Manifold Pressure/Vacuum Sensor: Testing and Inspection

Manifold Absolute Pressure (MAP) Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor measures the ablolute pressure inside the intake manifold, which changes depending on throttle position, engine speed and engine load. The PCM applies a 5 volt reference voltage to a terminal of the MAP sensor. Depending on the absolute pressure in the intake manifold, the MAP sensor divides the current from the reference source between a signal circuit and ground at different ratios, which varies the voltage in the signal circuit. Each specific signal voltage corresponds to a specific absolute pressure. The lower the manifold pressure (high vacuum), the lower the voltage output from the MAP sensor. The sensors output ranges from about 1-2 volts at idle, to about 4-4.8 volts at wide open throttle. The PCM monitors the MAP sensor signal voltage and calculates the pressure in the intake manifold.

TEST DESCRIPTION

Chert C-1D, MAP Sensor Output Check:

Numbers below refer to circled numbers in the diagnostic chart.

NOTE: Be sure to use the same test equipment for all measurements. Differences in impedence between different voltmeters may affect test results of low voltage/low current circuits such as these.

1. When comparing "SCAN" tool readings to a known good vehicle, be sure MAP sensors in both vehicles have the same "Hot Stamped" identification number.
2. With 34 kPa (10" Hg) vacuum applied to the MAP sensor, voltage reading should drop to 1.5 - 2.1 volts below voltage measured in step 1. Voltage change should be instantaneous as vacuum is applied. If voltage reading is slow to change, check for restriction inside vacuum nipple of sensor. If there is no restriction, MAP sensor is faulty.
3. Check vacuum hose to sensor for leaks or restriction. Be sure vacuum is connected to correct source and no other vacuum devices are connected to the same line.
4. Remove sensor from bracket. Leave electrical connector attached, and wiggle sensor connector while monitoring output voltage. Changes in the output voltage of greater than 0.1 volt indicate a poor connection.