Where does the speedo pick up its signal?

[Flash1034]

Just out of curiosity, where does the speedometer get its signal from?

thanks,

 

[Wayne M.]

No more cables and little gears in the transmission or transfer case! It's all electronic. The ABS system and/or the powertrain control module sends a message to the instrument cluster, and that's your speed. All of the computers in the truck are linked together similar to your home computer and the USB network connecting the peripherals.

 

[sag2]

It gets it from the wheel speed sensors. It used to be only one sensor, but with the speed of the controllers today they might be averaging all 4 sensors for the spedo. An easy way to check would be disconnect one sensor at a time until the spedo drops out. Just remember the ABS and CEL will probably come on for a while. Most likely would be left front, followed by right front.

 

[Flash1034]

The reason I asked is that last road trip, I noticed the speedo needle fluctuating rapidly 1-2 mph. It only did it for a minute or so then went away.

 

[Wayne M.]

That's a good one. The tach? Sure, but the speedo? I'm not sure.