Diagnosis and Troubleshooting of Automotive Electrical, Electronic, and Computer Systems, Fifth...

Diagnosis and Troubleshooting of Automotive Electrical,Electronic, and Computer Systems, Fifth EditionBy James D. Halderman

© 2010 Pearson Higher Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES

After studying Chapter 23, the reader should be able to:

1. Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “F” (Gauges,Warning Devices, and Driver Information System Diagnosis and Repair).

2. Discuss how a fuel gauge works.

3. Explain how to use a service manual to troubleshoot a malfunctioning dash instrument.

4. Describe how a navigation system works.

5. List the various types of dash instrument displays.



ANALOG DASH INSTRUMENTS

• Two basic types of analog (needle-type) dash instrument gauges used on older vehicles were the electromagnetic and the thermoelectric gauges.



ANALOG DASH INSTRUMENTSThermoelectric Gauges• This type of gauge moves very slowly, which is an

advantage, because turns and hills do not affect the readings of the fuel gauge, for example, and the needle tends to remain steady.

FIGURE 23-1 A thermoelectric fuel gauge has 5 volts coming from the instrument voltage regulator (IVR). The IVR is shared by all other dash instruments. Electronic gauges use the same sensor (sending unit) but use electronic circuits to control needle movement or digital display.



ANALOG DASH INSTRUMENTSThermoelectric Gauges• If all dash instruments are

functioning incorrectly, as when all are reading high or low, the usual cause is the instrument voltage regulator located on the back of the instrument panel.

FIGURE 23-2 Instrument voltage regulator. Vibrating points maintain current through the instrument at 5 volts. The radio choke prevents radio interference created by the pulsing current low.



ANALOG DASH INSTRUMENTSElectromagnetic Gauges• 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.



ANALOG DASH INSTRUMENTSElectromagnetic Gauges

FIGURE 23-3 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).



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.

FIGURE 23-4 Many vehicles use a computer display for certain 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.



FIND SERVICE INFORMATION AND USE IT

• Today’s electronic circuits are often too complex to show on a wiring diagram.

• Even if all electronic circuitry was shown on the wiring diagram, it would require the skill of an electronics engineer to determine exactly how the circuit was designed to work.



FIND SERVICE INFORMATION AND USE IT

FIGURE 23-5 The ground for the “check oil” indicator lamp is controlled by the electronic low-oil buffer. Even though this buffer is connected to an oil level sensor, the buffer also takes into consideration the amount of time the engine has been stopped and the temperature of the engine. The only way to properly diagnosea problem with this circuit is to use the procedures specified by the vehicle manufacturer. Besides, only the engineer that designed the circuit knows for sure how it issupposed to work.



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.



HEAD-UP DISPLAY

• The head-up 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.



HEAD-UP DISPLAY

FIGURE 23-6 A typical head-up display showing zero miles per hour, which is actually projected on the windshield from the head-up display inthe dash.

FIGURE 23-7 The dash-mounted control for the head-up display on this Cadillac allows the driver to move the image up and down on the windshield for best viewing.



HEAD-UP 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.

FIGURE 23-8 A typical HUD unit.



NIGHT VISIONParts and Operation• Night vision systems

use a camera that is capable of observing objects in the dark to assist the driver while driving at night.

• The camera is mounted behind the grill in the front of the vehicle.

FIGURE 23-9 A night vision camera in the front of a Cadillac.



NIGHT VISIONParts and Operation• 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.



NIGHT VISIONDiagnosis and Service• The first step when diagnosing a fault with the night

vision system is to verify the concern. • For example, the Cadillac night vision system

requires the following actions to function.– 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.



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.



TELLTALE LAMPS

• Telltale lamps (often called idiot lights) warn the driver of system failure.

• When the ignition is turned on, all warning lamps come on as a bulb check.

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

FIGURE 23-10 This symbol is used to represent a charging circuit problem.



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 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 23-11 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.



OIL PRESSURE WARNING DEVICES

• Normal oil pressure is generally between 10 and 60 psi (70 and 400 kPa).

FIGURE 23-12 A typical oil pressure sending unit provides a varying amount of resistance as engine oil pressure changes.



OIL PRESSURE WARNING DEVICESOil Pressure Lamp Diagnosis

• To test the operation of the oil pressure warning circuit, unplug the wire from the oil pressure sending unit, usually located near the oil filter, with the ignition switch on.

FIGURE 23-13 A Ford oil pressure sending unit. Most oil pressure sending units are located near the oil filter and are threaded into an oil gallery.



TEMPERATURE LAMP DIAGNOSIS

• Always check the cooling system operation and the operation of the warning lamp circuit when the hot lamp comes on during normal driving.

FIGURE 23-14 Temperature grounding switches expose a bimetallic strip to engine coolant temperature to light a high-temperature lamp or both high- and low-temperature warning lamps.



BRAKE WARNING LAMP

• All vehicles sold in the United States after 1967 must be equipped with a dual braking system and a dash-mounted warning lamp to signal the driver of a failure in one part of the hydraulic brake system.

FIGURE 23-15 Typical red brake warning lamp.



BRAKE WARNING LAMP

• If there is unequal hydraulic pressure in the braking system, the switch usually grounds the 12 volt lead at the switch and the lamp comes on.

FIGURE 23-16 Typical brake warning light switch located on or near the master brake cylinder.



BRAKE WARNING LAMP

• The red brake warning lamp also can be turned on if the brake fluid is low.

FIGURE 23-17 The red brake warning lamp can be turned on if the brake fluid level is low.



DIGITAL ELECTRONIC DASH OPERATION

• Mechanical or electromechanical dash instruments use cables, mechanical transducers, and sensors to operate a particular dash instrument.

• Electronic dash display systems may use one or more of the several types of displays: light-emitting diode (LED), liquid crystal display (LCD), vacuum tube fluorescent (VTF), and cathode ray tube (CRT).



DIGITAL ELECTRONIC DASH OPERATIONLED Digital Displays

• All diodes emit some form of energy during operation; the light-emitting diode (LED) is a semiconductor that is constructed to release energy in the form of light.

FIGURE 23-18 (a) Symbol and line drawing of a typical light emitting diode (LED). (b) Grouped in seven segments, this array is called a seven segment LED display

with a common anode (positive connection). The dash computer toggles the cathode (negative) side of each individual segment to display numbers and letters.

(c) When all segments are turned on, the number 8 is displayed.



DIGITAL ELECTRONIC DASH OPERATIONLiquid Crystal Displays• Liquid crystal displays (LCDs) can be arranged

into a variety of forms, letters, numbers, and bar graph displays.

• The light from a very bright halogen bulb behind the LCD shines through those segments of the LCD that have been polarized to let the light through, which then show numbers or letters.



DIGITAL ELECTRONIC DASH OPERATIONVacuum Tube Fluorescent Displays• The vacuum tube fluorescent (VTF) display is a

popular automotive and household appliance display because it is very bright and can easily be viewed in strong sunlight.

• Most VTF displays are green for best viewing under most lighting conditions.



DIGITAL ELECTRONIC DASH OPERATIONCathode Ray Tube

• A cathode ray tube (CRT) dash display, which is similar to a television tube or LCD display, permits the display of hundreds of controls and diagnostic messages in one convenient location.

FIGURE 23-19 A typical navigation system. This Acura system incorporates some of the climate control functions as well as the trip information on the display. This particular unit uses a DVD unit in the trunk along with a global positioning satellite (GPS) to display a map and your exact location for the entire country.



DIGITAL ELECTRONIC DASH OPERATION Cold Cathode Fluorescent Displays• Cold cathode fluorescent lighting (CFL) models

are used by many vehicle manufacturers for backlighting.

• CFL is replacing conventional incandescent light bulbs.



DIGITAL ELECTRONIC DASH OPERATIONElectronic Analog Displays

• A scan tool often is needed to diagnosis the operation of a computer-controlled analog dash instrument display.

FIGURE 23-20 (a) View of the vehicle dash with the instrument cluster removed. Sometimes the dash instruments can be serviced by removingthe padded dash cover (crashpad) to gain access to the rear of the dash. (b) The front view of the electronic analog dash display. (c) The rear view of the dash display showing that there are a few bulbs that can be serviced, but otherwise the unit is serviced as an assembly.



DIGITAL ELECTRONIC DASH OPERATIONOther Electronic Gauge Displays• Oil pressure, water temperature, and voltmeter

readings are other commonly used electronic dash displays.

• A warning lamp is often part of the electronic circuits in the electronic display to warn the driver of high or low battery voltage.



DIGITAL ELECTRONIC DASH OPERATIONThe WOW Display• When a vehicle equipped with a digital dash is

started, all segments of the electronic display are turned on at full brilliance for 1 or 2 seconds.

• Technicians can also use the WOW display to determine if all segments of the electronic display are functioning correctly.



THE BULB TEST

• Many ignition switches have six positions.

FIGURE 23-21 Typical ignition switch positions. Notice the bulb check position between on (run) and start.

FIGURE 23-22 Many newer vehicles place the ignition switch on the dash and incorporate antitheft controls. Note the location of the accessory position.



ELECTRONIC SPEEDOMETERS

• Electronic dash displays ordinarily use an electric vehicle speed sensor driven by a small gear on the output shaft of the transmission.

FIGURE 23-23 Permanent magnet (PM) generator vehicle speed sensor. The unit is usually driven by a gear on the output section of the transmission or transaxle.



ELECTRONIC ODOMETERS

• A small electric motor called a stepper motor is used to turn the number wheels of a mechanical-style odometer.

• A pulsed voltage is fed to this stepper motor, which moves in relation to the miles traveled.

FIGURE 23-24 Some vehicles that use a PM generator for a vehicle speed sensor use a stepper motor to drive a mechanical odometer. The stepper motor receives a signal (pulses) from the vehicle computer and rotates in “steps”corresponding to the distance to the distance traveled.



ELECTRONIC SPEEDOMETER AND ODOMETER SERVICE• If the speedometer and odometer fail to operate, the

speed sensor should be the first item checked.• If the speedometer and odometer fail to operate, the

speed sensor should be the first item checked.



ELECTRONIC FUEL-LEVEL GAUGES

• Electronic fuel-level gauges ordinarily use the same fuel tank sending unit as that used on conventional fuel gauges.

• The only difference between a digital fuel level gauge and a conventional needle type is in the display.

FIGURE 23-25 A typical fuel pump and fuel-level gauge module. The float moves against a resistor and changes the resistance of the circuit with the fuel level.



WHY DOES THE OIL PRESSURE GAUGE ON MY FORD ALWAYS READ IN THE MIDDLE?

• Some Ford Motor Company vehicles (and perhaps others) use an analog oil pressure display that is set to read in the middle of the scale as long as there is a minimum oil pressure.

FIGURE 23-26 (a) A Ford dash display with the key on, engine off. (b) As soon as the engine starts, the oil pressure gauge goes immediately to the midpoint on the gauge. This seems stranger to some vehicle owners.




• The older-style gauge used a variable-resistance oil pressure sending unit.

FIGURE 23-27 A typical magnetic and pressure gauge circuit. Notice that the oil pressure gauge reading depends on the resistance of the sensor. The lower the resistance, the higher the oil pressure on most Ford vehicles.




• On newer models, Ford started using an oil pressure switch that electrically grounds the oil pressure gauge through a 20 ohm resistor when the oil pressure is above 4.5 to 7.5 psi.

FIGURE 23-28 When the oil pressure exceeds 4.5 to 7.5 psi, the oil pressure switch closes and the meter reads in about the middle of its range due to the fixed 20 ohm resistor in the meter circuit.



NAVIGATION AND GPS

• The global positioning system (GPS) uses 24 satellites in orbit around the earth to provide signals for navigation devices.

FIGURE 23-29 Global positioning systems use 24 satellites in high earth orbit whose signals are picked up by navigation systems. The navigation system computer then calculates the location based on the position of the satellite overhead.



NAVIGATION AND GPSBackground• The current GPS was developed in the 1980s after

a civilian airplane from Korean Airlines, Flight 007, was shot down after it had gone over Soviet territory in 1983.

• Until 2000, nonmilitary use of GPS was purposely degraded by a computer program called selection availability (S/A) built into the satellite transmission signals.



NAVIGATION AND GPSNavigation System Parts and Operation• The navigation controller located in the rear of the

vehicle uses other sensors, including a digitized map to display the location of the vehicle.– GPS satellite signals– Yaw sensor– Vehicle speed sensor– Audio output/input



NAVIGATION AND GPSNavigation System Parts and Operation• Navigation systems

include the following components:

1. Screen display

2. GPS antenna

3. Navigation control unit that usually has a DVD with the map information

FIGURE 23-30 The navigation control unit is located in the trunk of this Acura.



NAVIGATION AND GPSNavigation System Parts and Operation• The DVD includes street names and the following:

1. Points of interest (POI).

2. Business addresses and telephone numbers as well as hotels and restaurants.

3. Turn-by-turn directions can be provided to addresses that are selected by:

• Points of interest (POI)

• Typed in using a keyboard shown on the display



NAVIGATION AND GPSNavigation System Parts and Operation• The navigation unit

then often allows the user to select the fastest way to the destination, as well as the shortest way, or how to avoid toll roads.

FIGURE 23-31 A typical navigation display showing various options. Some systems do not allow access to these functions if the vehicle is in gear and/or moving.



NAVIGATION AND GPSDiagnosis and Service• For the correct functioning of the navigation system,

three inputs are needed.– Location– Direction– Speed



NAVIGATION AND GPSDiagnosis and Service• The following symptoms may occur and be a

customer complaint.– If the vehicle icon jumps down the road, a fault with the

vehicle speed (VS) sensor input is usually indicated.– If the icon rotates on the screen, but the vehicle is not

being driven in circles, a fault with the yaw sensor or yaw sensor input to the navigation controller is indicated.

– If the icon goes off course and shows the vehicle on a road that it is not on, a fault with the GPS antenna is indicated.



NAVIGATION AND GPSDiagnosis and Service• Sometimes the

navigation system itself will display a warning that views from the satellite are not being received.

FIGURE 23-32 A screen display of a navigation system that is unable to acquire usable signals from GPS satellites.



ONSTARParts and Operation• OnStar is a system that includes the following

functions.1. Cellular telephone

2. Global positioning antenna and computer



ONSTARParts and Operation• Early versions used a

handheld cellular telephone, and later units used a group of three buttons mounted on the inside rearview mirror and a hands-free cellular telephone.

FIGURE 23-33 The three-button OnStar control on the inside rearview mirror. The left button (telephone handset icon) indicates hands-freecellular call. The center button contacts an OnStar advisor and the right emergency button requests that help be sent to the vehicle’s location.



ONSTARParts and Operation• The OnStar system includes the following features,

which can vary depending on the level of service desired and will affect the cost per month.– Automatic notification of airbag deployment.– Stolen vehicle location assistance.– Remote door unlock.– Roadside assistance.– Accident assistance.– Remote horn and lights.– Vehicle diagnosis.



ONSTARDiagnosis and Service• The OnStar system can fail to meet the needs of the

customer if any of the following conditions occur.1. Lack of cellular telephone service in the area

2. Poor global positioning system (GPS) signals, which can prevent an OnStar advisor from determining the position of the vehicle

3. Transport of the vehicle by truck or ferry so that it is out of contact with the GPS satellite system in order for an advisor to properly track the vehicle



BACKUP CAMERAParts and Operation• Many vehicles

equipped with navigation systems today include a backup camera for added safety while backing.

FIGURE 23-34 A typical view displayed on the navigation screen from the backup camera.



BACKUP CAMERAParts and Operation• The backup camera

used contains a wide-angle or fisheye lens to give the largest viewing area.

FIGURE 23-35 A typical fisheye-type backup camera usually located near the center on the rear of the vehicle near the license plate.



BACKUP CAMERADiagnosis and Service• The main input to the display unit comes from the

transmission range switch which signals the backup camera when the transmission is shifted into reverse.

• To check the transmission range switch, check the following:

1. Check if the backup (reverse) lights function when the gear selector is placed in reverse with the ignition on engine off (KOEO).2. Check that the transmission/transaxle is fully engaged in reverse when the selector is placed in reverse.



BACKUP CAMERADiagnosis and Service• The remaining diagnosis involves the following

visual inspection.1. Check the backup camera for damage.

2. Check the screen display for proper operation.

3. Check that the wiring from the rear camera to the body is not cut or damaged.



BACKUP SENSORSComponents• The system used in General Motors vehicles is

called rear park assist (RPA) and includes the following components.– Ultrasonic object sensors built into the rear bumper

assembly– A display with three lights usually located inside the

vehicle above the rear window and visible to the driver in the rearview mirror

– An electronic control module that uses an input from the transmission range switch and lights the warning lamps needed when the vehicle gear selector is in reverse



BACKUP SENSORSOperation• The following lights are

displayed depending on the distance from the rear bumper.– One amber lamp will light

when the vehicle is in reverse and traveling at less than 3 mph (5 km/h) and the sensors detect an object 5 ft to 40 in. from the rear bumper.

FIGURE 23-36 A typical backup sensor display located above the rear window inside the vehicle. The warning lights are visible in the inside rearview mirror.



BACKUP SENSORSOperation

– Two amber lamps light when the distance between the rear bumper and an object is between 20 and 40 in. (50 and 100 cm) and the chime will sound again.

– Two amber lamps and the red lamp light and the chime sounds continuously when the distance between the rear bumper and the object is between 11 and 20 in. (28 and 50 cm).



BACKUP SENSORSOperation• The ultrasonic sensors

embedded in the rear bumper “fire” individually every 150 ms (27 times per second).

FIGURE 23-37 The small round buttons in the rear bumper are ultrasonic sensors used to sense distance to an object.



BACKUP SENSORSOperation• The sensors fire and then receive a return signal

and arm to fire again in sequence from the left sensor to the right sensor.

• Each sensor has three wires.1. An 8 volt supply wire from the RPA module used to power the sensor

2. A reference low or ground wire

3. A signal line used to send and receive commands to and from the RPA module



BACKUP SENSORSDiagnosis• The rear parking assist control module is capable of

detecting faults and storing diagnostic trouble codes (DTCs).

• Most systems use the warning lights to indicate trouble codes.



LANE DEPARTURE WARNING SYSTEMParts and Operation• The lane departure warning system (LDWS) uses

cameras to detect if the vehicle is crossing over lane marking lines on the pavement.

• If the cameras detect that the vehicle is starting to cross over a lane dividing line, a warning chime will sound or a vibrating mechanism mounted in the driver’s seat cushion is triggered on the side where the departure is being detected.



LANE DEPARTURE WARNING SYSTEM Diagnosis and Service• Before attempting to service or repair a lane

departure warning system fault, check service information for an explanation on how the system is supposed to work.

• After a visual inspection, follow the vehicle manufacturer’s recommended diagnosis procedures to locate and repair the fault in the system.



ELECTRONIC DASH INSTRUMENT DIAGNOSIS AND TROUBLESHOOTING• If one or more electronic dash gauges do not work

correctly, first check the WOW display that lights all segments to full brilliance when the ignition switch is first switched on.

• All dash instruments except the voltmeter use a variable-resistance unit as a sensor for the system being monitored.



ELECTRONIC DASH INSTRUMENT DIAGNOSIS AND TROUBLESHOOTING• Most new-vehicle dealers are required to purchase essential

test equipment, including a test unit that permits the technician to insert various fixed-resistance values in the suspected circuit.

• If this type of special test equipment is not available, the electronic dash instruments can be tested using the following procedure.

1. With the ignition switched off, unplug the wire(s) from the sensor for the function being tested.

2. With the sensor wire unplugged, turn the ignition switch on and wait until the WOW display stops.

3. Turn the ignition switch off.



ELECTRONIC DASH INSTRUMENT DIAGNOSIS AND TROUBLESHOOTING Testing Results

• If the electronic display functions fully on and fully off with the sensor unplugged and then grounded, the problem is a defective sensor.

• If the electronic display fails to function fully on and fully off when the sensor wire(s) are opened and grounded, the problem is usually in the wiring from the sensor to the electronic dash or it is a defective electronic cluster.



MAINTENANCE REMINDER LAMPS

• Maintenance reminder lamps indicate that the oil should be changed or that other service is required.

• For example, to reset the oil service reminder light on many General Motors vehicles, you have to perform the following:

Step 1 Turn the ignition key on (engine off).

Step 2 Depress the accelerator pedal three times and hold it down on the fourth.

Step 3 When the reminder light flashes, release the accelerator pedal.

Step 4 Turn the ignition key to the off position.

Step 5 Start the engine and the light should be off.



FUEL GAUGE DIAGNOSISStep-by-Step



FUEL GAUGE DIAGNOSISStep-by-Step cont



SUMMARY

1. Most digital and analog (needle-type) dash gauges use variable-resistance sensors.

2. Dash warning lamps are called telltale lamps.

3. Many electronically operated or computer-operated dash indicators require that a service manual be used to perform accurate diagnosis.

4. Permanent magnet (PM) generators produce an AC signal and are used for vehicle speed and wheel speed sensors.



REVIEW QUESTIONS

1. Explain the difference between thermoelectric and electromagnetic dash instruments.

2. Describe LED, LCD, VTF, and CRT dash displays.

3. Discuss how to diagnose a problem with a red brake warning lamp.

4. Explain how to test the dash unit of a fuel gauge.



CHAPTER QUIZ

1. Two technicians are discussing a fuel gauge on a General Motors vehicle. Technician A says that if the ground wire connection to the fuel tank sending unit becomes rusty or corroded, the fuel gauge will read lower than normal. Technician B says that if the power lead to the fuel tank sending unit is disconnected from the tank unit and grounded (ignition on), the fuel gauge should go to empty. Which technician is correct?

a) Technician A only

b) Technician B only

c) Both Technicians A and B

d) Neither Technician A nor B



CHAPTER QUIZ

2. If an oil pressure warning lamp on a vehicle is on all the time, yet the engine oil pressure is normal, the problem could be _____.a) A defective (shorted) oil pressure sending unit (sensor)

b) A defective (open) oil pressure sending unit (sensor)

c) An open wire between the sending unit (sensor) and the dash warning lamp

d) Both b and c



CHAPTER QUIZ

3. When the oil pressure drops to between 3 and 7 psi, the oil pressure lamp lights by _____.a) Opening the circuit

b) Shorting the circuit

c) Grounding the circuit

d) Conducting current to the dash lamp by oil



CHAPTER QUIZ

4. A brake warning lamp on the dash remains on when the ignition is on. If the wire to the pressure differential switch (usually a part of a combination valve or built into the master cylinder) is unplugged, the dash lamp goes out. Technician A says that this is an indication of a fault in the hydraulic brake system. Technician B says that the problem is probably due to a stuck parking brake cable switch. Which technician is correct?

a) Technician A only






CHAPTER QUIZ

5. A customer complains that every time the lights are turned on in the vehicle, the dash display dims. What is the most probable explanation?a) Normal behavior for LED dash displays

b) Normal behavior for VTF dash displays

c) Poor ground in lighting circuit causing a voltage drop to the dash lamps

d) Feedback problem most likely caused by a short-to-voltage between the headlights and dash display



CHAPTER QUIZ

6. Technician A says that LCDs may be slow to work at low temperatures. Technician B says that an LCD dash display can be damaged if pressure is exerted on the front of the display during cleaning. Which technician is correct?a) Technician A only






CHAPTER QUIZ

7. Technician A says that backup sensors use LEDs to detect objects. Technician B says that a backup sensor will not work correctly if the paint is thicker than 0.006 in. Which technician is correct?a) Technician A only






CHAPTER QUIZ

8. Technician A says that metal-type window tinting can affect the navigation system. Technician B says most navigation systems require a monthly payment for use of the GPS satellite. Which technician is correct?a) Technician A only






CHAPTER QUIZ

9. Technician A says that the data displayed on the dash can come from the engine computer. Technician B says that the entire dash assembly may have to be replaced even if just one unit fails. Which technician is correct?a) Technician A only






CHAPTER QUIZ

10.If the vehicle icon on a navigation screen jumps down the road while driving, this is an indications of a fault with _____.a) vehicle speed (VS) input signal or sensor

b) navigation display fault

c) defective yaw sensor

d) defective GPS antenna



END

Diagnosis and Troubleshooting of Automotive Electrical, Electronic, and Computer Systems, Fifth...

Documents

Transcript of Diagnosis and Troubleshooting of Automotive Electrical, Electronic, and Computer Systems, Fifth...