Which speed sensors control the speedometer?

Another salvage truck question: For a 2011 4x4, with auto trans, which speed sensor(s) control the speedo/odo? I have a po500 code showing and it won't pass inspection.
Thanks for any help,
Vic

 

Is the Speedometer working?
If so, it’s probably not a speed sensor.

 

No speedometer or odo. A cheap scanning device said "po500, speed sensor A"

 

Is your ABS light on? On the automatic transmission trucks the vehicle speed signal comes from the ABS module to the Combination Meter (instrument cluster) and then the cluster sends the speed signal to the PCM.

 

Not sure on sensor A?
The wheel sensors are code 31,32,33, or 34.

I know the manual transmission uses a separate sensor on the transmission.

 

Sensor A basically means sensor 1 or single sensor as far as the PCM is concerned, the ABS uses one of the rear sensors for the vehicle speed signal output but I'm not sure which one.

 

Someone post which one it was, but can’t remember. It’s been awhile since it was posted. I believe it was Muddinfun, he was pretty versed in this subject.

I’ll see if I can find it later.

 

I was wrong, it was @Jimmyh
It is the right rear.
https://www.tacomaworld.com/threads...-tachometer-often-don’t.677643/#post-23854468

 

I’ve never seen a definitive answer.
But I’ve seen the question asked more than once here. Which one drives the speedometer?

I’m curious if one could jack up the truck and place the truck in neutral and somehow spin a tire fast enough to “know for sure”.

Or is there a better way?

 

Hook up a scan tool and you can view all the speed sensor inputs to the skid control ECU. I don't believe a "single sensor" drives the speedometer, it is what the skid control ECU knows to be the speed, this is taking a speed from all 4.

 

Attached is the best I could find about how Toyota has designed the "black box" of the ABS/skid control ECU. I have to imagine the input sensors being monitored and the speed signal that's being developed is a result of some median voting logic, with a known bad sensor being thrown out of that voting. If for example, you're going down the road and one speed sensor fails or locks up due to ABS actuation, you don't see your speedometer immediately drop off. That is only a best guess at this point because I have not been able to confirm how the SPD signal is actually developed inside the skid ECU. A simple test would be to set yourself up a 4 channel signal generator with an oscilloscope and monitor the output of the SPD signal. Vary the signals generated or disconnect one sensor and see what the resultant SPD signal looks like.