Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor Location:

LOCATION

Sensor is mounted on firewall and connected to manifold vacuum at the throttle body.

PURPOSE

Engine controller uses input to adjust spark advance and air/fuel mixture.
Manifold absolute pressure and voltage to engine controller are directly proportional (manifold absolute pressure increases, low vacuum, voltage to engine controller increases and vice versa).

Manifold absolute pressure and voltage to engine controller are directly proportional (manifold absolute pressure increases, low vacuum, voltage to engine controller increases and vice versa).


OPERATION

Engine controller supplies 5 volt sensor reference voltage. Sensor converts intake manifold pressure into voltage.

THEORY

Sensor resistance and manifold absolute pressure are inversely proportional (as manifold absolute pressure increases, (low vacuum), sensor resistance decreases and vice versa).

TYPICAL READINGS

Sensor output voltage range is 0.5 to 4.5 volts.

Output voltages between 0.5 and 1.5 volts indicate a high vacuum situation, such as idle or deceleration.

Output voltages between 1.5 and 3.0 volts indicate a medium level of vacuum such as a cruise or slight acceleration condition.

Output voltages between 3.0 and 4.5 volts indicate a low vacuum situation such as hard acceleration or a mechanical failure.

Any reading of 0 volts or over 5 volts indicates a problem.