It means that the MAP sensor is not getting the 5 volts from the PCM that it needs to operate correctly. Unplug the wiring harness from the sensor. Connect a voltmeter to the two outside terminals of the plug and then turn the ignition key to the "on" position. If the meter reads about 5 volts, then the problem is in the MAP sensor. BTW, the middle terminal is the one carrying the MAP sensor signal back to the PCM.
If the voltage is not correct, then there is a problem with the the plug or wires or PCM. One of those two outside terminals (I don't know which one) is connected to ground. With the ignition "off", use an ohmmeter and check the resistance between each outside plug terminal and a ground somewhere in the engine compartment. The terminal with zero resistance is the ground terminal and the other is the 5 volt terminal. It's the 5 volt terminal and wire that you have to worry about. If it turns out that neither wire shows zero resistance with respect to ground, then the ground wire and terminal is most likely the problem.
2001 WJ Limited with Quadra-Drive, Kenne Bell Supercharger, 3-inch Kolak exhaust, Stillen rotors (F/R) and MM pads, Addco sway bars (F/R).