Manifold Pressure/Vacuum Sensor: Testing and Inspection

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

Wiring Diagram For Chart C-1D - Manifold Absolute Pressure (MAP) Voltage Ouput Check:

CHART C-1D - MANIFOLD ABSOLUTE PRESSURE 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 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 lower pressure (low voltage) output voltage will be about 1 to 2 volts at idle. While higher pressure (high voltage) output voltage will be about 4 to 4.8 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.

Important!

^ Be sure to use the same Diagnostic Test 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 Stamped" number.

2. Applying 34 kPa (10" Hg) vacuum to the MAP sensor should cause the voltage to be 1.5 to 2.1 volts less than the voltage at Step 1. 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 that no other vacuum devices are connected to the MAP hose.


NOTE: Make sure electrical connector remains securely fastened.


4. Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connection. Output changes greater than .10 volt indicate a bad sensor.