OBJECTIVES
After studying Chapter 14, the reader will be able to:
1. Prepare for ASE Engine Performance (A8)
certification test content area “E” (Computerized
Engine Controls Diagnosis and Repair).
2. Discuss how MAF sensors work.
3. List the methods that can be used to test MAF
sensors.
4. Describe the symptoms of a failed MAF sensor.
5. List how the operation of the MAF sensor affects
vehicle operation.
6. Discuss MAF sensor rationality tests.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
AIR FLOW SENSORS
• Port electronic fuel-injection
systems that use air flow
volume for fuel calculation
usually have a movable
vane in the intake stream.
• The vane is part of the
vane air flow (VAF)
sensor.
• The vane is deflected by
intake air flow.
FIGURE 14-1 A vane air flow (VAF) sensor.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
AIR FLOW SENSORS
FIGURE 14-2 A typical air vane sensor with the cover removed. The movable arm contacts a
carbon resistance path as the vane opens. Many air vane sensors also have contacts that
close to supply voltage to the electric fuel pump as the air vane starts to open when the engine
is being cranked and air is being drawn into the engine.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MASS AIR FLOW SENSOR TYPES
• Hot Film Sensor
– The hot film sensor uses a temperature-sensing resistor
(thermistor) to measure the temperature of the incoming
air.
• Hot Wire Sensor
– The hot wire sensor is similar to the hot film type, but
uses a hot wire to sense the mass air flow instead of the
hot film.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MASS AIR FLOW SENSOR TYPES
FIGURE 14-3 This five-wire mass air flow sensor consists of a metal foil sensing
unit, an intake air temperature (IAT) sensor, and the electronic module.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MASS AIR FLOW SENSOR TYPES
FIGURE 14-4 The sensing wire in a typical hot wire mass air flow sensor.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KARMAN VORTEX SENSORS
• In 1912, a Hungarian scientist named Theodore Van
Karman observed that vortexes were created when
air passed over a pointed surface.
• There are two basic designs of Karman Vortex air
flow sensors. The two types include:
– Ultrasonic.
– Pressure-type.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KARMAN VORTEX SENSORS
FIGURE 14-5 A Karman Vortex air flow sensor uses a triangle-shaped rod to
create vortexes as the air flows through the sensor. The electronics in the sensor
itself converts these vortexes to a digital square wave signal.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PCM USES FOR AIR FLOW SENSORS
• The PCM uses the information from the air flow
sensor for the following purposes:
– Air flow sensors are used mostly to determine the amount
of fuel needed and base pulse-width numbers.
• The greater the mass of the incoming air, the longer the injectors are
pulsed on.
– Air flow sensors back up the TP sensor in the event of a
loss of signal or an inaccurate throttle position sensor
signal.
• If the MAF sensor fails, then the PCM will calculate the fuel delivery
needs of the engine based on throttle position and engine speed (RPM).
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING MASS AIR FLOW SENSORS
• Start the testing of a MAF sensor by performing a
thorough visual inspection.
• Look at all the hoses that direct and send air,
especially between the MAF sensor and the throttle
body.
• Also check the electrical connector for:
– Corrosion
– Terminals that are bent or pushed out of the plastic
connector
– Frayed wiring
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING MASS AIR FLOW SENSORS
• MAF Sensor Output Test
• Tap Test
• Digital Meter Test of a MAF Sensor
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
WHAT IS FALSE AIR?
FIGURE 14-6 Carefully check the hose between the MAF sensor and the throttle
plate for cracks or splits that could create extra (false) air into the engine that is
not measured by the MAF sensor.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MAF SENSOR CONTAMINATION
• Dirt, oil, silicon, or even spider webs can coat the sensing
wire.
– Because it tends to insulate the sensing wire at low air flow rates, a
contaminated sensor often overestimates the amount of air entering
the engine at idle, and therefore causes the fuel system to go rich.
• At higher engine speeds near wideopen throttle (WOT), the
contamination can cause the sensor to underestimate the
amount of air entering the engine.
– As a result, the fuel system will go lean, causing spark knock and lack
of power concerns.
• To check for contamination, check the fuel trim numbers.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THE RICH RUNNING TOYOTA
FIGURE 14-7 (a) Air flow sensor with the protective cover removed.(b)
Broken air flow vane return spring.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
MAF-RELATED DIAGNOSTIC TROUBLE CODES
• The diagnostic trouble codes (DTCs) associated with the
mass air flow and air vane sensors include:
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
1. A mass air flow sensor actually measures the
density and amount of air flowing into the engine,
which results in accurate engine control.
2. An air vane sensor measures the volume of the air,
and the intake air temperature sensor is used by
the PCM to calculate the mass of the air entering
the engine.
3. A hot wire MAF sensor uses the electronics in the
sensor itself to heat a wire 70°C above the
temperature of the air entering the engine.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
REVIEW QUESTIONS
1. How does a hot film MAF sensor work?
2. What type of voltage signal is produced by a MAF?
3. What change in the signal will occur if engine
speed is increased?
4. How is a MAF sensor tested?
5. What is the purpose of a MAF sensor?
6. What are the types of air flow sensors?
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. A fuel-injection system that does not use a sensor
to measure the amount (or mass) of air entering
the engine is usually called a(n) _____ type of
system.
a)
b)
c)
d)
Air vane-controlled
Speed density
Mass air flow
Hot wire
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. A fuel-injection system that does not use a sensor
to measure the amount (or mass) of air entering
the engine is usually called a(n) _____ type of
system.
a)
b)
c)
d)
Air vane-controlled
Speed density
Mass air flow
Hot wire
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. Which type of sensor uses a burn-off circuit?
a)
b)
c)
d)
Hot wire MAF sensor
Hot film MAF sensor
Vane-type air flow sensor
Both a and b
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. Which type of sensor uses a burn-off circuit?
a)
b)
c)
d)
Hot wire MAF sensor
Hot film MAF sensor
Vane-type air flow sensor
Both a and b
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. Which sensor has a switch that controls the
electric fuel pump?
a)
b)
c)
d)
VAF
Hot wire MAF
Hot filter MAF
Karman Vortex sensor
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. Which sensor has a switch that controls the
electric fuel pump?
a)
b)
c)
d)
VAF
Hot wire MAF
Hot filter MAF
Karman Vortex sensor
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. Two technicians are discussing Karman Vortex
sensors. Technician A says that they contain a
burn-off circuit to keep them clean. Technician B
says that they contain a movable vane. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. Two technicians are discussing Karman Vortex
sensors. Technician A says that they contain a
burn-off circuit to keep them clean. Technician B
says that they contain a movable vane. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. The typical MAF reading on a scan tool with the
engine at idle speed and normal operating
temperature is _____.
a)
b)
c)
d)
1 to 3 grams per second
3 to 7 grams per second
8 to 12 grams per second
14 to 24 grams per second
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. The typical MAF reading on a scan tool with the
engine at idle speed and normal operating
temperature is _____.
a)
b)
c)
d)
1 to 3 grams per second
3 to 7 grams per second
8 to 12 grams per second
14 to 24 grams per second
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Two technicians are diagnosing a poorly running
engine. There are no diagnostic trouble codes.
When the MAF sensor is unplugged, the engine
runs better. Technician A says that this means that
the MAF is supplying incorrect air flow information
to the PCM. Technician B says that this indicates
that the PCM is defective. Which technician is
correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. Two technicians are diagnosing a poorly running
engine. There are no diagnostic trouble codes.
When the MAF sensor is unplugged, the engine
runs better. Technician A says that this means that
the MAF is supplying incorrect air flow information
to the PCM. Technician B says that this indicates
that the PCM is defective. Which technician is
correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. A MAF sensor on a General Motors 3800 V-6 is being
tested for contamination. Technician A says that the sensor
should show over 100 grams per second on a scan tool
display when the accelerator is depressed to WOT on a
running engine. Technician B says that the output
frequency should exceed 7,000 Hz when the accelerator
pedal is depressed to WOT on a running engine. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. A MAF sensor on a General Motors 3800 V-6 is being
tested for contamination. Technician A says that the sensor
should show over 100 grams per second on a scan tool
display when the accelerator is depressed to WOT on a
running engine. Technician B says that the output
frequency should exceed 7,000 Hz when the accelerator
pedal is depressed to WOT on a running engine. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. Which air flow sensor has a dampening chamber?
a)
b)
c)
d)
A vane airflow
A hot film MAF
A hot wire MAF
A Karman Vortex
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8. Which air flow sensor has a dampening chamber?
a)
b)
c)
d)
A vane airflow
A hot film MAF
A hot wire MAF
A Karman Vortex
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. Air that enters the engine without passing through
the air flow sensor is called _____.
a)
b)
c)
d)
Bypass air
Dirty air
False air
Measured air
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. Air that enters the engine without passing through
the air flow sensor is called _____.
a)
b)
c)
d)
Bypass air
Dirty air
False air
Measured air
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. A P0102 DTC is being discussed. Technician A
says that a sensor circuit shorted-to-ground can be
the cause. Technician B says that an open sensor
voltage supply circuit could be the cause. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. A P0102 DTC is being discussed. Technician A
says that a sensor circuit shorted-to-ground can be
the cause. Technician B says that an open sensor
voltage supply circuit could be the cause. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458