J2000/Sunbird V6-191 3.1L VIN T MFI (1994)
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 PCM 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 PCM knows the manifold pressure. A
lower pressure (low voltage) output voltage will be about 1-2 volts at idle, while 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 used the MAP sensor to control fuel delivery and ignition timing
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 scan tool 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 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 that no other vacuum devices are connected to the MAP hose.
Note: Make sure electrical connector remains securely fastened.
Diagnostic Aids:
Remove the MAP sensor from its bracket and gently twist sensor (by hand only) while observing the MAP display on a scan tool. Make sure
electrical connector remains securely fastened. This is a good way to check for intermittent failures. Output fluctuations greater than .1 volt indicate a
faulty sensor.
