Sounds like the speed sensor, which is usually located in the year drive axle. It is easily replaceable with only one little bolt holding it in. It's a little magnet type thing that detects the revolutions of the rear axle and thus tells you how fast you're going and how many miles, and I think even stops your cruise control from working when it goes bad. Sometimes it gets little bits of metal stuck to it (since its a magnet) and stops it from working. In this case you can sometimes just take it out and clean it. On your Rodeo it should have also made your engine light come on, in which case the computer diagnostic will read a code telling you it's the speed sensor. Auto Zone, and probably others, will read your engine light codes for free, by the way, so it doesn't hurt to check if this is also the case. .