OK, I already know it has to do with low voltage of the MAP sensor but what does that mean exactly? It came up this morning as I was hitting the gas to take off from a stop sign. The blazer kind of bucked back and forth then took off and the SES light came on. Any help? Thanks.

 

The Manifold Absolute Pressure (MAP) sensor responds to changes in the intake manifold pressure (vacuum). A 5 volt reference is applied to the sensor on the 5 volt reference circuit. A variable resistor moves in relation to the manifold pressure and a voltage signal is sent back to the VCM on the MAP signal circuit. This voltage signal varies from 1.0-1.5volts at closed throttle to 4.0-4.5volts at wide open throttle (low vacuum). The VCM utilizes the MAP signal and throttle position in order to determine the correct amount of fuel delivered to the engine.
With the ignition ON and the engine OFF, the manifold pressure is equal to the atmospheric pressure (signal voltage high). The VCM uses this information as an indication of the altitude of the vehicle.
Comparison of this reading with a known good vehicle using the same sensor is a good way to check the accuracy of a suspect sensor. The readings should be the same ±0.4volts
Check for vacuum leaks before you replace the sensor.