Q: I have a ’93 Jeep Grand Cherokee whose cruise control has completely stopped working. Any idea what the problem might be?
A: Cruise control has gone through so many different iterations over the years, it’s almost comical. At the beginning it was purely mechanical, then it was vacuumactuated, then it was electromechanical, and now the state of the art is to control the electronic throttle body directly. Your version is electromechanical, which means that the throttle pedal is directly connected to the throttle body through a cable, and the cruise control is achieved by way of a servomotor that sucks in that cable and holds it in place. All cruise-control systems are mandated to use designs that don’t interfere with throttle control when they fail, which is what yours has done. The question then becomes, what is the root cause? There are two cheap potential fixes to look at first.
Since cruise is operated by electrical switches, it’s possible the contacts have worn out or become corroded. Taking those apart for inspection and cleaning eliminates that possibility. You should also check the fuses related to the system and, if you have a multimeter, check that the wiring from the fuse box to the module is intact. (Set it to measure resistance: if there’s a reading, the line is good; if there’s no reading, the wire may be broken.)
Now, about the expensive fix. Cruise-control modules from this era are not known for their long-term durability. Usually you’ll see failure in the module’s electronics, the plastic gears, the motor, or the various mechatronic contrivances that make these contraptions work. Complicating matters, these are neither cheap nor easy to replace. At a dealership, you’d be staring down a huge repair bill. If cost is an issue, and considering the age of the vehicle, it might make more sense to just use the pedal the old-fashioned way and live with it.