Parts are expensive on today's cars. Some electrical parts like modules or fuel pump assemblies can cost as mush as $600.00 and labor to install can cost $200.00 or more. We always say "Don't Guess, Do The Test" ...Testing eliminates the old fashioned idea of making an educated guess about what is wrong with your car or light truck.
Testing has 2 objectives...to determine which parts are defective and what caused the parts to fail. Here is an example of how testing finds the defective part and what caused the part to fail, along with saving you money in the long run.
EXAMPLE: Your vehicle stall and testing shows a defective idle motor. The second phase of the test reveals a misfire from worn out plug wires which causes the computer to make the idle motor adjust more often because of the misfiring plug wires.
In this case, your vehicle has two problems and replacing the idle motor alone will only temporarily cure your problem, because the new motor will fail again because of the ignition problem. TESTING SAVES YOU MONEY!