MAP sensor measures changes in manifold pressure. Changes in manifold pressure result from engine load and speed changes. The MAP sensor converts these changes in manifold pressure into a voltage output signal to control module (1.5 volts at idle to about 4.5 volts at WOT). The control module can monitor these signals and adjust air/fuel ratio and ignition timing under various operating conditions.
If MAP sensor fails, the control module substitutes a fixed MAP value, and uses the TP sensor to control fuel delivery. A fault in the MAP circuit should set a related trouble code. If a related trouble code is not present and MAP sensor is suspected of causing a driveability problem, perform functional check of MAP sensor. See SYSTEM/COMPONENT TESTS - 4.3L article.