Town & Country V6-3.3L VIN R (2003)
Manifold Pressure/Vacuum Sensor: Description and Operation
Fig. 20 Map Sensor - 2.4L
Fig. 21 Map Sensor - 3.3/3.8L
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor or mounts to the intake manifold. The sensor is connects electrically to the PCM.
The MAP serves as a PCM input, using a silicon based sensing unit, to provide data on the manifold vacuum that draws the air/fuel mixture into the
combustion chamber. The PCM requires this information to determine injector pulse width and spark advance. When MAP equals Barometric
pressure, the pulse width will be at maximum.
Also like the cam and crank sensors, a 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold
pressure. The zero pressure reading is 0.5 V and full scale is 4.5 V. For a pressure swing of 0 - 15 psi the voltage changes 4.0 V. The sensor is
supplied a regulated 4.8 to 5.1 volts to operate the sensor. Like the cam and crank sensors ground is provided through the sensor return circuit.
The MAP sensor input is the number one contributor to pulse width. The most important function of the MAP sensor is to determine barometric
pressure. The PCM needs to know if the vehicle is at sea level or is it in Denver at 5000 feet above sea level, because the air density changes with
altitude. It will also help to correct for varying weather conditions. If a hurricane was coming through the pressure would be very, very low or there
could be a real fair weather, high pressure area. This is important because as air pressure changes the barometric pressure changes. Barometric
pressure and altitude have a direct inverse correlation, as altitude goes up barometric goes down.
The first thing that happens as the key is rolled on, before reaching the crank position, the PCM powers up, comes around and looks at the MAP
voltage, and based upon the voltage it sees, it knows the current barometric pressure relative to altitude. Once the engine starts, the PCM looks at the
voltage again, continuously every 12 milliseconds, and compares the current voltage to what it was at key on. The difference between current and
