1. Automotive Wave forms

2. Oscilloscope's
An oscilloscope can be a priceless price of test equipment used for observation of electrical/electronic wave patterns.

3. Oscilloscope's
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.

4. Oscilloscope's
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. 20 15 10 5
VOLTAGE
1 Second Scale
TIME

5. Grid lines 15 10 12.2 filter DC voltage V 5 O L T A G
12.2 filter DC voltage V O L T A G E
6 – 9 volts unfiltered DC voltage
4 Volts Peak to Peak AC Voltage
1 Second scale

6. Oscilloscope's Filtered voltage: A smooth supply of voltage.
Unfiltered voltage: Normally a ripple type wave pattern.

7. Oscilloscope's
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 -5

8. Peak to Peak voltage is determine by multiplying:
Grid division x voltage setting = Peak to peak voltage

9. Oscilloscope's
Oscilloscope can be used to measure an event over a period of time.
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.

10. Oscilloscope's To check frequency you may need some math.
Number of grid lines covered for 1 cycle divided by the time scale.

11. Wheel speed sensor
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.

12. Two ABS wave forms. Both are good the difference is the meter set-up

13. 2 V O L T
SCALE
5 mS Time Scale
NORAM ABS PATTERN

14. 2 V O L T S C
A L E
10 mS
2 Volts
10 mS Time Scale
Normal ABS Pattern

15. Throttle Position Sensor
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.

16. Normal Throttle Position Wave Form
Throttle Held open
Throttle Snapped 5 4 3 2 1
200 mS Time Division
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale

17. Defective TPS 5 4 3 2 1
200 mS Time Division
Normal Throttle Position Wave Form
Most throttle position can be easily seen on the 200 mS scale

18. Air Flow Meters
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

19. MASS AIR FLOW METER
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

20. Normal float back to match air flow
Spike due to acceleration
Throttle Released
Normal fall-off caused by inertia
Around 1 Volt at idle

21. Hot Wire Air flow Meters
Temperature stabilizes
Voltage spike due to quick throttle opening 5 4 3 2 1
Throttle Released
Cold air cooling of wire
At idle around 1 volt normal
250 mS time division

22. 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. 5 4 3 2 1
250 mS time division

23. Wave Forms 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.

24. Square Wave Normal voltage spikes 15 10 5 Normal Square wave.
Normal Square wave.
NOTE: Any wave that is on more than off or off ore than on is called a pulsed wave.

25. Pulsed Wave
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.

26. Pulsed Wave .
The difference in wave length is caused by circuit demands 20 15 10 5
Wave length
NORMAL PULSE WAVE

27. Pulsed Wave . Voltage did not drop properly 20 15 10 5 Bad pulse wave
Bad pulse wave
Voltage did increase properly

28. Coolant Temperature Sensor (CTS)
Most coolant sensors are Negative Temperature Coefficient (NTC) devices.
The sensor resistance starts out high around 200 Ohms and drops as engine temperature increases.

29. Bad CTS wave form Good CTS waveform V O L T S 5 4 3 2 1
50 second scale

30. Bad CTS wave forms
Bad CTS sensor or electrical connection disconnected waveform V O L T S 5 4 3 2 1
Bad CTS erratic voltage pattern
50 second scale

31. Crankshaft Sensor
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.
Even if the signal pattern look good.

32. Crankshaft Sensor Normal due to missing tooth on reluctor or flywheel.
The missing tooth is used by the PCM to determine crankshaft position

33. Crankshaft Sensor Voltage at start-up Voltage at higher cranking RPM
NOTE: Operating parameters vary from manufactures

34. Crankshaft Sensor
Engine Running: Note the higher voltage

35. Crankshaft Sensor
A defective crankshaft sensor will show little or no output on the oscilloscope
Proper output voltage is critical. 1 .8 .6 .4 .2
Defective Crankshaft sensor
Voltage to LOW

36. Knock Sensor 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

37. Knock Sensor Point where knock occurred 5 V 4 O 3 L 2 T 1 A G E
Point where knock occurred V O L T
A G E
NOTE: Knock sensor output should normally be zero
50 mS scale

38. Knock Sensor 5 4 3 2 1
Bad knock sensor pattern

39. Oscilloscope's
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

40. Oscilloscope's Quiz Pattern B Pattern A
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

41. Oscilloscope's Quiz 2. How many seconds pass from point A to Pont B?
4. 4 A B
1 Second Scale

42. Oscilloscope's Quiz
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 2 1 2 1

43. Oscilloscope's Quiz 4. What is peak Negative voltage in this pattern?
A. - 1 volt
B. - 2 volts
C. - 4 volts
D volts 2 1

44. Oscilloscope's Quiz 5. What is peak to peak voltage in this pattern?
A. 1 volt
B. 2 volts
C. 4 volts
D volts 2 1

45. Oscilloscope's Quiz
6. The number of complete cycles per second measured is:
A. Amperage
B. Frequency
C. Ohms
D. Voltage

46. Oscilloscope's Quiz
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

47. Oscilloscope's Quiz 8. What time scale is this oscilloscope set for?
A. 2 mS
B. 5 mS
C. 10 mS
D. 100 mS

48. Oscilloscope's Quiz
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 3 2 1
50 Second Scale

49. Oscilloscope's Quiz 10. Which diagram is of a good ground circuit?
B. 2
C. 3
D. 4 1 2 3 4