How does the speed sensor work?

[mabrodis]

Forgive my ignorance if the factory manual has a procedure to testing the speed sensor and therefore telling how it works, I don't have my manual here at work.

I'm curious how the actual speed sensor works, does it output pulses, does it momentarily interrupt the voltage (square-wave?). I think there are two wires going to it, so I would guess one has voltage from the vehicle the sensor would then pulse the other wire as it's turned. Anybody know forsure? I'll drag the ocilliscope out and look at it but kinda wanted to have a idea of what I'm expected to see.

I'm trying to figure out what I need to adjust my speedo, like the Tru-Speed calibrator, only for about $5-$10 in parts and a little processor...

I'll check my factory manual tonight...

Thanks,
Mark Brodis

 

[landtank]

There is actually 3 wires going to it. It outputs a square wave I beleive. You need to be ablt to modulate the frequency to be able to effect a speed change.

Good-Luck

 

[mabrodis]

So the computer counts transitions (edge-triggered), that shouldn't be hard...so said the foolish man..

Thanks..
Mark Brodis

 

[landtank]

Well Mark it wasn't until the second offering from SuperLift that the TrueSpeed actually worked all the time. There was something funcky about the LC that made it eratic until it warmed up in the AM. It was only on the LC and not any other vehicles from what I remember.

 

[RavenTai]

from the FSM

3. INSPECT No.1 VEHICLE SPEED SENSOR
(a) Connect the positive (+) lead from the battery to terminal
1 and the negative (–) lead to terminal 2.
(b) Connect the positive (+) lead from the tester to terminal
3 and the negative (–) lead to terminal 2.
(c) Revolve shaft.
(d) Check that there is voltage changer from approx. 0 V to
11 V or more between terminals 3 and 2.
HINT:
The voltage change should be 4 times per each revolution of
the No. 1 vehicle speed sensor shaft.
If operation is not as specified, replace the sensor.

the EWD shows a transistor in the sensor but not what triggers it, possibly a Hall effect sensor?

if you come up with something please post a recipe

 

[inacoma]

Forgive my ignorance if the factory manual has a procedure to testing the speed sensor and therefore telling how it works, I don't have my manual here at work.

I'm curious how the actual speed sensor works, does it output pulses, does it momentarily interrupt the voltage (square-wave?). I think there are two wires going to it, so I would guess one has voltage from the vehicle the sensor would then pulse the other wire as it's turned. Anybody know forsure? I'll drag the ocilliscope out and look at it but kinda wanted to have a idea of what I'm expected to see.

I'm trying to figure out what I need to adjust my speedo, like the Tru-Speed calibrator, only for about $5-$10 in parts and a little processor...

I'll check my factory manual tonight...

Thanks,
Mark Brodis

Mark, did you ever get this worked out? I was wondering if you could hook up your oscilliscope to the red/orange wire as in christo's instructions here.

basically, I would like to know if we have a pulsed system (square wave) operating at atleast 5v that I could get a signal off of. I don't need to modulate this frequency as I am not needed to change the calibration.

Kumar