422 Section 4 Computer Control Technology
Summary
❚ Pinpoint tests are specifi c tests of individual com-
ponents. They are completed after scanning for
trouble codes.
❚ A preliminary inspection involves looking for
signs of obvious trouble: loose wires, leaking vac-
uum hoses, part damage, etc.
❚ Semiconductors are very easy to damage. They
can be damaged by static electricity, voltage
spikes, heat, and impact shocks.
❚ Stress testing refers to the use of heat, cold, or
moisture to simulate extreme operating conditions
of components, like an electronic control unit.
❚ Poor electrical connections are the most common
cause of electrical-related problems in a computer
system.
❚ Vacuum leaks are frequently caused by deterio-
rated, broken, or loose vacuum hoses. Vacuum
leaks often make a hissing sound.
❚ A reference voltage (typically 5 volts) is fed to
switching and variable resistance type sensors.
❚ Sensor sockets have a deep pocket and a cutout
for a sensor pigtail (wires).
❚ Since they contain movable contact points, relays
are a common source of computer system problems.
❚ Computer service usually involves a few tests
and computer replacement if needed.
❚ Some computers use the old PROM (memory
chip) during computer replacement, since it stores
data for the specifi c make and model vehicle.
Technical Terms
Write the defi nitions for the following terms on a
separate sheet of paper.
Activities
1. Describe and sketch the procedure you
would use to test a temperature sensor for
proper operation.
2. Demonstrate two methods of checking a
knock sensor—with a multimeter and by
manual tapping.
3. Look up vehicle software update on the
Internet. Try to fi nd which cars sometimes
require computer reprogramming. Write a
paragraph on your fi ndings.
Review Questions
Answer the following questions using the
information provided in this chapter .
l. What should you look for during a
preliminary inspection of a computer
system?
2. Explain fi ve questions you should ask
yourself when analyzing computer system
problems.
3. How can a vacuum leak upset the
operation of a computer system?
4. An engine runs poorly only when cold.
Symptoms and a trouble code indicate
a problem with the engine coolant
temperature sensor. Technician A says to
measure the engine coolant temperature
sensor’s resistance with a digital ohmmeter
while measuring coolant temperature with
a digital thermometer. Technician B says
to measure the sensor’s ac voltage output
while measuring its temperature with a
digital thermometer. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.
5. How do you check sensor reference voltage?
6. Explain three ways to test an active sensor.
7. Describe three ways to test an actuator.
8. Relays are a common source of problems in
a modern computer system. True or false?
9. How do you save computer memory?
actuator service
basic circuit problem
carrier
computer output
computer service
intermittent
junction block
memory saver
pin number
pinpoint test
poor electrical
connection
preliminary visual
inspection
reference mark
relay tester
relearn procedure
schematic
sensor service
sensor socket
stress testing
updated PROM
vacuum leak