Dodge Ram Truck 1500-2500-3500. Manual — part 1471

SENSOR-MAP

DESCRIPTION

3.7L V-6

The Manifold Absolute Pressure (MAP) sensor (2) is
mounted into the front of the intake manifold with 2
screws.

4.7L V-8

The Manifold Absolute Pressure (MAP) sensor (1) is
mounted into the front of the intake manifold with 2
screws.

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5.7L V-8

The Manifold Absolute Pressure (MAP) sensor is
mounted to the front of the intake manifold air plenum
box.

8.3L - SRT-10

The MAP sensor (2) mounts to the drivers side intake
manifold plenum.

OPERATION

The MAP sensor is used as an input to the Powertrain Control Module (PCM). It contains 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 manifold absolute pressure
(MAP) equals Barometric pressure, the pulse width will be at maximum.

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 0.5V and full scale is 4.5V. For a pressure swing of 0–15 psi, the voltage changes
4.0V. To operate the sensor, it is supplied a regulated 4.8 to 5.1 volts. Ground is provided through the low-noise,
sensor return circuit at the PCM.

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The MAP sensor input is the number one contributor to fuel injector 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 at a
higher altitude, because the air density changes with altitude. It will also help to correct for varying barometric pres-
sure. Barometric pressure and altitude have a direct inverse correlation; as altitude goes up, barometric goes down.
At key-on, the PCM powers up and looks at 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
voltage and what it was at key-on, is manifold vacuum.

During key-on (engine not running) the sensor reads (updates) barometric pressure. A normal range can be
obtained by monitoring a known good sensor.

As the altitude increases, the air becomes thinner (less oxygen). If a vehicle is started and driven to a very different
altitude than where it was at key-on, the barometric pressure needs to be updated. Any time the PCM sees Wide
Open Throttle (WOT), based upon Throttle Position Sensor (TPS) angle and RPM, it will update barometric pressure
in the MAP memory cell. With periodic updates, the PCM can make its calculations more effectively.

The PCM uses the MAP sensor input to aid in calculating the following:

•

Manifold pressure

•

Barometric pressure

•

Engine load

•

Injector pulse-width

•

Spark-advance programs

•

Shift-point strategies (certain automatic transmissions only)

•

Idle speed

•

Decel fuel shutoff

The MAP sensor signal is provided from a single piezoresistive element located in the center of a diaphragm. The
element and diaphragm are both made of silicone. As manifold pressure changes, the diaphragm moves causing
the element to deflect, which stresses the silicone. When silicone is exposed to stress, its resistance changes. As
manifold vacuum increases, the MAP sensor input voltage decreases proportionally. The sensor also contains elec-
tronics that condition the signal and provide temperature compensation.

The PCM recognizes a decrease in manifold pressure by monitoring a decrease in voltage from the reading stored
in the barometric pressure memory cell. The MAP sensor is a linear sensor; meaning as pressure changes, voltage
changes proportionately. The range of voltage output from the sensor is usually between 4.6 volts at sea level to as
low as 0.3 volts at 26 in. of Hg. Barometric pressure is the pressure exerted by the atmosphere upon an object. At
sea level on a standard day, no storm, barometric pressure is approximately 29.92 in Hg. For every 100 feet of
altitude, barometric pressure drops 0.10 in. Hg. If a storm goes through, it can change barometric pressure from
what should be present for that altitude. You should know what the average pressure and corresponding barometric
pressure is for your area.

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REMOVAL

3.7L V-6

The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold

An o-ring (2) is used to seal the sensor to the intake
manifold.

1. Disconnect electrical connector at sensor.

2. Clean area around MAP sensor.

3. Remove 2 sensor mounting screws.

4. Remove MAP sensor from intake manifold.

5. Check condition of sensor o-ring.

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