With modern 4x4s the standard tune-up no longer exists. Sure, you can throw in new spark plugs if you can get to them, and maybe replace the cap and rotor, if the rig has a distributor. But by and large the standard tune and drive has been replaced with fault codes and sensor replacement, which just isn't the same as timing an engine by ear.
What usually tips the driver off to an engine problem is the hideous "check engine" light on the dashboard, or worse yet, the engine icon on the newer rigs. While this indicator could mean that something as simple as the gas cap is loose, the only way to figure it out and fix the rig is to read the codes stored in the vehicle's computer. This used to mean taking the vehicle to the dealer, making an appointment, and letting them hook your baby up to a monstrous machine with various umbilical cords, and then receive a hefty bill for this diagnostic treatment. Not only that, this process only told you what's wrong--fixing it was another appointment and another big bill. Not that we have anything against dealerships or spending money, but there is another way. We picked up an Actron Super AutoScanner, which is very similar to what your regular garage mechanic uses nowadays. Various other brands and models are available, but they all work the same basic way, by reading the codes stored in your vehicle's computer.
However, the Super AutoScanner does more than just read the code; it can also clear the codes and perform other diagnostic tests. By simply plugging the unit into the vehicle's diagnostic port, a few simple keystrokes can confirm that your O2 sensor is dead, or if some other problem has triggered the check engine light. Not only that, the unit can reset the light and allow for many more happy motoring miles.