Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D:

Wiring Diagram:

CIRCUIT DESCRIPTION:

The manifold absolute pressure sensor (MAP) measures manifold pressure (vacuum) and then sends that signal to the ECM. The ECM sends a 5 volt reference voltage to the MAP sensor. As the manifold pressure changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the manifold pressure. A lower pressure output voltage will be about 1 - 2 volts at idle. While higher pressure output voltage will be about 4 - 4.8 volts at Wide Open Throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the ECM to make adjustments for different altitudes. The ECM uses the MAP sensor to control fuel delivery and ignition timing.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. When comparing scan readings to a known good vehicle, it is important to compare vehicles that use a MAP sensor having the same color insert or having the same "hot stamped" number. See figures in chart.

2. Applying 34 kPa (10 inches Hg) vacuum to the MAP sensor should cause the voltage to change. Subtract second reading from the first. Voltage value should be greater than 1.5 volts. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.

3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to the MAP hose.

4. A poor connection at the MAP sensor could cause faulty readings on the "SCAN" tool. If OK, replace sensor.