ABS or speed sensor question

This was recently talked about here. Basically the speedometer lies. It reads about 2-3 MPH higher than the actual speed with the original tire size. The computer knows the actual speed however so it can correctly record the mileage.

 

All of that has NOTHING to do with the cruise control not holding a rock solid speed.

A cruise speed variance of 3 MPH is NOT considered a problem........with any vehicle.

One designed for high fuel efficiency in particular tends to be slower to correct a speed variance.

Why are you worried about it ??
If your model has an ECO mode button......turn it OFF and the cruise might hold tighter, if that is REALLY a big concern.

 

I'm pretty sure it starts with the four wheel sensors. The New Car Features manual describes how the speed gets to the combination meter, which has a bit of the Rube Goldberg to it. The skid ECU gets the readings from all four wheel sensors. It then generates a pulse signal where the speed of the pulses represents the vehicle speed, and the combo meter reads that (as does the nav ECU, etc.)

It seems that pulse signal has a longer history as a way of carrying speed information, and might have come straight from a transmission sensor in some older model, but now it just comes from the skid ECU synthesizing a compatible signal.

You can put the skid ECU into a wheel-sensor test mode, which is more sensitive than normal driving. You enter the test mode and do some specified maneuvers in the manual, ending in driving in a straight line for a certain distance and speed (so you have to pick a starting place where you can do that), and then it tells you if any of the wheel sensors are iffy.

That's supposed to be done any time a wheel bearing or sensor is replaced, to confirm the repair, though not everyone does.