chap43 pps Automotive technology at University of Cambridge

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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 43, the reader should
be able to:

•

•
•

Prepare for ASE Electrical/Electronic Systems
(A6) certification test content area “F”

(Gauges, Warning Devices, and Driver
Information System Diagnosis and Repair).
Be able to identify the meaning of dash
warning symbols.
Discuss how a fuel gauge works.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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OBJECTIVES:
After studying Chapter 43, the reader should
be able to:

•
•
•

Explain how to use a service manual to
troubleshoot a malfunctioning dash
instrument.
Describe how a navigation system works.
List the various types of dash instrument
displays.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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KEY TERMS:
analog
backup camera • bulb test
cathode fluorescent lighting (CFL) • cathode ray tube
(CRT) • combination valve
electromagnetic • electronically erasable programmable
read-only memory (EEPROM)
global positioning system (GPS) • head-up display (HUD)
instrument panel (IP)
Continued
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KEY TERMS:

lane departure warning system (LDWS) • light-emitting
diode (LED) • liquid crystal display (LCD)
nonvolatile random-access memory (NVRAM)
permanent-magnet (PM) generator • phosphor • pressure
differential switch
rear park assist (RPA) • stepper motor
telltale lamp • thermoelectric
vacuum tube fluorescent (VTF) display • WOW display
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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DASH WARNING SYMBOLS
All vehicles are equipped with warning lights that are often 
confusing to drivers.

Because many vehicles are sold throughout the world, symbols 
instead of words are being used as warning lights.
See Figure 43–1 for examples and meanings of most symbols. 
Always check service information for the exact meaning on the 
vehicle being serviced.

Continued
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Figure 43–1 (a) Typical dash warning symbols and their meanings.

Due to differences in 
computer displays, the 

colors in this image 
may not exactly match 
federally mandated 
colors.

Continued
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Figure 43–1 (b) Typical dash warning symbols and their meanings (cont).

Due to differences in 
computer displays, the 
colors in this image 

may not exactly match 
federally mandated 
colors.
See the complete chart on 
Page 477 of your textbook. 
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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ANALOG DASH INSTRUMENTS
Electromagnetic dash instruments use small electromagnetic 
coils that are connected to a sending unit for such things as fuel 
level, water temperature, and oil pressure. The resistance of the 
sensor varies with what is being measured.
See Figure 43–2 for typical electromagnetic fuel gauge operation.

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Figure 43–2 Electromagnetic fuel
gauge wiring. If the sensor wire is
unplugged and grounded, the
needle should point to “E”
(empty). If the sensor wire is
unplugged and held away from
ground, the needle should point to
“F” (full).

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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COMPUTER-CONTROLLED
INSTRUMENT PANELS
Many instrument panels are operated by electronic control units that 
communicate with the engine control computer for engine data such 
as revolutions per minute (rpm) and engine temperature.
These electronic instrument panels (IPs) use the voltage change 
from varying­resistance sensors, such as that of the fuel gauge, to 
determine fuel level.
Even though the sensor in the fuel tank is the same, the display may 
be computer controlled. Because sensor inputs are Interconnected, 
the technician should always follow the factory­recommended 

diagnostic procedures. See Figure 43–3.
Continued
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Figure 43–3 Many vehicles use a computer display for many functions including trip
computers, radio, clock, and air conditioning. This vehicle is not moving and yet the engine is
running, so the fuel economy is zero.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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STEPPER MOTOR GAUGES
Most analog dash displays use a stepper motor to move the 
needle. A stepper motor is a type of electric motor that is 
designed to rotate in small steps based on the signal from a 
computer. This type of gauge is very accurate.
NOTE: Some Chrysler electronic gauge clusters can be checked by 

depressing the trip reset button and then turning the ignition switch to the 
on (key on, engine off) position. The dash display needles will be 
commanded to 1/4, 1/2, 3/4, and full positions before returning to their 
normal readings.
This test allows the service technician to check the operation of each 
individual gauge, even though replacing the entire instrument panel
cluster is usually necessary to repair an inoperative gauge.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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Find Service Information and Use It
Today’s electronic circuits are often too complex to show on a wiring
diagram. Instead, all electronics are simply indicated as a solid box with
“electronic module” printed on the diagram. Even if all electronic circuitry
was shown on the diagram, it would require the skill of an electronics
engineer to determine exactly how the
circuit was designed to work. Review the
circuit at right.
Note that the grounding for the “check oil”
dash indicator lamp is accomplished
through an electronic buffer. The exact
conditions, such as amount of time since
the ignition was shut off, are unknown to

the tech. To correctly diagnose problems
with this type of circuit, techs must read,
understand, and follow written diagnostic
procedures specified by the manufacturer.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Figure 43–4

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HEAD UP DISPLAY
The head­up display (HUD) is a supplemental display that 
projects the vehicle speed and sometimes other data, such as turn 
signal information, onto the windshield. The projected image 
looks as if it is some distance ahead, making it easy for the driver 

to see without having to refocus on a closer dash display.
See Figures 43–5 and 43–6.
The head­up display can also have the brightness controlled on 
most vehicles that use this type of display. The HUD unit is 
installed in the instrument panel (IP) and uses a mirror to project 
vehicle information onto the inside surface of the windshield.
See Figure 43–7.
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Figure 43–5 A typical head-up display
showing zero miles per hour, which is
actually projected on the windshield

from the head-up display in the dash.

Figure 43–6 The dash-mounted control for
the head-up display on this Cadillac allows
thedriver to move the image up and down
on the windshield for best viewing.

Continued
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Figure 43–7 A typical head-up display (HUD) unit.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition

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NIGHT VISION
Parts and Operation  Night vision systems use a camera capable 
of observing objects in the dark to assist the driver at night. 
Primary night viewing illumination devices are the headlights.
The night vision option uses a head­up display (HUD) to improve 
the vision of the driver beyond the scope of the headlights. Using a 
HUD display allows drivers to keep their eyes on the road and 
hands on the wheel for maximum safety.
Besides the head­up display, the night vision camera uses a special 
thermal imaging or infrared technology. The camera is mounted 
behind the grill in the front of the vehicle.
See Figure 43–8.

Continued
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Figure 43–8 A night vision camera in the front of a Cadillac.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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The camera creates pictures based on heat energy emitted by objects 
rather than light reflected on an object. The image looks like a 
black­and­white photo negative when hot objects (higher thermal 
energy) appear; cool objects appear dark or black. Other parts of the 
night vision system include:
On/Off and Dimming Switch—This allows the driver to adjust 
the brightness of the display and to turn it on or off as needed.
Up/Down Switch—The night vision HUD system has an electric 
tilt adjust motor that allows the driver to adjust the image up or 
down on the windshield within a certain image.
CAUTION: Becoming accustomed to night vision can be difficult and 
may take several nights to get used to looking at the head­up display.

Continued
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Diagnosis and Service  Verify the concern, check manual or 
service information for the proper operation. Cadillac night vision 
system requires the following actions to function:
1.
2.
3.
4.

The ignition has to be in the on (run) position.
The Twilight Sentinel photo cell must indicate that it is dark.
The headlights must be on.
The switch for the night vision system must be on and the 
brightness adjusted so the image is properly displayed.

Night vision uses a camera in the front of the vehicle protected from 
debris by a grille. Small stones or other debris can get past the grille 

and damage the camera. If damaged, it must be replaced as an 
assembly because no separate parts are available.

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DASH INSTRUMENT DIAGNOSIS
With electromagnetic gauges, if the resistance of the sensor is 
low, the meter reads low. If the resistance of the sensor is high, 
the meter reads high.
NOTE: Thermoelectric gauges are opposite from electromagnetic

gauges and read low when resistance is high. The following procedures
are given for electromagnetic gauges and should be reversed for working

on thermoelectric gauges.

When troubleshooting a fuel gauge, if power is unplugged from the 
tank unit with ignition on, the dash unit should move toward full 
(high resistance). If the power lead is touched to ground (low 
resistance), the fuel gauge should register empty. The same can be 
used with oil pressure and water temperature gauges.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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TELLTALE LAMPS
Telltale lamps (often called idiot lights) warn the driver of system failure. 
Whenever the ignition is turned on, all warning lamps come on as a bulb check.
The charging system­warning

lamp may be labeled “CHARGE,”
“GEN,” or “ALT” and will light
if the charging system fault is
detected. 

Figure 43–9 This symbol is used to represent a charging circuit problem.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
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OIL PRESSURE WARNING DEVICES
The oil pressure lamp operates through use of an oil pressure 
sensor unit, which is screwed into the engine block and which 
grounds the electrical circuit and lights the dash warning lamp in 
the event of low oil pressure:

(3 to 7 PSI [20 to 50 kilopascals, kPa]). 
Figure 43–10 This oil pressure grounding switch (sending unit) has a fixed contact connected to
ground and a contact that is moved by the pressure-sensitive diaphragm.

Continued
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Normal oil pressure is generally between
10 and 60 PSI (70 and 400 kPa). 

Figure 43–11 A typical oil pressure-sending unit provides a
varying amount of resistance as engine oil pressure changes.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition

By James D. Halderman

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