Toyota training body electrical diagnosis ch02

Technician Handbook
652 Body Electrical Diagnosis

Technical Training

47


Technician Handbook
652 Body Electrical Diagnosis

The Electrical
Wiring Diagram

The Toyota Electrical Wiring Diagram (EWD) is the roadmap to all
the electrical components and wiring in Toyota vehicles. The EWD is
not just a book of wiring diagrams, but an information resource for
anything electrical on the vehicle. The EWD includes:
•  Overall wiring diagram
•  Diagrams for every system circuit
•  Power source diagrams
•  Ground points
•  Junction block and relay locations
•  Location of components
•  Electrical wire routing
•  System operation and troubleshooting hints
•  Terms, symbols, abbreviations, and definitions
•  Information on “How to Use This Manual”

NOTE

48

For the most part, the printed EWD manual and the EWD on TIS
contain the same information. When there are differences, they will
be noted during this course. TIS, however, provides different ways
to locate information in the EWD and also provides crossreferencing to all service literature on one platform. Once you learn
how to use these features, you will find the EWD on TIS an
invaluable diagnostic tool.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

EWD Overview

The Index

Because the EWD contains so much information, it takes a little time
to learn where the information is located and what the diagrams and
symbols can tell you. We will take a detailed look at all of these
features, and how to use them in diagnosing an electrical problem.
The first page of the printed EWD is an index to all the sections of
the manual.
With the large number of pages and sections in the EWD, the fastest
way to find the diagram or information you need is to use the index.
The example illustrated here is the index for the 2010 Camry. It is
representative of all the EWDs from 1990 to present with the
following exceptions:

•  The Part Number of Connectors section was not introduced until
the 1999 model year. Prior to that year, connector part numbers
are not included in the EWD.
•  The Connector List section was not introduced until the 2000
model year. For earlier years, connectors are listed with the
system circuits to which they belong.

Technical Training

49


Technician Handbook
652 Body Electrical Diagnosis

System Circuits Index

50

The majority of your troubleshooting efforts will involve using the
system circuit diagrams. In the System Circuit Diagram section of
the printed EWD, you will find the index to the diagrams for every
circuit on the vehicle. All the other sections of the EWD provide
supporting information for these diagrams.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

EWD on TIS – 2005 MY
and Earlier

For the 2005 model year and earlier vehicles, the EWD on TIS is an
electronic version of the printed manual, containing all the same
information as the paper EWD.
Because it is an electronic version of the manual, however,
navigating the EWD is different than flipping the pages of a book.
Taking advantage of the computer’s capabilities, the EWD uses a
“tree” on the left side of the screen for primary navigation. To use
the tree, simply click on any of the titles in the list.
The tree is arranged alphabetically in several levels. The illustration
shows where the index is found – in the “General” section under
“Introduction.” On TIS, however, you would not use the index to find
what you’re looking for. You would use the tree.
Because of the different way of navigating the EWD on TIS, this
section occasionally describes how you would find information using
the tree on TIS.

Technical Training

51


Technician Handbook
652 Body Electrical Diagnosis

EWD on TIS – 2006 MY
and Later

Beginning with 2006 model year vehicles, the interface for viewing
the EWD on TIS is different. The information on TIS is the same as
in the paper EWD, but it is arranged very differently to take
advantage of the computer’s power and convenience.
In this section, you will initially learn what information is available in
the EWD and how to use it by primarily referring to the printed EWD
manual, and possibly referring to TIS for pre-2006 vehicles.
Later in this section, you will learn how to access the same
information using the EWD Viewer for 2006 MY and later vehicles.

52

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

“How to Use This Manual”

The system circuit diagrams display most of the information about
the circuit using symbols, abbreviations, and color coding. To
troubleshoot the circuit, you need to know how to read these
symbols and codes.
You will find a detailed explanation of the symbols and codes in the
“How to Use This Manual” section of the EWD (the top half is
illustrated above).
Things to note on this page:
B.  Relay blocks are noted by clear ovals with the number of the

relay block inside.
C.  Parentheses by wires indicate model specific wiring.
E.  Wiring harness connectors are illustrated by clear rectangles
with the name of the connector inside. The arrows are on the
male connector side.
J.  Junction blocks are shown as grey boxes with the connector
number inside an oval and the terminal number next to the oval.

Technical Training

53


Technician Handbook
652 Body Electrical Diagnosis

“How to Use This Manual”
(cont.)

The bottom half of the explanation for using the EWD is
illustrated above.
Things to note on this page:
H.  With shielded wires, do not pierce or attempt to splice!
J.  Terminal numbers are at the end of each wire, and the
component’s connector name is next to the component name.
K.  Ground points are shown as triangles with the ground point
name inside.
N.  Inner harness splice locations are always approximate. 2006
and later EWDs do not number or locate splices.

54

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Troubleshooting Section

The troubleshooting section provides basic information for:
•  Checking voltage
•  Checking continuity and resistance
•  Finding a short circuit
These skills are discussed in detail in this course.

Technical Training

55


Technician Handbook
652 Body Electrical Diagnosis

Connector
Repair Information

56

The Troubleshooting section of the EWD manual also contains

information on how to disconnect and reconnect connectors as well
as connector and terminal repair information.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Glossary of Terms
and Symbols

If you are looking at a system circuit and find a component you
cannot identify, refer to the Glossary of Terms and Symbols.
In the illustration, note the two types of Manual Switch – normally
open and normally closed. The state of the switch refers to its “at
rest” state in the circuit.
Looking at the three different kinds of Relay in the illustration
(normally open, normally closed, and double throw), note they are
shown with the relay coil not powered.

Technical Training

57


Technician Handbook
652 Body Electrical Diagnosis

Switch Positions

Sometimes switch positions can be confusing. You have to think
about the application to understand proper operation.
•  A stop light switch is shown as a normally open switch. It is only
open when it is installed, and the brake pedal is not depressed.
When it is not installed, it is a closed switch.
•  An AC pressure switch is shown with both switches closed. Both
switches are only closed when the switch is installed, and the
system is within normal operating pressures.

58

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Tracing Current Flow

Technical Training

When tracing current flow through a combination switch, note
the switch position, and any related circuits that may affect
component operation.

59


Technician Handbook

652 Body Electrical Diagnosis

Abbreviated Illustrations

Note that system circuit diagrams only show the parts of
components that directly relate to that circuit.
In the example above, the two switches are shown differently, but
they are actually the same component, a headlight switch:
•  The one on the left is from the headlight system circuit.
•  The one on the right is from the taillight system circuit.
Junction connectors, junction blocks, and relay blocks are other
examples of component illustrations that will only show the part of
the component affecting the circuit.

60

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Gang-type Switches

Technical Training

Look closely at components with multiple switches inside. If
they are connected by a dotted line, then the switches are tied
together and move as one (a gang-type switch).

61


Technician Handbook
652 Body Electrical Diagnosis

Use this space to write down any questions you may have for your instructor.
NOTES:

62

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Relays

Two kinds of relays used in Toyota vehicles are conventional
mechanical relays and solid state relays (shown above).
•  Mechanical relays are always shown with the coil OFF.
•  Solid state relays are always part of a relay box and are not
serviceable. (You must replace the entire relay box.)
It is important to know how solid state relays operate in order to
troubleshoot them.
•  The power source (B+) and power out are shown as 3
connectors in a row. The middle connector has a diode installed
to prevent current surges.
•  The single connection on the top turns the solid state relay ON

when it is grounded.
You have to look at the system circuit diagram and consult the
system outline in the EWD or Repair Manual to determine proper
operation for each solid state relay application.

Technical Training

63


Technician Handbook
652 Body Electrical Diagnosis

Solid State Relays

64

Solid state relays are actually transistors– miniaturized electronic
components that have a purpose similar to mechanical relays.
Transistors, like relays, allow a circuit with low current to control a
circuit with high current.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Reading the System
Circuit Diagram

System circuit diagrams contain a large amount of information, in
both written and graphical form, including:
•  Wire colors
•  Junction and relay block identification
•  Component and part identification
•  Connectors and pin numbers
•  Wire harness connectors
•  Switches and relays
•  Splice points
•  System outline and service hints
To effectively use this information you need to know the meanings of
the abbreviations and symbols. You also need to know how to use
the cross reference tables to find information in other support
sections of the EWD.

NOTE

Technical Training

The positions of switches and relays in the system circuit diagrams
are based on the vehicle being off, with no keys in the vicinity and
no one touching the vehicle.

65


Technician Handbook
652 Body Electrical Diagnosis

System Outline

NOTE
Service Hints

66

Some system circuit diagrams include a System Outline. When
troubleshooting a circuit, you should always review the System
Outline (when it is available) to help you understand how the
circuit works. This is especially important in circuits with logic
components because the internal logic is not always obvious from
the circuit diagram.
When a System Outline is not provided, use the system description
in the Repair Manual or New Car Features manual.
The system circuit diagram frequently includes Service Hints that
can be helpful in diagnosis.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Important Notes

Sometimes it’s the small things that make a big difference in
successfully troubleshooting a circuit. For example, some diagrams
include important notes.
Always read the title at the top of the diagram carefully. In some

cases you may have one circuit diagram for a “Headlight Circuit with
Daytime Running Lights,” and a another diagram for “Headlight
Circuit without Daytime Running Lights.” Trying to troubleshoot the
circuit using the wrong diagram can be frustrating.
Also watch for asterisks (*), and parentheses ( ).
•  Asterisks alert you to different wiring or connections based
upon model, engine type, California, Federal, or Canadian
specifications.
•  Parentheses are another way you may be alerted to specific
conditions or specifications.

Technical Training

67


Technician Handbook
652 Body Electrical Diagnosis

Wire Identification

Besides being shown in color, wire colors are also indicated by an
alphabetical code next to each of the wires. The first letter represents
the basic wire color, and the second letter indicates the color of the
“stripe” on the wire.
•  Color Codes
As you look at the list of color codes, note that the color blue uses
the letter “L” to distinguish it from the letter “B” used for “black.” The
color purple uses the letter “V” (for violet) to distinguish it from the
letter” P” used for pink.

•  Component Pigtails
The wire colors of component pigtails (such as on a tail lamp) are
not shown in the EWD. The colors in the EWD represent the
vehicle harness up to where it is connected to the component.
•  Silver Bands on the Wire Insulation
On some wires you will find small silver “bands.” These bands (which
are not shown on the wiring diagram) indicate that the wire uses a
PVC insulation. This insulation is lighter in weight and thinner than
the normal insulation, making the wire diameter appear smaller than
it actually is. (It may look like a 20 gauge wire on the outside, but is
really 16 gauge when the wire strands are examined.)

68

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Painted Wire Harnesses

In some newer models, a wire harness may be made completely
from white wiring, such as the 2010 Prius front door wire harness.
For wire color identification, paint stripes are applied near
connector terminals.
Wire color codes shown in the EWD are the same as other models.
Note the examples shown above for wire color identification.

Technical Training

69


Technician Handbook
652 Body Electrical Diagnosis

Shielding

Shielding is used on low voltage or low current wires such as those
for the oxygen sensor, knock sensor, and distributor G and Ne
signals. When a wire is shielded, an additional ground wire is
wrapped around the insulation of the low current wire to absorb any
electro-magnetic interference.
In the EWD, shielding is represented by a dotted line around a wire.

CAUTION

70

When checking for voltage in a circuit that uses shielded wires,
NEVER puncture the insulation with the test probe! This will
short the sensor wire to the ground wire.

Technical Training


Technician Handbook
652 Body Electrical Diagnosis

Components and
Connectors

In the system circuit diagram, all loads, relays, switches, junction
connectors, ECUs and ECU-type controllers, capacitors (noise filters),
and isolation diodes are treated as components. Components are
color coded light blue in the diagram.

Component Location

Each component is identified by a connector code and the component
name. The codes appear in a list following the diagram with a cross
reference to the page number in the Electrical Wire Routing section
which shows the component’s location in the vehicle.
Although on TIS you can find the Electrical Wire Routing section
under “Power Source/Network” in the tree, you can also go directly to
that section by clicking on the blue hyperlinked page number in the
cross reference table.

Technical Training

71