Transcript Automotive Wave forms

Automotive Wave forms
Oscilloscope's
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An oscilloscope can be
a priceless price of test
equipment used for
observation of
electrical/electronic
wave patterns.
Oscilloscope's
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To properly use an oscilloscope you must
understand the scale selections.
Must automotive oscilloscope will automatically
adjust to the proper scale.
It’s the technician job to interpret the reading and
determine if the wave form is normal or defective.
Not all devices operate in the same manner
please check manufactures specifications
before replacing any sensor.
Oscilloscope's
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Oscilloscope are used to
measure voltage over a
period of time.
An event that happens over
a period of time is called
frequency and in measured
in Hertz per second.
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1 Second Scale
TIME
Grid lines
15
12.2 filter DC voltage
V
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6 – 9 volts unfiltered DC voltage
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4 Volts Peak to Peak AC Voltage
5
10
1 Second scale
Oscilloscope's
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Filtered voltage: A
smooth supply of
voltage.
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Unfiltered voltage:
Normally a ripple type
wave pattern.
Oscilloscope's
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An AC wave form change
direction from positive to
negative.
Peak voltage: is the
voltage from the highest
positive voltage to the
lowest negative voltage
reading.
+5
0
-5
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Peak to Peak voltage is determine by
multiplying:
Grid division x voltage setting = Peak to peak voltage
Oscilloscope's
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Oscilloscope can be used to measure an
event over a period of time.
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Frequency: Number of complete cycles per
second measured in hertz (Hz).
Hertz (Hz): Unit of measurement for frequency. 1
hertz equal 1 cycle per second.
Oscilloscope's
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To check frequency you may need some
math.
Number of grid lines covered for 1 cycle
divided by the time scale.
Wheel speed sensor
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The Anti-lock Braking
System (ABS) relies
upon information
coming in from speed
sensors.
The wave form
produced is used by
the ABS control module
to determine if wheel
lock-up is occurring.
Two ABS wave forms. Both are good the difference is
the meter set-up
2
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5 mS Time Scale
NORAM ABS PATTERN
2
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2 Volts
10 mS
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10 mS Time Scale
Normal ABS Pattern
Throttle Position Sensor
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A throttle position is
normally produces an
analog signal.
The throttle position is
normally used to tell the
PCM the position of the
throttle
Analog signal: an
electrical signal that varies
in strength.
Throttle Held open
Throttle Snapped
5
4
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2
1
0
200 mS Time Division
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale
5
Defective TPS
4
3
2
1
0
200 mS Time Division
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale
Air Flow Meters
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The voltage output from
the internal track of an
Air Flow Meter (AFM)
should be linear to flap
movement,
This can be measured
on an oscilloscope
MASS AIR FLOW METER
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The waveform should show approximately
1.0 volt when the engine is at idle,
Voltage will rise as engine when engine
speed is increased.
A peak voltage of around 4.5 is normal due to
natural inertia.
Voltage will drop and then level off
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Spike due to
acceleration
Normal float
back to match
air flow
Throttle
Released
Around 1 Volt at idle
Normal falloff caused by
inertia
Hot Wire Air flow Meters
Voltage spike due to
quick throttle opening
Temperature
stabilizes
5
Throttle Released
4
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2
1
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Cold air cooling of wire
At idle around 1 volt normal
250 mS time division
A defective Mass Air Flow will have low voltage or
operate erratic at all throttle angles.
A mass air flow angle should change in relation to
throttle angle.
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1
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250 mS time division
Wave Forms
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Another common type wave form is the
square wave.
Most electronic components are controlled by
a computer PCM, BCM, ECM, ECU or a host
of other names.
When the computer turns on a component it
usually completes a ground circuit sometime
controlling a relay.
Square Wave
Normal voltage spikes
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15
10
5
0
Normal Square wave.
NOTE: Any wave that is on more than
off or off ore than on is called a pulsed
wave.
Pulsed Wave
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Pulsed waves are used to control several
electrical components such as:
Fuel pump
 Canister solenoids
 EGR solenoids
Wave length: The time required for on complete
cycle of a waveform.
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Pulsed Wave
.
The difference in wave length is caused by
circuit demands
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Wave length
0
NORMAL PULSE WAVE
Pulsed Wave
.
20
Voltage did not
drop properly
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Bad pulse wave
Voltage did increase
properly
Coolant Temperature Sensor
(CTS)
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Most coolant sensors are
Negative Temperature
Coefficient (NTC) devices.
The sensor resistance
starts out high around 200
Ohms and drops as engine
temperature increases.
Bad CTS wave form
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V
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S
1
Good CTS waveform
0
50
100
150
200
50 second scale
250
Bad CTS wave forms
Bad CTS sensor or electrical
connection disconnected
waveform
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V
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Bad CTS erratic voltage pattern
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150
200
50 second scale
250
Crankshaft Sensor
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This signal should be test
when the engine fail to start
due to lack ignition.
The crankshaft sensor
produces an AC voltage
that is low while cranking
and increases after the
engine starts.
AC voltage output is critical,
low output can prevent an
engine from starting.
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Even if the signal pattern
look good.
Crankshaft Sensor
Normal due to missing tooth on
reluctor or flywheel.
The missing tooth is used by the PCM
to determine crankshaft position
Crankshaft Sensor
Voltage at start-up
Voltage at higher cranking RPM
NOTE: Operating parameters vary from manufactures
Crankshaft Sensor
Engine Running: Note the higher voltage
Crankshaft Sensor
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A defective crankshaft
sensor will show little or
no output on the
oscilloscope
Proper output voltage is
critical.
1
.8
.6
.4
.2
0
.2
.4
Defective Crankshaft sensor
Voltage to LOW
Knock Sensor
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A knock sensor is used with
some management
systems,
The Knock sensor is a small
piezo-electrical device. That
produces electricity when
vibrated.
Knock sensor are used to
reduce ignition timing when
a spark knock occurs.
Usually no more than 10˚
Knock Sensor
Knock Sensor
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V
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Point where knock occurred
NOTE: Knock sensor output
should normally be zero
0
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50
100
150
50 mS scale
200
250
300
350
Knock Sensor
5
Bad knock sensor pattern
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100
150
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300
Oscilloscope's
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Its important to
remember that all
electrical wiring will
have some type
electrical pattern that
can be view on an
oscilloscope.
Open Circuit
NOTE: Voltage is “0” on an
open circuit
Good ground circuit
Oscilloscope's Quiz
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1. Technician A says pattern A is 
DC voltage. Technician B says
Pattern B is DC voltage. Who is
correct.
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A nor B
Pattern A
Pattern B
Oscilloscope's Quiz
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2. How many seconds
pass from point A to
Pont B?
A. 1
B. 2
C. 3
4. 4
A
1 Second Scale
B
Oscilloscope's Quiz
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3. Technician A says this
pattern is an AC wave form.
Technician B says this is DC
unfiltered. Who is correct?
A. Technician A Only
B. Technician B only
C. Both A and B
D. Neither A nor B
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22
Oscilloscope's Quiz
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4. What is peak Negative
voltage in this pattern?
 A. - 1 volt
 B. - 2 volts
 C. - 4 volts
 D. -.25 volts
2
1
0
1
2
50
100
150
200
Oscilloscope's Quiz
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5. What is peak to peak
voltage in this pattern?
 A. 1 volt
 B. 2 volts
 C. 4 volts
 D. .25 volts
2
1
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1
2
50
100
150
200
Oscilloscope's Quiz
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6. The number of complete cycles per second
measured is:
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A. Amperage
B. Frequency
C. Ohms
D. Voltage
Oscilloscope's Quiz
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7. Technician A says voltage
is measured from point A - B.
Technician B says Time is
measure from point C-D. Who
is correct?
A. Technician A only
B. Technician B only
C. Both A and B
D. Neither A nor B
A
B
C
D
Oscilloscope's Quiz
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8. What time scale is
this oscilloscope set
for?
A. 2 mS
B. 5 mS
C. 10 mS
D. 100 mS
Oscilloscope's Quiz
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9. Technician A says the
wave form is of a defective
TPS (Throttle position
sensor) Technician B says
the pattern is of a good CTS
sensor. Who is correct?
 A. Technician A only
 B. Technician B only
 C. Both A and B
 D. Neither A nor B
5
4
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1
0
50
100 150 200 250
50 Second Scale
Oscilloscope's Quiz
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10. Which diagram is of
a good ground circuit?
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A. 1
B. 2
C. 3
D. 4
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4