BARO / MAP Sensor Switching Valve: Description and Operation

MAP Sensor Vacuum Switching Valve:

To alternate MAP sensor readings between intake manifold pressure and atmospheric pressure, the system utilizes an ECM-controlled vacuum switching valve (VSV). To switch the input signal to atmospheric pressure, the ECM energizes the VSV for about one second under these conditions:

1. When the ECM is reset.

2. When these three conditions exist simultaneously:

a. Engine speed is less than 200 rpm.
b. Battery voltage is more than 9.5V.
c. Vehicle speed is less than 1 km/h.

3. When the ECM judges a high altitude condition, it takes an atmospheric pressure reading and sets its "barometric map." High altitude is indicated when the MAP sensor signal indicates less than 596 mmHg absolute pressure.