Abstract: A manifold absolute pressure (MAP) sensor emulator is used to emulate the operation of a properly functioning MAP sensor of the type under test. The test involves breaking the pneumatic connection between the vacuum hose from the intake manifold and the MAP sensor input, and breaking the electrical connection between the MAP sensor output and the vehicle on-board computer. The vacuum hose is instead connected to a vacuum probe input of the emulator and the electrical connection to the on-board computer is also connected to the emulator. Thus, the emulator is connected in place of the MAP sensor, and software in the emulator is programmed to provide a voltage or frequency output corresponding to various vacuum levels of a particular MAP sensor. Thus, the emulator can emulate the sensor and, if the engine operates properly in this mode, it indicates that the MAP sensor was bad, and, if not, it indicates that the problem may be elsewhere.