Manifold Pressure/Vacuum Sensor: Description and Operation

Manifold Absolute Pressure (MAP) Sensor:

NOTE:
This vehicle may be equipped with either Sequential Fuel Injection (SFI) or Multiport Fuel Injection (MFI). SFI vehicles use a Mass Air Flow (MAF) sensor while MFI vehicles are equipped with a Manifold Absolute Pressure (MAP) sensor

PURPOSE
The Manifold Absolute Pressure (MAP) sensor produces an output signal proportional to engine load. The MAP sensor measures manifold vacuum and converts this to a frequency signal. Low engine vacuum corresponds to high engine load and high vacuum corresponds to a light engine load. The PCM uses the engine load data to establish the optimum fuel injection base pulse width, ignition timing advance, and EGR flow

The MAP sensor also acts as a Barometric Pressure (BP) sensor when the key is on and the engine is not running and at Wide Open Throttle (WOT). This allow the PCM to compensate for changes in altitude and atmospheric pressure.

CONSTRUCTION
The MAP sensor utilizes a pressure sensitive piezoelectric disc. The electrical characterics of the disc change with the amount of pressure applied to it.

OPERATION
A vacuum line connects the MAP sensor sensing port to the intake manifold. The manifold vacuum is converted to an electrical signal by the piezoelectric disc. This signal is then converted by circuitry within the MAP sensor to a frequency modulated output signal.

The output frequency of the MAP sensor varies directly with engine load and indirectly with manifold vacuum. The normal operating range of the MAP sensor is 159Hz (0.0 in Hg) to 95Hz (24.0 in Hg).

The MAP sensor uses a three wire connection.

- VREF is a 5.0 volt reference signal from the PCM, used as a power supply by the MAP sensor.

- MAP/BARO SIG is the MAP sensor output.

- SIG RTN is the sensor ground.

RELATED DIAGNOSTIC TROUBLE CODES

DTC 22/126 - BP/MAP sensor output out of range during self-test (140hz-160hz).

DTC 81/128 - MAP sensor vacuum did not change by more than 2 inches during normal engine operation.

DTC 72/129 - MAP sensor output did not change enough during the dynamic response (snap throttle) test.