MAP Sensor Output Diagnosis

MAP Circuit:

SYSTEM 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 changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the manifold pressure. At lower pressure output voltage will be about 1 to 2 volts at idle. While at higher pressure or at Wide Open Throttle (WOT) output voltage will be about 4 to 4.8 volts. 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.

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

CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
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 and the same "Hot Stamped" number. Refer to Figures 1 and 2 inside diagnostic chart.
2. Applying 34 kPa (10" Hg) vacuum to the MAP sensor should result in voltage readings of 1.5 to 2.1 volts less than the voltage in 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 seal to sensor for leaking or restriction.

NOTICE: Make sure electrical connector remains securely fastened.

4. Disconnect sensor from the intake plenum and twist sensor (by hand only) to check for intermittent connection. Output changes greater than 0.10 volt indicate a faulty sensor or connection. If OK, replace sensor.