I would really like to have a look at the diagram for the odometer and speedometer wiring for my 2015 RAV4 LE. I expect that there will be some kind of Hall effect or optical sensor on the output shaft feeding both the odometer and speedometer.
I would like to find out if the pulses from the sensor go into the ECU and through CAN bus to the speedometer, or if the sensor feeds the odometer and speedometer directly.
I need to do more testing, but it looks like my new speedometer is reading about 6.5% too high, and the Toyota service guy says that's inside their "don't care" zone. On a nine-mile highway test, my odometer was about 3% high.
It would be great if the dealer would calibrate the speedometer, but I may have to fix it myself. My tentative fix is to put a small 8-pin microcontroller between the sensor and the speedometer, get the microseconds between input pulses, add 6.5% and send new pulses to the speedometer. This obviously depends on just how these work, so I have to gather information first.
Any information appreciated! Thanks.