OBJECTIVES

2. OBJECTIVES After studying Chapter 24, the reader should be able to: • 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). • Describe how the horn operates. • List the components of a wiper circuit. • Explain how the blower motor can run at different speeds.

3. 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.

4. 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.

5. HORNSHorn System Diagnosis • There are three types of horn failure: • No horn operation • Intermittent operation • Constant operation

6. HORNSHorn System Diagnosis • 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

7. HORNSHorn System Diagnosis • If a horn operates intermittently, check for the following: • Loose contact at the switch • Loose, frayed, or broken wires • Defective relay

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. WINDSHIELD WIPER AND WASHER SYSTEM FIGURE 24-6 A circuit diagram is necessary to troubleshoot a windshield wiper problem.

15. WINDSHIELD WIPER AND WASHER SYSTEM • 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

16. WINDSHIELD WIPER AND WASHER SYSTEM • 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.

17. 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.

18. WINDSHIELD WIPER MOTORS • 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.

19. WINDSHIELD WIPER MOTORS 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.

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

21. 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

22. WINDSHIELD WIPER MOTORSWindshield Wiper Diagnosis • 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

23. WINDSHIELD WIPER MOTORSWindshield Wiper Diagnosis • 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

24. 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.

25. 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.

26. 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.

27. WINDSHIELD WIPER MOTORSWindshield Wiper Service • 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.

28. WINDSHIELD WIPER MOTORSWindshield Wiper Service • 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.

29. WINDSHIELD WIPER MOTORSWindshield Wiper Service • 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.

30. 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.

31. 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.

32. 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

33. 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.

34. 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.

35. 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.

36. 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.

37. 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.

38. 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.

39. 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.

40. 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

41. BLOWER MOTOR DIAGNOSIS • 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.

42. BLOWER MOTOR DIAGNOSIS • 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.

43. ELECTRICAL ACCESSORY SYMPTOM GUIDE • The following list will assist technicians in troubleshooting electrical accessory systems.

44. ELECTRICAL ACCESSORY SYMPTOM GUIDE

45. ELECTRICAL ACCESSORY SYMPTOM GUIDE

46. Blower Motor DiagnosisStep-by-Step

47. Blower Motor DiagnosisStep-by-Step cont

48. Blower Motor DiagnosisStep-by-Step cont

49. Blower Motor DiagnosisStep-by-Step cont

50. Blower Motor DiagnosisStep-by-Step cont