Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D Manifold Absolute Pressure (MAP) Output Check:

Manifold Absolute Pressure (MAP) Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load (intake manifold vacuum) and RPM changes. and converts these into a voltage output. The Powertrain Control Module (PCM) 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 PCM knows the manifold pressure. A lower pressure (low voltage) output voltage will be about 1 - 2 volts at idle. While a higher pressure (high voltage) output voltage will be about 4 - 4.8 at Wide Open Throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the PCM to make adjustments for different altitudes. The PCM uses the MAP sensor to control fuel delivery and ignition timing.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

Note: Be sure to use the same Diagnostic Test Equipment for all measurements.

1. When comparing Tech 1 Scanner reading 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. Refer to image.
If MAP sensor voltage is greater than 5 volts, check for a short to voltage on the MAP sensor signal circuit.
2. Applying 34 kPa (10" Hg) vacuum to the MAP sensor should cause the voltage to change. Voltage change 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 for vacuum leaks or restrictions at intake mounting surface.

Note: Make sure electrical connector remains securely fastened.