Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure Sensor measures the changes in the intake manifold pressure which results from engine load and rpm changes; and converts these changes into a voltage output. The ECM sends a 5 volt reference voltage to the MAP sensor. As the manifold pressure changed, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the manifold pressure. A low pressure (low voltage output) will be around 1-2 volts at idle. While higher pressure (high voltage output) will be around 4-4.8 volts at wide open throttle. The MAP sensor is also used under certain conditions as a barometric pressure sensor. This allows the ECM to make certain adjustments for altitude. The ECM uses the MAP sensor to adjust fuel delivery and ignition timing.

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

IMPORTANT: Be sure to use the same diagnostic equipment for all measurements.

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 Stamp" number. See figures on Chart.

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

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

4. Make sure electrical connector remains securely fastened. Disconnect sensor from bracket and twist sensor by hand only to check for intermittent connection. Output changes greater than 0.1 volt indicate a bad connector or connection. If OK replace sensor.