© 2008 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458 Automotive...

© 2008 Pearson Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

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


1

start




2

• Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A ” (General Electrical/Electronics System Diagnosis).

• Draw the symbols used on schematics.

• Discuss the various methods that can be use to locate a short circuit.

• List the electrical troubleshooting diagnosis steps.

After studying Chapter 36, the reader should be able to:

OBJECTIVES:




3

double-pole, double-throw switch (DPDT) • double-pole, single-throw switch (DPST)

gauss gauge • momentary switch

normally closed (N.C.) • normally open (N.O.) • poles

relay • short circuit • single-pole, double-throw switch (SPDT) • single-pole, single-throw switch (SPST)

terminal • throws • tone generator tester

wiring schematic

KEY TERMS:




4

WIRING SCHEMATICS

Manufacturers’ service manuals include wiring schematics of all the electrical circuits of a vehicle. A wiring schematic, called a diagram, shows electrical components and wiring using symbols and lines to represent components and wires.

A typical wiring schematic may include all of the circuits combined on several large fold-out sheets, or they may be broken down to show individual circuits.

All circuit schematics or diagrams include the power-side wiring of the circuit and all splices, connectors, electrical components, and ground return paths.

Gauge and color of wiring are included on most wiring diagrams.Continued




5

Circuit Information Many wiring schematics include numbers and letters near components and wires that may confuse readersof the schematic. Most letters used near or on a wire identify the color or colors of the wire. The first coloror color abbreviation is the color of theinsulation, the second color is the colorof the strip or tracer on the base color.

Continued

Figure 36–1 The center wire is a solid color wire, meaning that the wire has no other identifying tracer or stripe color. The two end wires could be labeled “BRN/WHT,” indicating a brown wire with a white tracer or stripe.

Chart on Page 370 of your textbook.




6

Figure 36–2Typical section of a wiring diagram. Notice that the wire color changes at connection C210. The “.8” represents the metric wire size in square millimeters.

Shown here is a rear side-marker bulb circuit diagram where “.8 ” indicates the metric wire gauge size in square millimeters (mm2)and “PPL ” indicates a solid purple wire.

The diagram also shows the color of the wire changes at C210. This stands for “connector #210” and is used for reference purposes, and can vary depending on the manufacturer.

Continued

The color change from purple (PPL) to purple with a white tracer (PPL/WHT) is not important except to know where the wire changes color in the circuit. Wire gauge remained the same on both sides of the connection




7

Electrical and electronic symbols used in wiring & circuit diagrams.

See the chart on Page 371 of your textbook.

Figure 36–3 This figure shows typical electrical and electronic symbols used in automotive wiring and circuit diagrams.




8

Wiring diagrams indicate connections by symbols that look like arrows.Do not read these “arrows” as pointers showing the direction of currentflow. Also observe that the power side (positive side) of the circuit is usually the female end of the connector.

If a connector becomes disconnected, it will be difficult for the circuit to become shorted to ground or to another circuit because the wire is recessed inside the connector.

Wiring diagrams indicate connections by symbols that look like arrows.Do not read these “arrows” as pointers showing the direction of currentflow. Also observe that the power side (positive side) of the circuit is usually the female end of the connector.

If a connector becomes disconnected, it will be difficult for the circuit to become shorted to ground or to another circuit because the wire is recessed inside the connector.

Read The Arrows

Figure 36–4In this typical connector, note that the positive terminal is usually a female connector.




9

SCHEMATIC SYMBOLS

Schematic drawings replace photos, or line drawings of actual components with a symbol that represents the actual component:

Continued

Figure 36–5 The symbol for a battery. The positive plate of a battery is represented by the longer line and the negative plate by the shorter line. The voltage of the battery is usually stated next to the symbol.

Battery The plates of a battery are represented by long and short lines. The longer line represents the positive plate of a battery and the shorter line represents the negative plate of the battery. Each pair of short and long lines represents one cell of a battery.




10

Because each cell of a typical automotive lead-acid battery has 2.1 volts, a battery symbol showing a 12-volt battery should have six pairs of lines. However, most symbols simply use two or three pairs of long and short lines and list battery voltage next to the symbol.

The positive terminal of the battery is indicated with a plus sign (+), representing the positive post of the battery, placed next to the long line of the end cell. The negative (ground) terminal is represented by a negative sign (–) and is placed next to the shorter cell line.

Figure 36–6The ground symbol on the left represents earth ground. The ground symbol on the right represents a chassis ground.

Continued




11

Wiring Electrical wiring is shown as straight lines with a few numbers and/or letters to indicate:

Continued

Wire size—This can be either AWG, such as 18 gauge or in square millimeters, such as 0.8.

Circuit numbers—Each wire in part of a circuit is labeled with the circuit number to help the service tech trace the wiring and allows for an explanation of how the circuit is supposed to work.

Wire color—Most schematics also indicate an abbreviation for the color of the wire and place it next to the wire. Many wires have two colors: a solid color and a stripe color. In this case, the solid color is listed, and then a dark slash (/) and the color of the stripe is listed. For example, red/wht would indicate a red wire with a white tracer.

See Figure 36–7.




12

Figure 36–7 Starting at the top, the wire from the ignition switch is attached to terminal B of connector C2, the wire is 0.5 mm 2 (20-gauge AWG) and is yellow. The circuit marker is 5. The wire enters connector C202 at terminal B3.

Continued




13

Terminals—The metal part attached at the end of a wire is called a terminal. A symbol for a terminal is shown in Figure 36–8.

Wire connections—When two wires are electrically connected, the junction is shown with a black dot. See Figure 36–9.

When two wires cross in a schematic that are not electrically connected, one of the wires is shown as going over the other wire and does not connect. See Figure 36–10.

Connectors—An electrical connector is a plastic part that contains one or more terminals. While the terminals provide the electrical connection in a circuit, it is the plastic connector that keeps the terminals together mechanically.

Continued




14

Figure 36–8The electrical terminals are usually labeled with a letter, as shown on this cooling fan motor.

Figure 36–9Two wires that cross at the dot indicate that the two are electrically connected.

Figure 36–10Wires that cross, but do not electrically contact each other, are shown with one wire bridging over the other.

Continued




15

Connections are usually labeled with a “C ” and three numbers which indicate the general location of the connector.

Connector numbers represent the general area of the vehicle.

100 to 199 Under the hood

200 to 299 Under the dash

300 to 399 Passenger compartment

400 to 499 Rear package or trunk area

500 to 599 Left-front door

600 to 699 Right-front door

700 to 799 Left-rear door

800 to 899 Right-rear door

Even-numbered connectors are on the right (passenger side) of the vehicle, odd-numbered connectors on the left (driver’s side).

Continued




16

Figure 36–11Connectors (C), grounds (G), and splices (S) are followed by a number, generally indicating the location in the vehicle. For example, G209 is a ground connection located under the dash.

C-102 is a connector located under the hood (between 100 and 199) on the right side of the vehicle (even number 102).

Continued




17

Figure 36–12 The ground for the battery is labeled G305 indicating the ground connector is located in the passenger compartment of the vehicle. The ground wire is black (BLK), the circuit number is 50, and the wire is 32 mm 2 (2-gauge AWG).

Grounds and Splices—Grounds and splices are also labeled using the same general format as connectors.

A ground located under thedash on the driver’s sidecould be labeled G-201(G means ground).

A splice indication is an “S” followed by three numbers,such as S-301.

Continued




18

Electrical Components Most components have their own unique symbol that shows basic function or parts.

Continued

Bulbs—Light bulbs usually use a filament, which heats and then gives off light when electrical current flows. The symbol used for a light bulb shows a circle with a filament inside. A dual-filament bulb, such as is used for taillights and brake light/turn signals, is shown with two filaments.

Figure 36–13 The symbol for light bulbs shows the filament inside a circle, which represents the glass ampoule of the bulb.




19

Electric Motors An electric motor symbol shows a circle with the letter “M ” in the center and two electrical connections, one to the top and one at the bottom. See Figure 36–14 for an example of a cooling fan motor.

Resistors Usually part of another component, the symbol does appear on many schematics and wiring diagrams. A resistor symbol is a jagged line representing resistance to current flow.

If the resistor is variable, such as a Thermistor, an arrow is shown running through the symbol of a fixed resistor.

A potentiometer is a three-wire variable resistor and it is shown with an arrow pointing toward the resistance part of a fixed resistor.

See Figure 36–15Continued




20

Figure 36–14 An electric motor symbol shows a circle with the letter “M ” in the center and two black sections that represent the brushes of the motor. This symbol is used even though the motor is a cross-flow design.

Figure 36–15Resistor symbols vary depending on the type of resistor.

Continued




21

A two-wire rheostat is usually shown as part of another unit, such as a fuel level sending unit.

Continued

Figure 36–16 A rheostat uses just two wires—one is connected to a voltage source and the other is attached to the movable arm.




22

Capacitors Usually part of an electronic component and not a replaceable component. Older vehicles used capacitors to reduce radio interference. They were installed inside alternators or attached to wiring connectors. See Figure 36–17.

Electric Heated Unit Electric grid-type rear window defoggers and cigarette lighters are shown in a square box-type symbol.Figure 36–18.

Boxed Components If a component is shown in a box using a solid line, the box is the entire component. If a box uses dashed lines, it represents a part of a component. A commonly used dashed-line box is a fuse panel. Often, just one or two fuses are shown in a dashed-line box, meaning the fuse panel has more fuses than shown.

See Figures 36–19 and 36–20.Continued




23

Figure 36–17Symbols used to represent capacitors. If one of the lines is curved, this indicates that the capacitor being used has a polarity, while the one without a curved line can be installed in the circuit without concern about polarity.

Figure 36–18The grid-like symbol represents an electrically heated element.

Continued




24

Figure 36–20A solid box representsan entire component.

Figure 36–19A dashed outline represents a portion (part) of a component.

Continued




25

Separate Replaceable Part Often components shown on a schematic cannot be replaced but are part of a complete assembly. On a schematic of GM vehicles, the following is shown:

Continued

If a part name is underlined, it is a replaceable part.

If a part is not underlined, it is not available as a replaceable part, but is rather included with other components shown and sold as an assembly.

If the case itself is grounded,the ground symbol is attachedto the component as shown.

Figure 36–21This symbol represents a component that is case grounded.




26

Switches Electrical switches are drawn on a wiring diagram in their normal position. This can be one of two possible positions:

Continued

Normally open The switch is not connected to a terminal and no current flows in this position. This type of switch is labeled N.O.

Normally closed The switch is electrically connected to a con-tact and current will flow through the switch. This type of switch is labeled N.C.

NOTE: All switches are shown on schematics in their normal position.This means that the headlight switch will be shown normally off, as aremost other switches and controls.

NOTE: All switches are shown on schematics in their normal position.This means that the headlight switch will be shown normally off, as aremost other switches and controls.




27

Other switches can use more than two contacts.

The poles refer to the number of circuits completed by the switch and the throws refer to the number of output circuits. A single-pole, single-throw (SPST) switch has only two positions—on or off.

A single-pole, double-throw (SPDT) switch has three terminals—one wire in and two wires out. A headlight dimmer switch is an example of a typical SPDT switch. In one position, the current flows to the low-filament headlight; in the other, the current flows to the high-filament headlight.

There are also double-pole, single-throw (DPST) switches and double-pole, double-throw (DPDT) switches.

See Figure 36–22.Continued




28

Figure 36–22 (a) A symbol for a single-pole, single-throw (SPST) switch. This type of switch is normally open (N.O.) because nothing is connected to the terminal that the switch is contacting in its normal position. (b) A single-pole, double-throw (SPDT) swtich has three terminals. (c) A double-pole, single-throw (DPST) swtch has two positions (off and on) and can control two separate circuits. (d) A double-pole, double-throw (DPDT) switch has six terminals—three for each pole. Note: “c ” and “d ” also show a dotted line between the two arms indicating that they are mechanically connected.

(a) (b) (c) (d)

Continued




29

Another type of switch that is used on most vehicles is called a momentary switch. Usually used to send a voltage signal to a module or controller to request a device be turned on or off.

The switch just makes momentary contact and returns to the open position. The symbol that represents a momentary switch uses two dots for the contact with a switch above them.

A momentary switch, for example, can be used to lock or unlock a door or to turn the air conditioning on or off. If the device is currently operating, the signal from the momentary switch will turn it off, and if it is off, the switch will signal the module to turn it on.

An advantage of momentary switches is they can be very lightweight and small. Most momentary switches use a membrane constructed of foil and plastic.




30

RELAY TERMINAL IDENTIFICATION

A relay is a magnetic switch that uses a movable armature to control a heavy electrical load by using a low-amperage electrical switch. Most automotive relays adhere to common terminal identification.

Relays are found in many circuits because they are capable of being controlled by computers, yet are able to handle enough current to power motors and accessories.

See Figures 36–23 and 36–24.

Continued




31

Figure 36–23 A relay uses a movable arm to complete a circuit whenever there is a power at terminal 86 and a ground at terminal 85. A typical relay only requires about 1/10 ampere through the relay coil. The movable arm then closes the contacts (#30 to #87) and can relay 30 amperes or more.

Continued




32

Figure 36–24 A cross-sectional view of a typical four-terminal relay. Current flowing through the coil (terminals 86 and 85) causes the movable arm (called the armature) to be drawn toward the coil magnet. The contact points complete the electrical circuit connected to terminals 30 and 87.

Continued




33

A coil that provides magnetic pull to a movable armature (arm). The resistance of most relay coils ranges from 50 to 150 ohms, but is usually between 60 and 100 ohms. The International Standard Organization (ISO) identification of the coil terminals are 86 and 85. Terminal number 86represents power to the relay coil85 represents the ground side.

Continued

Figure 36–25A typical relay showing the schematic of the wiring in the relay. Terminals #30 and #87 are electrically connected when the relay is energized.

The relay coil can be controlled bysupplying either power or groundto the relay coil winding.

Most relays use four or five terminals as follows:




34

The higher amperage current flow through a relay flows through terminals 30 and 87 and often 87a. Terminal 30 is usually where power is applied. When the relay is at rest without power and ground to the coil, the armature inside the relay electrically connects terminals 30 and 87a if the relay has five terminals.

When there is power at terminal 86 and a ground at terminal 85 of the relay, a magnetic field is created in the coil winding, which draws the armature of the relay toward the coil. The armature, when energized electrically, connects terminals 30 and 87.

The maximum current through the relay is determined by the resistance of the circuit and relays are designed to safely handle the designed current flow.

See Figures 36–26 and 36–27.Continued




35

Figure 36–26 All schematics are shown in their normal, nonenergized position.

Continued

Figure 36–27 A typical horn circuit. Note that the relay contacts supply the heavy current to operate the horn when the horn switch simply completes a low current circuit to ground, causing the relay contacts to close.




36

Relay Voltage Spike Control Relays contain a coil and whenever power is removed, the magnetic field surrounding the coil collapses, creating a voltage to be induced in the coil winding.

Figure 36–28 When the relay or solenoid coil current is turned off, the stored energy in the coil forward biases the clamping diode and effectively reduces voltage spike.

This induced voltage can be as high as 100 volts or more and can cause problems with other electronic devices in the vehicle. The short high-voltage surge can be heard as a “pop ” in the radio.

To reduce the induced voltage, some relays contain a diode connected across the coil inthe reverse bias direction.

Continued




37

Most relays use a resistor connected in parallel with the coil winding. The use of a resistor, typically about 400 to 600 ohms, reduces the voltage spike by providing a path for the voltage created in the coil to flow back through the coil windings whenthe coil circuit is opened.

Continued

Figure 36–29A resistor used in parallel with the coil windings is a commonly used spike reduction method used in many relays.




38

COMMON POWER OR GROUND

Whenever diagnosing an electrical problem that affects more than one component or system, check the electrical schematic for a common power source or a common ground.

Under-hood light

Inside lighted mirrors

Dome light

Left-side courtesy light

Right-side courtesy light

For a customer complaint involving one or more of the items listed, check the fuse and the common part of the circuit that feeds all of affected lights. Check for a common ground if several components that seem unrelated are not functioning correctly.

Continued

See Figure 36–30 for an example where all of the following lights are powered by one fuse (power source).




39

Figure 36–30A typical wiring diagram showing multiple switches and bulbs powered by one fuse.

Schematic on Page 376 of your textbook.




40

Often, a customer will notice just one fault while other lights or systems may not be working correctly. For example, a customer noticed that the electric mirrors stopped working. The service technician checked all electrical components in the vehicle and discovered that the interior lights were also not working.

Often, a customer will notice just one fault while other lights or systems may not be working correctly. For example, a customer noticed that the electric mirrors stopped working. The service technician checked all electrical components in the vehicle and discovered that the interior lights were also not working.

Check Everything

The interior lights were not mentioned by the customer as being a problem most likely because the driver only used the vehicle in daylight hours.

The service technician found the interior light and power accessory fuse blown. Replacing the fuse restored the proper operation of the electric outside mirror and the interior lights.

However, what caused the fuse to blow? A visual inspection of the dome light, next to the electric sunroof, showed an area where a wire was bare. Evidence was seen where the bare wire had touched the metal roof, which could cause the fuse to blow. The technician covered the bare wire with a section of vacuum hose and then taped the hose with electrical tape to complete the repair.




41

Often the owners of vehicles, especially of pickup trucks and sport utility vehicles (SUVs), want to add additional electrical accessories or lighting.

It is tempting in these cases to simply splice into an existing circuit.

However, whenever another circuit or component is added, the current that flows through the newly added component is also added to the current for the original component.

This additional current can easily overload the fuse and wiring. Do not simply install a larger-amperage fuse; the wire gauge size was not engineered for the additional current and could overheat.

The solution is a relay, which uses a small coil to create a magnetic field that causes a movable arm to switch on a higher-current circuit.

Often the owners of vehicles, especially of pickup trucks and sport utility vehicles (SUVs), want to add additional electrical accessories or lighting.

It is tempting in these cases to simply splice into an existing circuit.

However, whenever another circuit or component is added, the current that flows through the newly added component is also added to the current for the original component.

This additional current can easily overload the fuse and wiring. Do not simply install a larger-amperage fuse; the wire gauge size was not engineered for the additional current and could overheat.

The solution is a relay, which uses a small coil to create a magnetic field that causes a movable arm to switch on a higher-current circuit.

Do It Right—Install a Relay - Part 1




42

The typical relay has 50 to 150 ohms (usually 60 to 100) of resistance and requires just 0.24 to 0.08 amp when connected to a 12-volt source. This small additional current will not be enough to overload the existing circuit.

The typical relay has 50 to 150 ohms (usually 60 to 100) of resistance and requires just 0.24 to 0.08 amp when connected to a 12-volt source. This small additional current will not be enough to overload the existing circuit.

Do It Right—Install a Relay - Part 2

Figure 36–31 To add additional lighting, simply tap into an existing light wire and connect a relay. Whenever the existing light is turned on, the coil of the relay is energized. The arm of the relay then connects power from another circuit (fuse) to the auxiliary lights without overloading the existing light circuit.




43

USING SCHEMATICS FOR TROUBLESHOOTING

Follow these steps when troubleshooting wiring problems.

Step #1 Verify the malfunction. If, for example, the backup lights do not operate, make certain that the ignition is on (key on, engine off), with the gear selector in reverse, and check for operation of the backup lights.

Step #2 Check everything that does or does not operate correctly. If the taillights are also failing to operate, the problem could be a loose or broken ground connection in the trunk area that is shared by both the backup lights and the taillights.

Step #3 Check the fuse for the backup lights. See Figure 36–32.

Continued




44

Figure 36–32 Always check the simple things first. Check the fuse for the circuit you are testing. Maybe a fault in another circuit controlled by the same fuse could have caused the fuse to blow. Use a test light to check that both sides of the fuse have voltage.

Step #4 Check for voltage at the backup light socket. This can be done using a test light or a voltmeter.

If voltage is available at the socket, the problem is either a defective bulb or a poor ground at the socket or a ground wire connection to the body or frame.

If no voltage is available at the socket, consult a wiring diagram.

The wiring diagram should show all of the wiring and components included in the circuit.




45

The common question is, where does a technician start troubleshooting when using a wiring diagram (schematic)?The common question is, where does a technician start troubleshooting when using a wiring diagram (schematic)?

Where to Start?

If the circuit contains a relay, start your diagnosis at the relay.The entire circuit can be tested at the terminals of the relay.

The easiest first step is to locate the unit on the schematic thatis not working at all or not working correctly.

Often a ground is used by more than one component. Therefore,ensure that everything else is working correctly. If not, then thefault may lie at the common ground (or power) connection..

Divide the circuit in half by locating a connector or a part of thecircuit that can be accessed easily. Then check for power andground at this midpoint. This step could save you much time.

HINT 1

HINT 2

HINT 3

a. Trace where the unit gets its ground connection.b. Trace where the unit gets its power connection.




46

LOCATING A SHORT CIRCUIT

A short circuit usually blows a fuse, and a replacement fuse often also blows in the attempt to locate the source of the short circuit.

A short circuit is an electrical connection to another wire or to ground before the current flows through some or all of the resistance in the circuit. A short-to-ground will always blow a fuse and usually involves a wire on the power side of the circuit coming in contact with metal.

A short-to-voltage may or may not cause the fuse to blow and usually affects another circuit. Look for areas of heat or movement where two power wires could come in contact with each other.

Continued




47

Several methods can be used to locate the short.

Fuse Replacement Method Disconnect one component at a time and replace the fuse. If the new fuse blows, continue the process until the location of the short is determined. This method uses many fuses and is not a preferred method for finding a short circuit.

Circuit Breaker Method Connect an automotive circuit breaker to contacts of the fuse holder with alligator clips. Circuit breakers are available that plug directly into the fuse panel, replacing a blade-type fuse. The circuit breaker will alternately open and close the circuit, protecting the wiring from damage while still providing current flow through the circuit.

NOTE: A heavy-duty (HD) flasher can also be used in place of a circuitbreaker to open and close the circuit. Wires and terminals must be madeto connect the flasher unit where the fuse normally plugs in.

NOTE: A heavy-duty (HD) flasher can also be used in place of a circuitbreaker to open and close the circuit. Wires and terminals must be madeto connect the flasher unit where the fuse normally plugs in.




48

All components in the defective circuit should be disconnected one at a time until the circuit breaker stops clicking. The unit that was disconnected and stopped the circuit breaker clicking is the unit causing the short circuit.

If the circuit breaker continues to click with all circuit components unplugged, the problem is in the wiring from the fuse panel to any one of the units in the circuit.

Test Light Method Remove the blown fuse and connect a test light to the terminals of the fuse holder. If there is a short, current will flow from the power side of the fuse holder through the test light to ground through the short circuit, and the test light will light.

Unplug connectors or components protected by the fuse until the test light goes out.

Continued




49

Ohmmeter Method The recommended method of finding a short.An ohmmeter indicates low ohms when connected to a short circuit. The correct procedure for locating a short using an ohmmeter:

CAUTION: Connecting the lead to the power side of the fuse holder will cause current flow through and damage to the ohmmeter.CAUTION: Connecting the lead to the power side of the fuse holder will cause current flow through and damage to the ohmmeter.

1. Connect one lead of an ohmmeter (set to a low scale) to a good clean metal ground and the other lead to the circuit side of the fuse holder.

2. The ohmmeter will read zero or almost zero ohms if the circuit is shorted.

3. Disconnect one component in the circuit at a time and watch the ohmmeter. If the ohmmeter reading goes to high ohms or infinity, the component just unplugged caused the short circuit.

Continued




50

Gauss Gauge Method A special pulsing circuit breaker (similar to a flasher unit) can be installed in place of the fuse. Current will flow through the circuit until the circuit breaker opens the circuit.

As soon as the circuit breaker opens the circuit, it closes again. This on-and-off current flow creates a pulsing magnetic field around the wire carrying the current. A Gauss gauge is a handheld meter that responds to weak magnetic fields.

This pulsing magnetic field will register on the Gauss gauge even through the metal body of the vehicle. A needle-type compass can also be used to observe the pulsing magnetic field.

See Figures 36–33 and 36–34.

Continued




51

Figure 36–33 (a) After removing the blown fuse, a pulsing circuit breaker is connected to the terminals of the fuse. (b) The circuit breaker causes current to flow, then stop, then flow again, through the circuit up to the point of the short-to-ground. By observing the Gauss gauge, the location of the short is indicated near where the needle stops moving due to the magnetic field created by the flow of current through the wire.

Continued




52

Figure 36–34 A Gauss gauge can be used to determine the location of a short circuit even behind a metal panel.

A Gauss gauge is used to observe a pulsing magnetic field, which is indicated onthe gauge as needle movement.

Continued




53

Electronic Tone Generator Tester An electronic tone generator tester can be used to locate a short-to-ground or an open circuit. Similar to test equipment used to test telephone and cable television lines, a tone generator tester generates a tone that can be heard through a receiver (probe).

Figure 36–35 A tone generator-type tester used to locate open circuits and circuits that are shorted-to-ground. Included with this tester is a transmitter (tone generator), receiver (probe), and headphones for use in noisy shops.

The tone will be generated while there is a continuous electrical path along the circuit. The signal will stop if there is an open (break) or short-to-ground in the circuit.

The windings in the solenoids and relays will increase the strength of the signal in these locations.

See Figures 36–36 and 36–37. Continued




54

Figure 36–36 To check for a short-to-ground using a tone generator, connect the black transmitter lead to a good chassis ground and the red lead to the load side of the fuse terminal. Turn the transmitter on and check for tone signal with the receiver. Using a wiring diagram, follow the strongest signal to the short-to-ground. There will be no signal beyond the fault.

Continued




55

Figure 36–37 To check for an open (break), connect the red lead of the tone generator to the load side of the fuse terminal and the black lead to a good chassis ground. Turn on the transmitter an then listen for the tone signal with the receiver set in the open position. Using a wiring diagram, follow the signal along the circuit until the tone stops, indicating the location of the open.




56

Electrical shorts are commonly caused either by movement, which causes the insulation around the wiring to be worn away, or by heat melting the insulation. When checking for a short circuit, first check the wiring that is susceptible to heat, movement, and damage:

Electrical shorts are commonly caused either by movement, which causes the insulation around the wiring to be worn away, or by heat melting the insulation. When checking for a short circuit, first check the wiring that is susceptible to heat, movement, and damage:

Heat or Movement

1. Heat. Wiring near heat sources, such as the exhaust system, cigarette lighter, or generator.

2. Wire movement. Wiring that moves, such as in areas near the doors, trunk, or hood.

3. Damage. Wiring subject to mechanical injury, such as in the trunk, where heavy objects can move around and smash or damage wiring. This can also occur as a result of an accident or a previous repair.




57

Intermittent electrical problems are common yet difficult to locate. To help locate these hard-to-find problems, try operating the circuit and then start wiggling the wires and connections that control the circuit.

If in doubt where the wiring goes, try moving all the wiring starting at the battery. Pay particular attention to wiring running near the battery or the windshield washer container. Corrosion can cause wiring to fail, and battery acid fumes and alcohol-based windshield washer fluid can start or contribute to the problem.

If you notice any change in the operation of the device being tested while wiggling the wiring, look closer in the area you were wiggling until the actual problem is located and corrected.

Intermittent electrical problems are common yet difficult to locate. To help locate these hard-to-find problems, try operating the circuit and then start wiggling the wires and connections that control the circuit.

If in doubt where the wiring goes, try moving all the wiring starting at the battery. Pay particular attention to wiring running near the battery or the windshield washer container. Corrosion can cause wiring to fail, and battery acid fumes and alcohol-based windshield washer fluid can start or contribute to the problem.

If you notice any change in the operation of the device being tested while wiggling the wiring, look closer in the area you were wiggling until the actual problem is located and corrected.

Wiggle Test




58

ELECTRICAL TROUBLESHOOTING GUIDE

1. For a device to work, it must have power and ground.

2. If there is no power to a device, an open power side (blown fuse, etc.) is indicated.

3. If there is power on both sides of a device, an open ground is indicated.

4. If a fuse blows immediately, a grounded power-side wire is indicated.

5. Most electrical faults result from heat or movement.

6. Most noncomputer-controlled devices operate by opening and closing the power side of the circuit (power-side switch).

7. Most computer-controlled devices operate by opening and closing the ground side of the circuit (ground-side switch).




59

The following procedure has been field tested for many years and provides a step-by-step guide to follow when troubleshooting:

STEP-BY-STEP TROUBLESHOOTING PROCEDURE

1. Determine the customer concern (complaint) and get as much information as possible from the customer or service advisor.

a. When did the problem start?

b. Under what conditions does the problem occur?

c. Have there been any recent repairs to the vehicle which could have created the problem?

2. Verify the customer’s concern by actually observing the fault.

HINT: Split the circuit help isolate the problem and start at the relay.HINT: Split the circuit help isolate the problem and start at the relay.




60

3. Perform a thorough visual inspection and be sure to check everything that does and does not work.

4. Check for technical service bulletins (TSBs).

5. Check the factory service information and follow the troubleshooting procedure.

a. Determine how the circuit works

b. Determine which part of the circuit is good, based on what works and what does not work

c. Isolate the problem area

6. Determine the root cause and repair the vehicle.

7. Verify the repair and complete the repair order (R.O.) by listing the three C’s (complaint, cause, and correction).




61

A customer complained that after driving for a while, he got a static shockwhenever the door handle was grabbed when exiting the vehicle. The customer thought that there must be an electrical fault and that the shock was coming from the vehicle itself. In a way, the shock was caused by the vehicle, but it was not a fault.

A customer complained that after driving for a while, he got a static shockwhenever the door handle was grabbed when exiting the vehicle. The customer thought that there must be an electrical fault and that the shock was coming from the vehicle itself. In a way, the shock was caused by the vehicle, but it was not a fault.

Shocking Experience

The service technician sprayed the cloth seats and carpet with an antistatic spray and the problem did not reoccur.

Obviously, a static charge was being created by movement of the driver’s clothing on the seats and discharged when the driver touched the metaldoor handle.

Figure 36–38 Antistatic spray can be used to stop customers from being shocked when they touch a metal object like the door handle.




62

SUMMARY

Continued

1. Most wiring diagrams include the wire color, circuit number, and wire gauge.

2. The number used to identify connectors, grounds, and splices usually indicates where they are located in the vehicle.

3. All switches and relays shown on a schematic are shown in their normal position either normally closed (N.C.) or normally open (N.O.).




63

SUMMARY

4. A short-to-voltage affects the power side of the circuit and usually involves more than one circuit.

5. A short-to-ground usually causes the fuse to blow and usually affects only one circuit.

6. Most electrical faults are a result of heat or movement.

(cont.)




64

end

© 2008 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458 Automotive...

Documents

Transcript of © 2008 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ 07458 Automotive...