1. Sensors
Chapter Lesson 3

2. Computer System Operation
There are three stages of computer system operation:
input
processing and storage
output

3. Inputs and Outputs

4. Computer System Block Diagram
Fig 18

5. Sensors
Most vehicle sensors, or transducers, change a physical condition into an electrical signal
Transduce:
to change from one form to another

6. Sensor Locations Sensors can be found almost anywhere on a vehicle:
on the engine
on or in the transmission or transaxle
in the exhaust system
on the wheel hubs
on and in the fuel tank
on the suspension
in the trunk

7. Some of the sensors located on the engine and transaxle
Sensor Locations
Some of the sensors located on the engine and transaxle

8. Sensor Classifications
Sensors can be classified into two general categories:
active sensors
passive sensors

9. Active Sensor Produces its own voltage signal internally
The signal is fed to the computer for analysis
Shielded wire may be used to block induced voltage and interference in the signal wire(s)

10. Active Sensor

11. Passive Sensor Variable resistance sensor
Voltage is fed to the sensor from the computer
Sensor resistance varies with changes in a condition
temperature, pressure, motion, etc
As sensor resistance changes, the voltage signal sent back to the computer changes

12. Passive Sensor

13. Types of Sensors

14. Variable Resistor Sensor
Changes its resistance with a change in condition
temperature, pressure, etc
Throttle position and temperature sensors are variable resistance sensors

15. Switching Sensor
Opens or closes the sensor circuit to provide an electrical signal
Used to detect almost any condition
Produces a digital signal
Transmission pressure switches are switching sensors

16. Magnetic Sensor Also called a permanent magnet (PM) generator
Uses part movement and induced current to produce a signal
Produces an analog signal
Used to monitor speed or part rotation
Vehicle speed and wheel speed sensors are often magnetic sensors

17. Hall-Effect Sensor
Uses a special semiconductor chip to sense part movement and speed
Produces a digital signal
Applications:
crankshaft position sensors
camshaft position sensors
distributor pickup devices

18. Uses a semiconductor chip that reacts to magnetic fields
Hall-Effect Sensor
Uses a semiconductor chip that reacts to magnetic fields

19. Optical Sensor
Uses light-emitting diodes and photo diodes to produce a digital signal
Used to sense part rotation and speed
Used in some distributors and as speed sensors mounted outside the speedometer

20. A reverse-biased photodiode conducts current when exposed to light
Optical Sensor
A reverse-biased photodiode conducts current when exposed to light

21. Piezoelectric Sensor Generates voltage from a physical shock or motion
An internal crystal produces a voltage signal proportional to the amount of vibration detected
Used to sense abnormal engine vibration caused by engine knock
knock sensor

22. Piezoelectric Sensor

23. Solar Sensor Converts sunlight directly into an electrical signal
Made of a semiconductor material that converts photons into direct current

24. Solar Sensor

25. Direction Sensor Detects the polarity of a moving magnet
Signals which direction a part is rotating
Used in some computer-controlled steering systems

26. Reference Voltage Applied to a passive sensor by the computer
5 volts on most vehicles
The computer steps down battery voltage so that a smooth, constant supply of dc voltage is fed to the sensor
The sensor changes its internal resistance to alter the reference voltage

27. Sensor Types Common sensors used in late-model vehicles:
Intake air temperature sensor (IAT)
measures the temperature of intake air as it enters the intake manifold
Engine coolant temperature sensor (ECT)
measures the temperature of engine coolant

28. Sensor Types Oxygen sensors Manifold absolute pressure sensor (MAP)
measure the amount of oxygen in the engine’s exhaust gases
Manifold absolute pressure sensor (MAP)
measures pressure inside the intake manifold
Barometric pressure sensor (BARO)
measures the outside air pressure

29. Sensor Types Throttle position sensor (TP) Engine speed sensor
measures the opening angle of the throttle valves to detect driver power demand
Engine speed sensor
measures engine rpm
Crankshaft position sensor (CKP)
measures crankshaft position and speed

30. Sensor Types Camshaft position sensor (CMP) Mass airflow sensor (MAF)
measures camshaft position and rotation
Mass airflow sensor (MAF)
measures the amount of intake air flowing into the engine
Knock sensor (KS)
detects engine pinging, preignition, or detonation

31. Sensor Types Transaxle/transmission sensor Brake switch
checks transaxle or transmission gear selection
Brake switch
detects brake pedal application
Wheel speed sensor
measures wheel rotational speed for anti-lock brake and traction control application

32. Sensor Types Oil level sensor EGR sensor Impact sensors
measures the amount of oil in the engine oil pan
EGR sensor
measures the position of the exhaust gas recirculation valve pintle
Impact sensors
detect a collision

33. Sensor Types Vehicle speed sensor (VSS) Fuel tank pressure sensor
measures the vehicle’s road speed
Fuel tank pressure sensor
measures fuel tank pressure as part of some evaporative emission control systems
Battery temperature sensor
monitors battery temperature so the computer can adjust charging system output as needed

34. Circuit Sensing
Involves using the computer itself to monitor component and circuit operation
Computer monitors current flow through various circuits to diagnose:
fuel injectors
ignition coil action
computer operation