Speedometer error - Where did I go wrong? -UP DATE

[HammaMan]

what's the percent difference on revolutions per mile between the 2 tires? I'd bet that's precisely what the issue was indicating that wheel speed is the source of speed. If gears and tires washed, it'd be in the trans. The fact that tire value alone fixed it seems to confirm the ABS is reporting the speed. Good to know.

Curious what factor the truck knowing what the gearing is in other modules does? Perhaps it's a variable used in calculated shift points / drive modes /etc... Seems like effective gearing would be known simply by RPM/gear/speed and is the only thing of utility? Perhaps holdover variables? Could just be one of those 'we don't know why exactly it needs to be there but it does' type of thing. Used to matter but each gradual part evolvement made it obsolete, but they still do it.

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[ThumperF150]

Well at this point I fully admit the why and where of it all is beyond me. I’m disappointed that changing gears and tires did not keep my speedo accurate but I’m glad there was a simple fix.

But wait, there’s more!

Just found this:


On a 2024 Ford F150, the speedometer gets its signal from the vehicle speed sensor (VSS), which is located on the transmission output shaft; essentially, it reads the rotation speed of the transmission output shaft to determine the vehicle's speed and send that information to the instrument cluster to display on the speedometer.

Key points about the VSS:

• Location: Typically found on the driver's side of the transmission, near the tail housing.
  
  
• Function: Uses magnetic pulses to detect the rotation speed of the output shaft.
  
  
• Electronic signal: The VSS sends an electronic signal to the vehicle's computer which then translates it into a speed reading on the speedometer.

 

[HammaMan]

Dunno where that came from but it sounds like the hallucinations of an LLM

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