2. OBJECTIVES After studying Chapter 13, the reader will be able to:
Prepare for ASE Engine Performance (A8) certification test content area “E” (Computerized Engine Controls Diagnosis and Repair).
Discuss how MAP sensors work.
List the methods that can be used to test MAP sensors.
Describe the symptoms of a failed MAP sensor.
List how the operation of the MAP sensor affects vehicle operation.
Discuss MAP sensor rationality tests.

3. AIR PRESSURE—HIGH AND LOW
You can think of an internal combustion engine as a big air pump.
As the pistons move up and down in the cylinders, they pump in air and fuel for combustion and pump out exhaust gases.
They do this by creating a difference in air pressure.
The low pressure within the engine is called vacuum.
Vacuum causes the higher-pressure air on the outside to flow into the low-pressure area inside the cylinder.
The difference in pressure between the two areas is called a pressure differential.

4. AIR PRESSURE—HIGH AND LOW
FIGURE 13-1 (a) As an engine is accelerated under a load, the engine vacuum drops. This drop in vacuum is actually an increase in absolute pressure in the intake manifold. A MAP sensor senses all pressures greater than that of a perfect vacuum. (b) The relationship between absolute pressure, vacuum, and gauge pressure.

5. PRINCIPLES OF PRESSURE SENSORS
To provide the computer with changing air flow information, a fuel-injection system may use a:
Manifold absolute pressure (MAP) sensor
Manifold absolute pressure (MAP) sensor plus barometric absolute pressure (BARO) sensor
Barometric and manifold absolute pressure sensors combined (BMAP).
FIGURE 13-2 A plastic MAP sensor used for training purposes showing the electronic circuit board and electrical connections.

6. CONSTRUCTION OF MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORS
The typical MAP sensor consists of a ceramic or silicon wafer sealed on one side with a perfect vacuum and exposed to intake manifold vacuum on the other side.
As the engine vacuum changes, the pressure difference on the wafer changes the output voltage or frequency of the MAP sensor.
Silicon-Diaphragm Strain Gauge MAP Sensor
Capacitor-Capsule MAP Sensor
Ceramic Disc MAP Sensor

7. CONSTRUCTION OF MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORS
FIGURE 13-3 A DMM set to test a MAP sensor.(1) Connect the red meter lead to the V meter terminal and the black meter lead to the COM meter terminal. (2) Select DC volts. (3) Connect the test leads to the sensor signal wire and the ground wire. (4) Select hertz (Hz) if testing a MAP sensor whose output is a varying frequency; otherwise keep it on DC volts.(5) Read the change of frequency as the vacuum is applied to the sensor. Compare the vacuum reading and the frequency (or voltage) reading to the specifications. (Courtesy of Fluke Corporation)

8. CONSTRUCTION OF MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORS
FIGURE 13-4 A waveform of a typical digital MAP sensor.

9. CONSTRUCTION OF MANIFOLD ABSOLUTE PRESSURE (MAP) SENSORS
FIGURE 13-5 Shown is the electronic circuit inside a ceramic disc MAP sensor used on many Chrysler engines. The black areas are carbon resistors that are applied to the ceramic, and lasers are used to cut lines into these resistors during testing to achieve the proper operating calibration.

10. PCM USES OF THE MAP SENSOR
The PCM uses the MAP sensor to determine the following:
The load on the engine.
Altitude, fuel, and spark control calculations.
EGR system operation.
Detect deceleration (vacuum increases).
Monitor engine condition.
Load detection for returnless-type fuel injection.
Altitude and MAP sensor values.

11. PCM USES OF THE MAP SENSOR
FIGURE 13-6 Altitude affects the MAP sensor voltage.

12. BAROMETRIC PRESSURE SENSOR
A barometric pressure (BARO) sensor is similar in design, but senses more subtle changes in barometric absolute pressure (atmospheric air pressure).
It is vented directly to the atmosphere.
The barometric manifold absolute pressure (BMAP) sensor is actually a combination of a BARO and MAP sensor in the same housing.

13. TESTING THE MAP SENSOR
Most pressure sensors operate on 5 volts from the computer and return a signal (voltage or frequency) based on the pressure (vacuum) applied to the sensor.
If a MAP sensor is being tested, make certain that the vacuum hose and hose fittings are sound and making a good, tight connection to a manifold vacuum source on the engine.
Testing the MAP Sensor Using a DMM or Scope
Testing the MAP Sensor Using a Scan Tool

14. TESTING THE MAP SENSOR
FIGURE 13-7 A typical hand-operated vacuum pump.

15. FUEL-RAIL PRESSURE SENSOR
A fuel-rail pressure (FRP) sensor is used on some vehicles such as Fords that are equipped with electronic returnless fuel injection.
This sensor provides fuel pressure information to the PCM for fuel injection pulse width calculations.

16. MAP/BARO DIAGNOSTIC TROUBLE CODES
The diagnostic trouble codes (DTCs) associated with the MAP and BARO sensors include:

17. Three types of MAP sensors include:
SUMMARY
Pressure below atmospheric pressure is called vacuum and is measured in inches of mercury.
A manifold absolute pressure sensor uses a perfect vacuum (zero absolute pressure) in the sensor to determine the pressure.
Three types of MAP sensors include:
Silicon-diaphragm strain gauge
Capacitor-capsule design
Ceramic disc design

18. SUMMARY
A heavy engine load results in low intake manifold vacuum and a high MAP sensor signal voltage.
A light engine load results in high intake manifold vacuum and a low MAP sensor signal voltage.
A MAP sensor is used to detect changes in altitude, as well as check other sensors and engine systems.
A MAP sensor can be tested by visual inspection, testing the output using a digital meter or scan tool.

19. REVIEW QUESTIONS
What is the relationship among atmospheric pressure, vacuum, and boost pressure in PSI?
What are two types (construction) of MAP sensors?
What is the MAP sensor signal voltage or frequency at idle on a typical General Motors, Chrysler, and Ford engine?
What are three uses of a MAP sensor by the PCM?

20. CHAPTER QUIZ
As the load on an engine increases, the manifold vacuum decreases and the manifold absolute pressure _____.
Increases
Decreases
Changes with barometric pressure only (altitude or weather)
Remains constant (absolute)

21. CHAPTER QUIZ
As the load on an engine increases, the manifold vacuum decreases and the manifold absolute pressure _____.
Increases
Decreases
Changes with barometric pressure only (altitude or weather)
Remains constant (absolute)

22. CHAPTER QUIZ
2. A typical MAP compares the vacuum in the intake manifold to _____.
Atmospheric pressure
A perfect vacuum
Barometric pressure
The value of the IAT sensor

23. CHAPTER QUIZ
2. A typical MAP compares the vacuum in the intake manifold to _____.
Atmospheric pressure
A perfect vacuum
Barometric pressure
The value of the IAT sensor

24. CHAPTER QUIZ 3. Which statement is false?
Absolute pressure is equal to barometric pressure plus intake manifold vacuum.
A decrease in manifold vacuum means an increase in manifold pressure.
The MAP sensor compares manifold vacuum to a perfect vacuum.
Barometric pressure minus the MAP sensor reading equals intake manifold vacuum.

25. CHAPTER QUIZ 3. Which statement is false?
Absolute pressure is equal to barometric pressure plus intake manifold vacuum.
A decrease in manifold vacuum means an increase in manifold pressure.
The MAP sensor compares manifold vacuum to a perfect vacuum.
Barometric pressure minus the MAP sensor reading equals intake manifold vacuum.

26. CHAPTER QUIZ
4. Which design of MAP sensor produces a frequency (digital) output signal?
Silicon-diaphragm strain gauge
Piezoresistivity design
Capacitor-capsule
Ceramic disc

27. CHAPTER QUIZ
4. Which design of MAP sensor produces a frequency (digital) output signal?
Silicon-diaphragm strain gauge
Piezoresistivity design
Capacitor-capsule
Ceramic disc

28. CHAPTER QUIZ
5. The frequency output of a digital MAP sensor is reading 114 Hz. What is the approximate engine vacuum?
Zero
5 in. Hg
10 in. Hg
15 in. Hg

29. CHAPTER QUIZ
5. The frequency output of a digital MAP sensor is reading 114 Hz. What is the approximate engine vacuum?
Zero
5 in. Hg
10 in. Hg
15 in. Hg

30. CHAPTER QUIZ 6. Which is not a purpose or function of the MAP sensor?
Measures the load on the engine
Measures engine speed
Calculates fuel delivery based on altitude
Helps diagnose the EGR system

31. CHAPTER QUIZ 6. Which is not a purpose or function of the MAP sensor?
Measures the load on the engine
Measures engine speed
Calculates fuel delivery based on altitude
Helps diagnose the EGR system

32. CHAPTER QUIZ
7. When measuring the output signal of a MAP sensor on a General Motors vehicle, the digital multimeter should be set to read _____.
DC V
AC V Hz
DC A

33. CHAPTER QUIZ
7. When measuring the output signal of a MAP sensor on a General Motors vehicle, the digital multimeter should be set to read _____.
DC V
AC V Hz
DC A

34. CHAPTER QUIZ
8. Two technicians are discussing testing MAP sensors. Technician A says that the MAP sensor should be replaced if anything comes out of the sensor when the vacuum hose is removed from the sensor. Technician B says that the injector pulse width should increase when vacuum to the MAP sensor is increased. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

35. CHAPTER QUIZ
8. Two technicians are discussing testing MAP sensors. Technician A says that the MAP sensor should be replaced if anything comes out of the sensor when the vacuum hose is removed from the sensor. Technician B says that the injector pulse width should increase when vacuum to the MAP sensor is increased. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

36. CHAPTER QUIZ
9. Technician A says that MAP sensors use a 5-volt reference voltage from the PCM. Technician B says that the MAP sensor voltage will be higher at idle at high altitudes compared to when the engine is operating at near sea level. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

37. CHAPTER QUIZ
9. Technician A says that MAP sensors use a 5-volt reference voltage from the PCM. Technician B says that the MAP sensor voltage will be higher at idle at high altitudes compared to when the engine is operating at near sea level. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

38. CHAPTER QUIZ
10. A P0107 DTC is being discussed. Technician A says that a defective MAP sensor could be the cause. Technician B says that a MAP sensor signal wire shorted-to-ground could be the cause. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

39. CHAPTER QUIZ
10. A P0107 DTC is being discussed. Technician A says that a defective MAP sensor could be the cause. Technician B says that a MAP sensor signal wire shorted-to-ground could be the cause. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B