Manifold Pressure/Vacuum Sensor: Description and Operation

Wiring Diagram:

DESCRIPTION
The MAP sensor measures the changes in the intake manifold pressure which result from engine load and speed changes. The sensor converts the pressure input to a voltage output signal.

OPERATION
The ECM/PCM provides the MAP sensor with a five-volt reference voltage, a bias voltage, and a ground. The sensor output signal is scaled by the bias voltage.

Manifold Absolute Pressure (MAP) is the opposite of manifold vacuum. When manifold pressure is high, vacuum is low.

The MAP sensor is also used to calculate barometric pressure under certain conditions. This eliminates the need for a separate sensor.

As the manifold pressure changes, the electrical output of the sensor also changes. A higher pressure, low vacuum (high voltage) requires more fuel while a lower pressure, higher vacuum (low voltage) requires less fuel. By monitoring the sensor output voltage, the ECM/PCM determines the manifold pressure and can increase or decrease the "ON" time (or pulse width) of the injectors to allow for the addition or reduction of fuel required.

The ECM/PCM also uses the MAP sensor to control ignition timing.

Legend

1. Crankshaft Position Sensor
2. Engine Coolant Temperature (ECT) Sensor
3. Intake Air Temperature (IAT) Sensor
4. Manifold Absolute Pressure (MAP) Sensor
5. Engine Control Module (ECM) / Powertrain Control Module (PCM)
6. Circuit Opening Relay
7. EFI-HTR Relay
8. Heated Oxygen Sensor 2(HO2S 2)
9. Oxygen Sensor (O2S)