OBJECTIVES
After studying Chapter 12, 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 throttle position sensors work.
3. List the methods that can be used to test TP
sensors.
4. Describe the symptoms of a failed TP sensor.
5. List how the operation of the TP sensor affects
vehicle operation.
6. Discuss TP 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
THROTTLE POSITION SENSORS
• Most computer-equipped engines use a throttle position
(TP) sensor to signal to the computer the position of the
throttle.
FIGURE 12-1 A typical TP sensor mounted on the throttle plate of this
port-injected engine.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSORS
• Potentiometers
– A potentiometer is a variableresistance sensor with three
terminals.
FIGURE 12-2 The signal voltage from a throttle position increases
as the throttle is opened because the wiper arm is closer to the 5volt reference. At idle, the resistance of the sensor winding
effectively reduces the signal voltage output to the computer.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TP SENSOR COMPUTER INPUT FUNCTIONS
• The computer senses any change in throttle
position and changes the fuel mixture and ignition
timing.
• The throttle position (TP) sensor used on fuelinjected vehicles acts as an “electronic accelerator
pump.”
• The PCM supplies the TP sensor with a regulated
voltage that ranges from 4.8 to 5.1 volts.
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 THE TP SENSOR
• The TP sensor is used by the powertrain control
module (PCM) for the following reasons.
–
–
–
–
–
–
–
Clear Flood Mode
Torque Converter Clutch Engagement and Release
Rationality Testing for MAP and MAF Sensors
Automatic Transmission Shift Points
Target Idle Speed (Idle Control Strategy)
Air-Conditioning Compressor Operation
Backs Up Other Sensors
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING THE THROTTLE POSITION SENSOR
• A TP sensor can be tested using one or more of the
following tools:
– A digital voltmeter with three test leads connected in
series between the sensor and the wiring harness
connector or back probing using T-pins.
– A scan tool or a specific tool recommended by the vehicle
manufacturer.
– A breakout box that is connected in series between the
computer and the wiring harness connector(s).
– An oscilloscope.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING THE THROTTLE POSITION SENSOR
FIGURE 12-3 A meter lead connected to a T-pin that was gently pushed along
the signal wire of the TP sensor until the point of the pin touched the metal
terminal inside the plastic connector.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING THE THROTTLE POSITION SENSOR
• The procedure for testing the sensor using a digital
multimeter is as follows:
– Turn the ignition switch on (engine off).
– Measure the voltage between the signal wire and ground
(reference low) wire. The voltage should be about 0.5
volt.
– With the engine still not running (but with the ignition still
on), slowly increase the throttle opening. The voltage
signal from the TP sensor should also increase.
– With the voltmeter still connected, slowly return the
throttle down to the idle position. The voltage from the TP
sensor should also decrease evenly on the return to idle.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING THE THROTTLE POSITION SENSOR
FIGURE 12-4 A typical
waveform of a TP sensor
signal as recorded on a DSO
when the accelerator pedal
was depressed with the
ignition switch on (engine
off). Clean transitions and the
lack of any glitches in this
waveform indicate a good
sensor. (Courtesy of Fluke
Corporation)
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHECK POWER AND GROUND BEFORE
CONDEMNING A BAD SENSOR
FIGURE 12-5 Checking the
5-volt reference from the
computer being applied to
the TP sensor with the
ignition switch on (engine
off).
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHECK POWER AND GROUND BEFORE
CONDEMNING A BAD SENSOR
FIGURE 12-6 Checking the voltage drop between the TP sensor ground and a
good engine ground with the ignition on (engine off). A reading of greater than
0.2 volt (200 mV) represents a bad computer ground.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TESTING A TP SENSOR USING THE MIN/MAX
FUNCTION
• Many digital multimeters are capable of recording
voltage readings over time and then displaying the
minimum, maximum, and average readings. To
perform a MIN/MAX test of the TP sensor, manually
set the meter to read higher than 4 volts.
– Connect the red meter lead to the signal wire and the
black meter lead to a good ground on the ground return
wire at the TP sensor.
– With the ignition on, engine off, slowly depress and
release the accelerator pedal from inside the vehicle.
– Check the minimum and maximum voltage reading on the
meter display. Any 0- or 5-volt reading would indicate a
fault or short in the TP sensor.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
TP SENSOR DIAGNOSTIC TROUBLE CODES
• The diagnostic trouble
codes (DTCs) associated
with the throttle position
sensor include the
following.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
THROTTLE POSITION SENSOR DIAGNOSIS
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 throttle position (TP) sensor is a three-wire variable
resistor called a potentiometer.
2. The three wires on the TP sensor include a 5-volt reference
voltage from the PCM, plus the signal wire to the PCM, and
a ground, which also goes to the PCM.
3. The TP sensor is used by the PCM for clear flood mode,
torque converter engagement and release, and automotive
transmission shift points, as well as for rationality testing for
the MAP and MAF sensor.
4. The TP sensor signal voltage should be about 0.5 volt at
idle and increase to about 4.5 volts at wide-open throttle
(WOT).
5. A TP sensor can be tested using a digital multimeter, a
digital storage oscilloscope (DSO), or a scan tool.
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. What is the purpose of each of the three
wires on a typical TP sensor?
2. What all does the PCM do with the TP
sensor signal voltage?
3. What is the procedure to follow when
checking the 5-volt reference and TP sensor
ground?
4. How can a TP sensor be diagnosed using a
scan tool?
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. Which sensor is generally considered to be the
electronic accelerator pump of a fuel-injected
engine?
a)
b)
c)
d)
O2S
ECT sensor
Engine MAP sensor
TP 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
1. Which sensor is generally considered to be the
electronic accelerator pump of a fuel-injected
engine?
a)
b)
c)
d)
O2S
ECT sensor
Engine MAP sensor
TP 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
2. Typical TP sensor voltage at idle is about ______.
a)
b)
c)
d)
2.50 to 2.80 volts
0.5 volt or 10% of WOT TP sensor voltage
1.5 to 2.8 volts
13.5 to 15.0 volts
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. Typical TP sensor voltage at idle is about ______.
a)
b)
c)
d)
2.50 to 2.80 volts
0.5 volt or 10% of WOT TP sensor voltage
1.5 to 2.8 volts
13.5 to 15.0 volts
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. A TP sensor is what type of sensor?
a)
b)
c)
d)
Rheostat
Voltage generating
Potentiometer
Piezoelectric
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. A TP sensor is what type of sensor?
a)
b)
c)
d)
Rheostat
Voltage generating
Potentiometer
Piezoelectric
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. Most TP sensors have how many wires?
a)
b)
c)
d)
1
2
3
4
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. Most TP sensors have how many wires?
a)
b)
c)
d)
1
2
3
4
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. Which sensor does the TP sensor backup if the
PCM determines that a failure has occurred?
a)
b)
c)
d)
Oxygen sensor
MAF sensor
MAP sensor
Either b or c
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. Which sensor does the TP sensor backup if the
PCM determines that a failure has occurred?
a)
b)
c)
d)
Oxygen sensor
MAF sensor
MAP sensor
Either b or c
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. Which wire on a TP sensor should be back-probed
to check the voltage signal to the PCM?
a)
b)
c)
d)
5-volt reference (Vref)
Signal
Ground
Meter should be connected between the 5-volt reference
and the ground
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. Which wire on a TP sensor should be back-probed
to check the voltage signal to the PCM?
a)
b)
c)
d)
5-volt reference (Vref)
Signal
Ground
Meter should be connected between the 5-volt reference
and the ground
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. After a TP sensor has been tested using the
MIN/MAX function on a DMM, a reading of zero
volts is displayed. What does this reading
indicate?
a)
b)
c)
d)
The TP sensor is open at one point during the test.
The TP sensor is shorted.
The TP sensor signal is shorted to 5-volt reference.
Both b and c are possible.
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. After a TP sensor has been tested using the
MIN/MAX function on a DMM, a reading of zero
volts is displayed. What does this reading
indicate?
a)
b)
c)
d)
The TP sensor is open at one point during the test.
The TP sensor is shorted.
The TP sensor signal is shorted to 5-volt reference.
Both b and c are possible.
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. After a TP sensor has been tested using the
MIN/MAX function on a DMM, a reading of 5 volts
is displayed. What does this reading indicate?
a)
b)
c)
d)
The TP sensor is open at one point during the test.
The TP sensor is shorted.
The TP sensor signal is shorted to 5-volt reference.
Both b and c are possible.
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. After a TP sensor has been tested using the
MIN/MAX function on a DMM, a reading of 5 volts
is displayed. What does this reading indicate?
a)
b)
c)
d)
The TP sensor is open at one point during the test.
The TP sensor is shorted.
The TP sensor signal is shorted to 5-volt reference.
Both b and c are possible.
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. A technician attaches one lead of a digital voltmeter to the
ground terminal of the TP sensor and the other meter lead
to the negative terminal of the battery. The ignition is
switched to on, engine off and the meter displays 37.3 mV.
Technician A says that this is the signal voltage and is a
little low. Technician B says that the TP sensor ground
circuit has excessive resistance. 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
9. A technician attaches one lead of a digital voltmeter to the
ground terminal of the TP sensor and the other meter lead
to the negative terminal of the battery. The ignition is
switched to on, engine off and the meter displays 37.3 mV.
Technician A says that this is the signal voltage and is a
little low. Technician B says that the TP sensor ground
circuit has excessive resistance. 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 P0122 DTC is retrieved using a scan tool. This
DTC means ______ .
a)
b)
c)
d)
The TP sensor voltage is low
The TP sensor could be shorted-to-ground
The TP sensor signal circuit could be shorted-to-ground
All of the above are correct.
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 P0122 DTC is retrieved using a scan tool. This
DTC means ______ .
a)
b)
c)
d)
The TP sensor voltage is low
The TP sensor could be shorted-to-ground
The TP sensor signal circuit could be shorted-to-ground
All of the above are correct.
Advanced Engine Performance Diagnosis, 4/e
By James D. Halderman
© 2009 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458