Automotive Service Technology Section C/Automotive Special Problems
Course HS Title:
Automobile Service Technology/Special Problems
KCTCS Courses included in HS Title: (Lesson is prepared for course highlighted.)
KCTCS Course No.
KCTCS Course Title
This lesson will instruct the student on how to diagnose (troubleshoot) incorrect operation of motor-driven accessory circuits, and determine necessary action. Knowledge of these techniques and the skills required to correct problems associated with this task are necessary for a student to acquire if they wish to compete for high paying, high skilled jobs in an Automotive Repair Facility. Entry level technicians need to be able to perform this task to 100% accuracy. Incorrectly performing this task can lead to an automobile accident or create customer satisfaction issues.
Given the proper tools and instruction, the student will be able to diagnose (troubleshoot) incorrect operation of motor-driven accessory circuits, determine necessary action, and pass a written test covering the task with 100% accuracy.
Inform students that this Lesson will cover the Diagnosis of Motor-Driven Accessory Units, primarily Power Window Motors, Power Seats, Power Mirrors and Blower Motors.
POWER WINDOWS: Instruct students that a power window uses a small DC motor to move the window glass up and down. The major parts of a power window system include: 1. WINDOW SWITCH (spring-loaded, normally-off switch that controls current flow to window motors). 2. WINDOW MOTOR (reversible electric motor that drives gearbox). 3. WINDOW MOTOR GEARBOX (gear mechanism mounted on window motor for increasing torque applied to window regulator gear). 4. WINDOW REGULATOR (gear and lever mechanism for sliding window up and down in its track). 5. WINDOW MOTOR HARNESS (wiring that connects switches to window motors). 6. BREAKER POINTS (small points in window motors that protect motor from damage if switch is held too long after full glass travel).
Teach students that the window switches are normally fed current whenever the ignition switch is on. A fuse or circuit breaker protects the power window circuit from shorts and excess current draw. Inform students that when the driver presses a window switch, current flows to one of the window motors. The motor armature spins a worm gear. The worm gear then acts on a larger gear in the motor gearbox. A small output gear transfers this high torque to a large toothed gear or track on the window regulator. If the window switch is pushed the other way, Current flow through the window motor is reversed. This causes the armature to spin the other way and the window moves in the opposite direction.
Troubleshooting Power Windows: Instruct students that before troubleshooting a power window problem check for proper operation of all power windows. If one of the control wires that run from the independent switch to the master switch is cut (open), the power window may operate in just one direction. The window may go down but not up, or vice versa. However, if one of the direction wires that run from the independent switch to the motor is cut (open), the window will not operate in either direction. Inform students that the direction wires and the motor must be electrically connected to permit operation and change of direction of the electric lift motor in the door.
Tell students to check out the following information when dealing with Power Windows. 1. If both rear-door windows fail to operate from the independent switches, check the operation of the window lockout (if the vehicle is so equipped) and the master control switch. 2. If one window can move in one direction only, check for continuity in the control wires (wires between the independent control switch and the master control switch). 3. If all windows fail to work or fail to work occasionally, check, clean, and tighten the ground wire(s) located either behind the driver's interior door panel or under the dash on the driver's side. A defective fuse or circuit breaker could also cause all the windows to fail to operate. 4. If one window fails to operate in both directions, the problem could be a defective window lift motor. The window could be stuck in the track of the door, which could cause the circuit breaker built into the motor to open the circuit to protect the wiring, switches, and motor from damage. To check for a stuck door glass, attempt to move (even slightly) the door glass up and down, forward and back, and side to side. If the window glass can move slightly in all directions, the power window motor should be able to at least move the glass. 5. Slower-than-normal operating speeds are an indication of excessive resistance or of binding in the mechanical linkage. Use the voltage drop test method to locate the cause of excessive resistance. Excessive resistance can be in the switch circuits, the ground circuit, or in the motor. If the problem is mechanical, lubricate the track and check for binding or bent linkage.
SAFETY WARNING: Follow the manufacturer's recommended procedure when removing the power window motor. The springs used in window regulators can cause serious injury if removed improperly.
POWER SEATS: Instruct students that a power seat uses small electric motors to drive a seat transmission that repositions the seat on its track. The major parts of a power seat system are: 1. POWER SEAT SWITCHES (switches on seat or door panel that control current flow to seat motors). 2. SEAT MOTORS (small, reversible DC motors that provide power to move seats into different positions). 3. SEAT DRIVE CABLES (steel cables that transfer motion from seat motors to seat transmission). 4. SEAT TRANSMISSION (gearbox that changes rotating motion from motors and cables into linear motion for the seats). 5 . SEAT TRACK (metal guides that allow seat to move on the base of the floor mount assembly). Several switches are normally provided to operate the power seat motors. One may provide for back and forth movement on the tracks by energizing the correct motor. Another switch can raise and lower the seat by energizing a different motor. Another switch or another position in a multi-position switch can energize a seat tilting motor.
Instruct students that the power seat system is usually very simple to troubleshoot. Have students test for voltage to the input of the switch control. If voltage is available to the switch, tell students to remove it from the seat or arm rest. Using a continuity chart from the service manual, instruct students to test the switch for proper operation. If the switch is operating properly, let students know it may be necessary to remove the seat to test the motors and circuits to the motors. The power seat motors are tested in the same manner as the power window motor. Be sure to inform students to test each armature of the trimotor. Let them know that if any of the armatures fail to operate, the trimotor must be replaced as a unit.
SAFETY WARNING: Be careful when making the jumper wire connection to test the motor. Instruct students to not place their hands in locations where they can become pinched or trapped when the seat moves.
Inform students that noisy operation of the seat can generate from the motor, transmission, or cable. If the motor or transmission is the cause of the noise, let students know it must be replaced. Tell students that a noisy cable can usually be cured with a dry lubricant, provided the cable is not damaged.
POWER MIRRORS: Instruct students that power mirrors use tiny electric motors to pivot the rear view mirrors. A multi-position switch activates the small motors inside the mirrors. The basic parts of a power rear view mirror system include: 1. MIRROR SWITCH (multi-position switch that can send current to both mirror motors and reverse current flow through motors). 2. VERTICAL CONTROL MOTOR (small, reversible, DC motor that actuates up and down swivel of rear view mirror glass). 3. HORIZONTAL CONTROL MOTOR (small, reversible, DC motor that actuates side to side swivel of mirror glass). 4. GEAR REDUCTION (small gear and screw mechanisms that increase output torque and convert motor rotation into linear action). 5. MIRROR (reflective coated glass that is attached to swivel base and to output plungers of mirror motors). 6. MIRROR HOUSING (metal or plastic housing that encloses parts of rear view mirror). 7. POWER MIRROR HARNESS (wiring that connects switch to mirror motors). The power mirror switch is usually a "joy stick" or four-position type switch. It can be moved up and down and from side to side. The contacts in the switch connect and disconnect to control current flow to the mirror motors to correspond to switch movement.
Teach students that basic testing methods can be used to troubleshoot a power mirror system. If neither mirror works, tell students to check the fuse and power supply circuit. If only one mirror fails to adjust, check its switch and motors. Usually, students will have to remove the door panel to test the switch, wiring, and motors. Inform students that a heat gun is often used to warm and remove the rear view mirror glass if cracked or if the motors can be replaced. Many manufacturers recommend replacement of the whole power mirror assembly if anything is wrong with it.
BLOWER MOTORS: Instruct students that the same blower motor moves air inside the vehicle for air conditioning, heat, and defrosting or defogging. The fan switch controls the path that the current follows to the blower motor. The motor is usually a permanent-magnet, one-speed motor that operates at its maximum speed with full battery voltage. The switch gets current from the fuse panel with the ignition switch on, and then directs full battery voltage to the blower motor for high speed and to the blower motor through resistors for lower speeds. See Teach students that conventional blower motor speed is controlled by sending current through a resistor block. The resistor block is a series of resistors with different values. There is usually one less resistor than there are fan speed positions because the high-speed circuit bypasses the resistors. The higher the resistance value, the slower the fan speed. The position of the switch determines which resistor will be added to the circuit. Inform students that if the customer complaint is that the fan operates in only a couple of speed positions, the most likely cause is an open resistor in the resistor block.
SAFETY PRECAUTION: The resistor block is mounted in the heater/air conditioning housing where it is cooled by air flow from the fan. Tell students to not run the fan motor with the resistor block removed from the air flow because it may overheat and burn the coils.
Teach students that if the blower motor does not operate at any speed, the problem could be any of the following: 1. A defective ground wire or ground wire connection 2. A defective blower motor (not repairable; must be replaced) 3. An open circuit in the power-side circuit, including fuse, wiring, or fan switch
If the blower works on lower speeds but not on high speed, inform students that the problem is usually an inline fuse or high speed relay that controls the heavy current flow for high-speed operation. The high-speed fuse or relay usually fails as a result of internal blower motor bushing wear, which causes excessive resistance to motor rotation. At slow blower speeds, the resistance is not as noticeable and the blower operates normally. Let students know that the blower motor is a sealed unit, and if defective, must be replaced as a unit. 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.
The blower motor can be tested using a clamp-on DC ammeter. Inform students that most blower motors do not draw more than 15 A on high speed. A worn or defective motor usually draws more current than normal and could damage the blower motor resistors or blow a fuse if not replaced.
Let students know that constantly running blower motors are more common in ground side switch systems. A short to ground at any point on the ground side of the circuit will cause the motor to run. Other areas to check include the switch and the circuit between the switch and the resistor block.
In insulated side switch circuits (Battery Positive Side), check for copper-to-copper shorts in the power side of the system. If the motor is receiving power from another circuit, due to a copper-to-copper short, the motor will continue to run whenever current is flowing through that circuit. Some systems may incorporate a relay, and if the contact points fuse together, the motor will continue to operate.
Objective 1. / Formative assessment / Instructor will observe students as they practice the procedure to assure correct procedure and safety practices are being followed. A checklist will be utilized to chart student progress on the task. Questioning techniques will be utilized as necessary to demonstrate student comprehension / Adaptations and/or accommodations for special needs students will be added if required.
STUDENT ASSESSMENT: (Assess student progress with performance criteria.)
Objective 1 / Summative assessment / written test questions on stated objective / adaptation and / or accommodations for special needs students will be added if required
IMPACT--Reflection/Analysis of Teaching and Learning: (How did students’ progress in relation to the state objectives? Was the instruction successful? Analyze samples of student work particularly that which is unsatisfactory, for the purpose of planning further instruction.)
REFINEMENT--Lesson Extension and Follow-up: (To be filled in as the lesson is modified during initial planning and/or during the teaching learning process.)