480 Auto Electricity and Electronics
Note: If you install a PROM backwards, it
may require replacement because of
physical damage.
Computer Learn Procedures
Once the computer is connected and programmed, when
necessary, it must adjust to, or “learn,” the vehicle’s sensor
inputs and to control output actuators. The computer must
receive inputs to formulate adaptive strategies to set some of its
output parameters. This is usually done by driving the vehicle
for a few minutes to allow the computer to learn the sensors and
output actuators, and to adjust system operation according to
the EEPROM programming. In a few cases, sensors or actuators
may have to be manually adjusted using a scan tool.
Summary
❑ Always start the service of a computer system with an
inspection.
❑ Most problems are caused by conventional causes.
❑ Avoid thinking “computer problem” when the engine
or another system fails to work properly. Remember
the basics!
❑ Most sensors fall into one of three categories: voltage
generating, switching, and variable resistance.
❑ You can normally use a digital VOM to measure sensor
resistance or voltage output. If not within spec limits,
something is wrong with the sensor or its wiring.
❑ Many resistance or switching sensors are fed a refer-
ence voltage (about 5 volts) by the computer. This
allows a current signal to fl ow back to the computer.
❑ Do not use a low-impedance meter or test light to
check computer system components. The current
draw through the meter or light could be high enough
to damage some electronic components.
❑ Actuator service involves testing the system solenoids,
servo motors, and displays. They can develop opens,
shorts, and other problems.
❑ The computer is one of the last components to suspect. If it
must be replaced, you must normally reuse the old PROM.
❑ Use proper techniques when replacing a PROM to
avoid damage.
Review Questions—Chapter 24
Please do not write in this text. Place your answers on a
separate sheet of paper.
1. A(n) _____ _____ involves looking for signs of
obvious trouble such as loose wires, leaking vacuum
hoses, and part damage.
2. Describe the cipet principle.
3. What are four common causes of a poor electrical
connection?
4. How is a VOM used to do a basic test on any type of
sensor?
5. What are three ways a sensor can produce signals for
a computer?
6. A bad _____ _____ sensor can keep the engine from
running because it triggers the ignition system.
7. A bad _____ _____ sensor will usually reduce engine
performance and fuel economy but will not normally
keep the engine from running.
8. Name three substances that can contaminate an
oxygen sensor.
9. Explain how to read an oxygen sensor.
10. Typically, how do you test a coolant temperature sensor?
11. Explain one way to see if an idle speed motor is
functioning.
12. In your own words, describe a few ways to fi nd out if
multipoint fuel injectors are working.
13. Explain the procedure for checking a glow plug.
14. The _____ is usually one of the last components to be
tested.
15. A computer output can be a voltage reference to a(n)
_____ or current fl ow to a(n) _____.
16. How can you save computer memory while still
disconnecting the car battery for safety?
17. In your own words, how do you replace an on-board
computer?
ASE Certifi cation-Type Questions
1. An automobile is brought into the shop with an
engine coolant temperature sensor circuit problem.
Technician A checks the wires going to this particular
sensor. Technician B performs a resistance test on the
engine coolant temperature sensor. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.
2. An automobile’s engine is misfi ring. Technician A
fi rst checks the computer and its sensor network.
Technician B fi rst checks the engine for any
mechanical or ignition system problems. Who is right?
(A) A only.
(B) B only.
(C) Both A and B.
(D) Neither A nor B.