Manifold Pressure/Vacuum Sensor: Description and Operation

LOCATION

Sensor mounted on intake plenum.

PURPOSE

At start-up, the Powertrain Control Module (PCM) uses sensor to read barometric (atmospheric), pressure, for reference, to calculate air/fuel mixture.

During operation the Powertrain Control Module (PCM) monitors sensor input to adjust spark advance and air/fuel mixture.

OPERATION

PCM supplies 5 volt sensor reference voltage.

Sensor, connected to manifold vacuum at throttle body, 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).

OUTPUT VOLTAGES

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.