The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at wide open throttle.
A scantool displays manifold pressure in volts. Low pressure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.
If the MAP sensor fails the ECM will substitute a fixed MAP value and use the throttle position sensor (TPS) to control fuel delivery.
Code 33 will set when:
An open in CKT 469 or the connection will result in a Code 33.
Ignition "ON", engine "OFF". Voltages should be within the values in this chart:
Altitude | Voltage range |
below 305 | 3.8 - 5.5V |
305 - 610 | 3.6 - 5.3V |
610 - 914 | 3.5 - 5.1V |
814 - 1219 | 3.3 - 5.0V |
1219 - 1524 | 3.2 - 4.8V |
1524 - 1829 | 3.0 - 4.6V |
1829 - 2133 | 2.9 - 4.5V |
2133 - 2438 | 2.8 - 4.3V |
2438 - 2743 | 2.6 - 4.2V |
2743 - 3048 | 2.5 - 4.0V |
Engine idling. Does scantool display MAP of 4.0 volts or over?