Manifold Pressure/Vacuum Sensor: Description and Operation

Fig. 1 Manifold Absolute Pressure (MAP) Sensor Location:

MAP Sensor Location:

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 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.

NOTE: The following information is intended to be used in conjunction with the electrical diagrams.

CIRCUIT OPERATION
From the Powertrain Control Module (PCM), circuit K6 supplies 5 volts to the Manifold Absolute Pressure (MAP) sensor. Circuit K6 connects to cavity 6 of the PCM.

Circuit K1 delivers the MAP signal to the PCM. Circuit K1 connects to cavity 1 of the PCM.

The PCM provides a ground for the MAP sensor signal (circuit K1) through circuit K4. Circuit K4 connects to cavity 4 of the PCM.