Manifold Pressure/Vacuum Sensor: Testing and Inspection
MANIFOLD ABSOLUTE PRESSURE (MAP) OUTPUT CHECK
Circuit Description
The manifold absolute pressure (MAP) sensor measures the changes in the intake MAP which result from Engine load (intake manifold vacuum) and Engine speed changes; and converts these into a voltage output. The Powertrain Control Module (PCM) sends a 5-volt reference voltage to the MAP sensor. As the MAP changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the MAP. A lower pressure (low voltage) output voltage will be about 1 - 2 volts at idle. Higher pressure (high voltage) output voltage will be about 4.0 - 4.8 volts at wide open throttle. 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 diagnose proper operation of the Exhaust Gas Recirculation (EGR) system, in addition to other functions.
Test Description
Number(s) below refer to the step number(s) in the Diagnostic Test:
NOTE: Be sure to use the same diagnostic test equipment for all measurements.
1. When you compare the Scan Tool readings to a known good vehicle, it is important to compare vehicles that use MAP sensors that have the same color insert (2) or the same "Hot Stamped" (1) number. (Numbers refer to the image.)
2. Applying 34 kPa (10 Hg) vacuum to the MAP sensor should cause the voltage to be 1.5 - 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 the vacuum hose to the sensor for leaking or restriction. Be sure that no other vacuum devices are connected to the MAP hose.
NOTE: Make sure the electrical connector remains securely fastened.
4. Disconnect the sensor from the bracket. Twist the sensor with your hand to check for an intermittent connection. Output changes greater than 0.10 volt indicate a bad sensor.
Diagnostic Test
1. a. Turn the ignition "OFF" and leave it "OFF" for 15 seconds.
b. Ignition "ON". Don't crank Engine.
c. The Scan Tool should indicate a manifold absolute pressure (MAP) sensor voltage.
d. Compare this scan reading to the scan reading of a known good vehicle obtained using the exact same procedure as in Steps 1-4.
e. Is the voltage reading the same ± 0.40 volt?
[YES] Go to Step 2.
[NO] Go to Step 5.
2. a. Disconnect the vacuum hose at the MAP sensor and plug the hose.
b. Connect a hand vacuum pump to the MAP sensor.
c. Start the Engine.
d. Apply 34 kPa (10 Hg) of vacuum and note the voltage change.
e. Is the voltage change 1.5-2.1 volts less than step 1?
[YES] Go to Step 3.
[NO] Go to Step 4.
3. a. No trouble found. Check the sensor hose for leakage or restriction.
b. Does the hose supply vacuum to the MAP sensor only?
[YES] Go to Step 5.
[NO] Go to Step 4.
4. a. Repair the hose to ensure the hose supplies vacuum to the MAP sensor only.
b. Is the action complete?
[YES] Verify repair.
5. a. Check the sensor connection.
b. Is the sensor connection good?
[YES] Go to Step 6.
[NO] Go to Step 7.
6. a. Replace the sensor.
b. Is the action complete?
[YES] Verify repair.
7. a. Repair the poor connection.
b. Is the action complete?
[YES] Verify repair.