OBJECTIVES

Automotive Electricity and Electronics, 2/eBy James D Halderman

© 2009 Pearson Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

OBJECTIVES

After studying Chapter 24, the reader should be able to:

1. Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “G” (Horn and Wiper/Washer Diagnosis and Repair) and content area “H” (Accessories Diagnosis and Repair).

2. Describe how the horn operates.3. List the components of a wiper circuit.4. Explain how the blower motor can run at different

speeds.



HORNS

• Horns are devices that emit a loud sound, and vehicles are equipped with one or two horns.

FIGURE 24-1 The two horns on this vehicle were finally located under the front bumper. They were not visible until the vehicle was hoisted.



HORNS

• With a relay, the horn button on the steering wheel or column completes a circuit to ground that closes a relay, and the heavy current flow required by the horn then travels from the relay to the horn.

FIGURE 24-2 A typical horn circuit. Note that the horn button completes the ground circuit for the relay.



HORNSHorn System Diagnosis

• There are three types of horn failure:– No horn operation– Intermittent operation– Constant operation




• If a horn does not operate at all, check for the following:– Burned fuse or fusible link– Open circuit– Defective horn– Faulty relay– Defective horn switch




• If a horn operates intermittently, check for the following:– Loose contact at the switch– Loose, frayed, or broken wires– Defective relay



HORNSHorn Service

• When a horn malfunctions, circuit tests are made to determine if the horn, relay, switch, or wiring is the source of the failure.

• Typically, a digital multimeter (DMM) is used to perform voltage drop and continuity checks to isolate the failure.



HORNSHorn Service

• Switch and relay. – A momentary contact

switch is used to sound the horn.

FIGURE 24-3 The horn switch is part of a combination switch on some vehicles.



HORNSHorn Service

• Circuit Testing. – Make sure the fuse or fusible link is good before

attempting to troubleshoot the circuit.– On a system with a relay, test the power output circuit and

the control circuit.– Test points on this system are similar to those of a system

with a relay, but there is no control circuit.



HORNSHorn Service

• Horn Replacement– To replace a horn,

simply remove the fasteners and lift the old horn from its mounting bracket.

FIGURE 24-4 Horns typically mount to be radiator core support or bracket at the front of the vehicle.



HORNSHorn Service

• Adjusting Horn Pitch– An adjusting screw that extends through the horn

housing changes the diaphragm travel to control the pitch.

FIGURE 24-5 An adjusting screw is provided for setting the horn pitch on some horns.



WINDSHIELD WIPER AND WASHER SYSTEM

• Windshield wiper systems and circuits vary greatly between manufacturers as well as between models.

• Accurate test specifications and circuit diagrams are required for diagnosing the system.




FIGURE 24-6 A circuit diagram is necessary to troubleshoot a windshield wiper problem.




• A typical combination wiper and washer system consists of the following:– Wiper motor– Gearbox– Wiper arms and linkage– Washer pump– Hoses and jets– Fluid reservoir– Combination switch




• The motor and gearbox assembly connects to the wiper switch on the instrument panel or steering column.

FIGURE 24-7 The motor and linkage bolt to the body and connect to the switch with a wiring harness.



WINDSHIELD WIPER MOTORS

• Switches in the mechanical wiper motor assembly provide the necessary operation for “parking” and “concealing” of the wipers.

FIGURE 24-8 (a) A typical wiper motor with the housing cover removed. The motor itself has a worm gear on the shaft that turns the small intermediate gear, which then rotates the gear and tube assembly, which rotates the crank arm (not shown) that connects to the wiper linkage. (b) If the brush retainer becomes loose, the wiper motor will stop because the brushes get their ground connection through the retainer and housing.




• Most wiper motors use a permanent magnet motor with a low-speed brush and a high-speed brush.

• When current flows through the high-speed brush, there are fewer turns on the armature between the hot and ground brushes, and therefore the resistance is less.

• With less resistance, more current flows and the armature revolves faster.




FIGURE 24-9 A typical wiring diagram of a two-speed windshield wiper circuit using a three-brush, two-speed motor. The dashed line for the multifunction lever indicates that the circuit shown is only a part of the total function of the steering column lever.




FIGURE 24-10 A typical wiring diagram of athree-speed windshield wiper circuit using a two-brush motor, but both a series and a shunt field coil.



WINDSHIELD WIPER MOTORSWindshield Wiper Diagnosis

• If the wiper motor does not run at all, check for the following:– Tripped circuit breaker– Grounded or inoperative switch– Defective motor– Circuit wiring fault




• If the motor operates but the wipers do not, check for the following:– Stripped gears in the gearbox– Loose or separated motor-to-gearbox connection– Loose linkage to the motor connection




• If the motor does not shut off, check for the following:– Defective parking switch inside the motor– Defective wiper switch– Poor ground connection at the wiper switch



WINDSHIELD WIPER MOTORSWindshield Wiper Testing

• When the wiper motor does not operate with the linkage disconnected, a few simple voltmeter tests quickly isolate the circuit fault.

FIGURE 24-11 A typical wiper motor connector pin chart.



WINDSHIELD WIPER MOTORSWindshield Wiper Testing

• To test the wiper system:1. Switch the ignition on and set the wiper switch to a speed at which the motor does not operate.

2. Check for battery voltage available at the appropriate wiper motor terminal for the selected speed.

3. Check that battery voltage is available at the motor side of the wiper switch.

4. Check for battery voltage available at the power input side of the wiper switch.



WINDSHIELD WIPER MOTORSWindshield Wiper Service

• Bulkhead-mounted units are accessible from under the hood, while the cowl panel is removed to service a motor mounted in the cowl.

FIGURE 24-12 The wiper motor and linkage mount under the cowl panel on many vehicles.




• Rear-window wiper motors are generally located inside the rear door panel of station wagons, or the rear hatch panel on vehicles with a hatchback or liftgate.

FIGURE 24-13 A single wiper arm mounts directly to the motor on most rear wiper applications.




• Instrument panel switches are either snap-in units or are retained by one or more screws covered by a snap-in bezel.

FIGURE 24-14 A typical instrument panel–mounted windshield wiper control switch assembly.




• Steering column wiper switches, which are operated by controls on the end of a switch stalk, require partial disassembly of the steering column for replacement.

FIGURE 24-15 The wiper switch attaches to the steering column on many vehicles.



WINDSHIELD WIPER MOTORSPulse-Wipe Systems

• Pulse-wipe systems may rely on simple electrical controls, such as a variable-resistance switch, or be controlled electronically through a control module.

FIGURE 24-16 This rain sense wiper system adjusts wiper speed based on the amount of water on the windshield.



WINDSHIELD WIPER MOTORSPulse-Wipe Systems

• A solid-state pulse-wipe timer regulates the control circuit of the pulse relay to direct current to the motor at the prescribed interval.

FIGURE 24-17 Circuit diagram of a rheostat-controlled, electronically timed interval wiper.



WINDSHIELD WIPER MOTORSWindshield Washer Diagnosis

• Inoperative windshield washers may be caused by the following:– Blown fuse– Empty reservoir– Clogged nozzle– Broken, pinched, or clogged hose– Loose or broken wire– Blocked reservoir screen– Leaking reservoir



WINDSHIELD WIPER MOTORSWindshield Washer Diagnosis

• To quick check any washer system, make sure the reservoir has sufficient fluid, then disconnect the pump hose and operate the washer switch.

FIGURE 24-18 Disconnect the hose at the pump and operate the switch to check a washer pump.



WINDSHIELD WIPER MOTORSWindshield Washer Service

• Washer motors are not repairable and are simply replaced if defective.

• Centrifugal or positive-displacement pumps are located on or inside the washer reservoir tank or cover and secured with a retaining ring or nut.

FIGURE 24-19 Washer pumps usually install into the reservoir and are held in place with a retaining ring.



RAIN SENSE WIPER SYSTEMParts and Operation

• The wiper switch can be left on the sense position all of the time and if no rain is sensed, the wipers will not swipe.

FIGURE 24-20 A typical rain sensing module located on the inside of the windshield near the inside rearview mirror.



RAIN SENSE WIPER SYSTEMParts and Operation

• The control knob is rotated to the desired wiper sensibility level.

FIGURE 24-21 The electronics in the rain sense wiper module can detect the presence of rain drops under various lighting conditions.



RAIN SENSE WIPER SYSTEMDiagnosis and Service

• If there is a complaint about the rain sense wipers not functioning correctly, check the owner’s manual to be sure that they are properly set and adjusted.

• Also, verify that the windshield wipers are functioning correctly on all speeds before diagnosing the rain sensor circuits.



BLOWER MOTOR OPERATION

• The same blower motor moves air inside the vehicle for air conditioning, heat, and defrosting or defogging.

• The switch gets current from the fuse panel with the ignition switch on, then directs full battery voltage to the blower motor for high speed and to the blower motor through resistors for lower speeds.



BLOWER MOTOR OPERATION

FIGURE 24-22 A typical squirrel cage blower motor. A replacement blower motor usually does not come equipped with the squirrel cage blower, so it has to be switched from the old motor.

FIGURE 24-23 If blower motor resistors are defective, replacement resistors are purchased as a unit, as shown.



BLOWER MOTOR DIAGNOSIS

• If the blower motor does not operate at any speed, the problem could be any of the following:

1. Defective ground wire or ground wire connection

2. Defective blower motor (not repairable; must be replaced)

3. Open circuit in the power-side circuit, including fuse, wiring, or fan switch




• If the blower motor operates normally at high speed but not at any of the lower speeds, the problem could be melted wire resistors or a defective switch.

FIGURE 24-24 A typical blower motor circuit with four speeds. The three lowest fan speeds (low, medium-low, and medium-high) use the blower motor resistors to drop the voltage to the motor and reduce current to the motor. On high, the resistors are bypassed. The “high” position on the fan switch energizes a relay, which supplies the current for the blower on high through a fusible link.




• The blower motor can be tested using a clamp-on DC ammeter.

FIGURE 24-25 Using a mini AC/DC clamp-on multimeter to measure the current draw of a blower motor.



ELECTRICAL ACCESSORY SYMPTOM GUIDE

• The following list will assist technicians in troubleshooting electrical accessory systems.









Blower Motor DiagnosisStep-by-Step



Blower Motor DiagnosisStep-by-Step cont


















SUMMARY

1. Horn frequency can range from 1,800 to 3,550 Hz.

2. Most horn circuits use a relay, and the current through the relay coil is controlled by the horn switch.

3. Most windshield wipers use a three-brush, two-speed motor.

4. Windshield washer diagnosis includes checking the pump both electrically and mechanically for proper operation.

5. Most blower motors use resistors wired in series to control blower motor speed.

6. A good blower motor should draw less than 20 A.



REVIEW QUESTIONS

1. What are the three types of horn failure?

2. Explain how the horn switch is used to operate the horn.

3. Describe how to determine if a windshield wiper problem is electrical or mechanical.

4. Explain why a defective blower motor draws more current (amperes) than a good motor.



CHAPTER QUIZ

1. Technician A says that a defective high-speed blower motor relay could prevent high-speed blower operation, yet allows normal operation at low speeds. Technician B says that a defective (open) blower motor resistor can prevent low-speed blower operation, yet permit normal high-speed operation. Which technician is correct?a) Technician A onlyb) Technician B onlyc) Both Technicians A and Bd) Neither Technician A nor B



CHAPTER QUIZ

2. To determine if a windshield wiper problem is electrical or mechanical, the service technician should _____.a) Disconnect the linkage arm from the windshield wiper

motor and operate the windshield wiper

b) Check to see if the fuse is blown

c) Check the condition of the wiper blades

d) Check the washer fluid for contamination



CHAPTER QUIZ

3. A weak-sounding horn is being diagnosed. Technician A says that a poor ground connector at the horn itself can be the cause. Technician B says an open relay can be the cause. 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

4. What controls the operation of a pulse-wiper system?a) A resistor that controls current flow to the wiper

motor

b) A solid-state (electronic) module

c) A variable-speed gem set

d) A transistor



CHAPTER QUIZ

5. Which pitch horn is used for a single horn application?a) High pitch

b) Low pitch



CHAPTER QUIZ

6. The horn switch on the steering wheel _____.a) Sends electrical power to the horns

b) Provides the ground circuit for the horn

c) Grounds the horn relay coil

d) Provides power (12 V) to the horn relay



CHAPTER QUIZ

7. A rain sense wiper system uses a rain sensor that is usually mounted _____.a) Behind the grille

b) Outside of the windshield at the top

c) Inside the windshield at the top

d) On the roof



CHAPTER QUIZ

8. Technician A says a blower motor can be tested using a fused jumper lead. Technician B says a blower motor can be tested using a clamp-on ammeter. 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

9. A defective blower motor draws more current than a good motor because _____.a) The speed of the motor increases

b) The CEMF decreases

c) The airflow slows down, which decreases the cooling of the motor

d) Both a and c



CHAPTER QUIZ

10. Windshield washer pumps can be damaged if _____.a) Pure water is used in freezing weather

b) Contaminated windshield washer fluid is used

c) Ethylene glycol (antifreeze) is used

d) All of the above are used



END

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OBJECTIVES