not harm the ABS sensor or computer, and in most cases should still work correctly.

If you wanted to be pedantic you could measure the polarity of the other sensors and ensure your new one is the same. If you measure the voltage when moving a metallic object past the sensor in the same direction a forward rotating wheel would travel, and ensure that all sensors produce the same voltage (ie all positive, or all negative). However my knowledge of exactly how the changing magnetic field is detected is a bit rusty, so don't quote me on that last bit.

 

I'll see how it starts feeling as I drive around more, but initially it was just an issue of fitting it and the car recognizing it.

I was going by the service manuals testing of the sensor, which you get the readings from measuring the resistance at the plug, so that's what I was meaning. I didn't pass anything magnetic by it to see the changes, but I did test the drivers side plug, and they were both reading between 1-1.1 ohms, so I guess they're within spec

What I was thinking, is that reversing the polarity might make the ABS think that the wheels are turning in reverse depending on what side you put the sensor on, so idk how that would work or if it matters.

 

Confirming Enervation's explanation of how ABS sensors work.

ABS compares the frequency of the waveform output by the sensors at each wheel to determine their rotational speed relative to each other. If the frequency measured at one wheel differs from the other wheels beyond a pre-determined threshold the system pulses the brake line pressure to that wheel.

 

It in the RX-7 Technical Manual, but I don't have ready access right not. However, if memory serves me correctly when I was wiring the MoTec's Traction Control Module and associate DMC-D, it's just a sine wave output (i.e. Hall Effect as above). Polarity doesn't matter as long as the output is symetric about the zero volts baseline.

Again, please don't bet the children on it as my memory has been know to be fallible