Automotive Service Technology Section C/Automotive Special Problems
Course HS Title:
Automobile Service Technology/Special Problems
Program:
KCTCS Courses included in HS Title: (Lesson is prepared for course highlighted.)
KCTCS Course No.
KCTCS Course Title
Introduction/Context
This lesson will instruct the student on how to diagnose (troubleshoot) incorrect operation of cruise control systems, 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.
Prepared By
School
Date:
Grade Level
No. Students
No.IEP's:
Lesson Length:
Task
Diagnose (troubleshoot) incorrect operation of cruise control systems; determine necessary action.
No.
Objective
1
Given the proper tools and instruction, the student will be able to diagnose (troubleshoot) incorrect operation of cruise control systems, determine necessary action, and pass a written test covering the task with 100% accuracy.
Instruct students that cruise (speed) control is a combination of electrical and mechanical components designed to maintain a constant, set vehicle speed without driver pressure on the accelerator pedal. Major components of a typical cruise control system include the following: 1. Servo unit. The servo unit attaches to the throttle linkage through a cable or chain. The servo unit controls the movement of the throttle by receiving a controlled amount of vacuum from a control module. Some systems use a stepper motor and do not use engine vacuum. 2. Computer or cruise control module. This unit receives inputs from the brake switch, throttle position (TP) sensor, and vehicle speed sensor. It operates the solenoids or stepper motor to maintain the set speed. 3. Speed set control. A speed set control is a switch or control located on the steering column, steering wheel, dash, or console. Many cruise control units feature coast, accelerate, and resume functions. 4. Safety release switches. Whenever the brake pedal is depressed, the cruise control system is disengaged through use of an electrical and vacuum switch, usually located on the brake pedal bracket. Both electrical and vacuum releases are used to be certain that the cruise control system is released, even in the event of failure of one of the release switches.
Inform students that a typical cruise control system can be set only if the vehicle speed is 30 mph (minimum engagement speed) or more. In a non-computer-operated system, the transducer contains a low-speed electrical switch that closes whenever the speed-sensing section of the transducer (the electrical and speed sensing control unit) senses a speed exceeding the minimum engagement speed.
Instruct students that when the set button is depressed on the cruise control, solenoid values on the servo unit allow engine vacuum to be applied to one side of the diaphragm, which is attached to the throttle plate of the engine through a cable or linkage. Teach students that the servo unit usually contains two solenoids to control the opening and closing of the throttle. One solenoid opens and closes to control the passage, which allows engine vacuum to be applied to the diaphragm of the servo unit, increasing the throttle opening. Another solenoid is used to bleed air back into the sensor chamber to reduce the throttle opening. The throttle position (TP) sensor or a position sensor, inside the servo unit, sends the throttle position information to the cruise control module.
NONCOMPUTER-CONTROLLED RESUME-TYPE CRUISE CONTROL: Instruct students that most resume-style non computer-controlled cruise control systems use a two-piece rubber clutch to retain a "mechanical memory" of the vehicle road speed. Let students know that depressing the brake pedal causes a vacuum-release solenoid to release vacuum from the servo unit, and the cruise control stops maintaining vehicle speed. When "resume" on the switch is pushed, the vacuum solenoid closes and vacuum is again applied to the servo unit. The speed is "remembered" by the position of the split rubber clutch. This type of cruise control is not seen very often in today’s Auto Shops.
COMPUTER-CONTROLLED/ELECTRONIC CRUISE CONTROL: Inform students that most computer-controlled cruise control systems use the vehicle's speed sensor input to the engine-control computer for speed reference. Let students know that computer-controlled cruise control units can also use servo units for throttle control, control switches for driver control of cruise control functions, and both electrical and vacuum brake pedal release switches. Instruct students that the vehicle computer for electronic cruise control analyzes and acts on inputs of vehicle speed and engine load. Let students know that most of today's vehicles use a stepper motor that pulls on a strap to move the throttle. Many vehicles use "drive by wire," in which the throttle is controlled by a computer. These vehicles are basically on fulltime cruise control, which is continuously selected by throttle position as the driver moves the gas pedal. Inform students that electronic cruise control inputs include a vehicle speed sensor to sense vehicle speed and switches to release the clutch and/or brake.
INTELLIGENT/ADAPTIVE CRUISE CONTROL: Instruct students that some newer vehicles have an optional intelligent cruise control, also called adaptive cruise control, which will maintain a selected distance from the vehicle ahead dependent on its speed. A radar or infrared sensor in the grille of the vehicle detects objects in front and sends a signal to a module. The computer can detect a vehicle at up to 390 feet (120 meters) determine its speed, and then apply either the brakes or accelerator to maintain the designed distance. Typical distance settings at 60 mph are 195 feet, 130 feet, and 90 feet. Let students know that the brakes can apply at 25% braking power, which is a substantial amount of braking. When the road ahead is clear, the system accelerates once again to the preset speed. During slowing, the system illuminates the brake lights. Inform students that a driver has the option of using either the intelligent system or conventional cruise control. Instruct students that the distance sensor has a narrow range of operation so it does not see oncoming vehicles on narrow roads. However, system performance can be poor on winding roads. Let students know that the sensor can only sense hard objects like a motorcycle but cannot detect soft objects like animals or humans. Make students aware that the system disengages during wet weather to prevent contamination of the sensor and confusion of the computer.
TROUBLESHOOTING CRUISE CONTROL: Instruct students that cruise control system troubleshooting is usually performed using the step-by-step procedure as specified by the vehicle manufacturer. The usual steps in the diagnosis of an inoperative or incorrectly operating cruise control include the following: Step 1 Check that the cruise control fuse is not blown and that the cruise control dash light is on when the cruise control is turned on. Step 2 Check for proper operation of the brake and/or clutch switch. Step 3 Inspect the throttle cable and linkage between the sensor unit and the throttle plate for proper operation without binding or sticking. Step 4 Check the vacuum hoses for cracks or other faults. Step 5 Use a hand-operated vacuum pump and check that the vacuum servo unit can hold vacuum without leaking. Step 6 Check the servo solenoids for proper operation, including a resistance measurement check. A quick method used by many dealers is to use known-good components that can be quickly plugged in to check for proper operation. Always check the brake lights to see that they operate. The brake on and off switch is an essential part of cruise control, and if the brake lights do not work, cruise control cannot operate. Computer-controlled/Electronic cruise control diagnosis begins with a look at the service information. This is followed by testing with a scan tool to find defective sensors and switches or to locate a problem in an electrical circuit.
Applications/Practice
1
Refer to content
Evaluation and feedback Prior to Testing or Lab Work
1
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.)
1
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.)
