2005 Kia Spectra Speedometer/Odometer/cruise control stops working when the car warms up

On your odometer and cruse control, there is a Input Shaft Speed Sensor, or a Output Shaft Speed Sensor, depending on if it is a automatic or manual trany, that probably are bad on the transmission. Each part is an external part and around $40 so wouldn't be too much to repair.

The Speed sensor is the simple answer and in the case of the Kia usually completely wrong. If you look at the forums we all mention when our car gets warmed up, but more critically when it's hot weather outside, the speedometer but quits working really fast, if you keep driving your transmission will start hard shifting. If you run your air conditioner, it happens even faster. If it's cold outside it takes along time for Speedometer to quit. I have changed my speed sensors three times it makes no difference. Don't bother with this. I have come across only two answers that might help. 1. it's a problem in the cluster wiring or plugs at the cluster. 2. It's the Diode on the Alternator going bad and generating and AC (alternating current )wave that confuses the speed sensors on the transmission. At first I couldn't figure out how this could relate to outside temp. Then I realized, that's when you turn on your air conditioner, this puts a load on the Alternator, causing it to heat up faster and generate the (AC)Alternating current wave. When it's cold outside you have to drive longer to heat up the alternator enough to cause this problem. So I am going to change my alternator next. Hope this works because it's not the speed sensors. If your speed sensors are bad, I've been told the just don't work. The speed sensors are not subject to outside temps cause it's much hotter in the transmission than it is outside anyway. It's a borderline Alternator, that works well enough to operate the car but when warms up generates and Alternating current wave that messes up speed sensors.