Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Starting System
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Starting System
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Subject: Auto Mechanical Works
Class: Senior Secondary 2
Term: 3rd Term
Week: 2
Theme: Safety And Maintenance
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This topic covers the essential principles of diagnosing and rectifying common faults within a vehicle's starting system. A reliable starting system is fundamental to vehicle operation, particularly in Nigeria where vehicles are crucial for transportation, commerce, and public services (e.g., commercial buses, taxis, delivery vans, agricultural machinery). Understanding how to troubleshoot and repair starting faults is a critical skill for aspiring auto mechanics, enabling them to provide valuable services and contribute to the efficiency of the transport sector.
engagement with the flywheel through an inspection hole.
Rectification: Replace or rebuild the starter motor, focusing on the Bendix drive mechanism. In rare cases of severe flywheel damage, the flywheel may need replacement.
Fault Type 5: Starter Stays Engaged / Runs On Symptoms: After the engine starts, the starter motor continues to spin or makes a grinding noise.
Possible Causes: Faulty starter solenoid (sticking in the engaged position). Faulty ignition switch (failing to return to "ON" or "ACC" position). Damaged starter motor Bendix drive not retracting.
Diagnostic Steps:
1. Release Ignition Key: Ensure the ignition key returns to the "ON" position freely after starting. If it sticks, the switch is faulty.
2. Listen to Solenoid: A continuous click/hum from the solenoid after the engine starts indicates it's staying engaged.
Rectification: Replace faulty ignition switch. Replace faulty starter solenoid (or the entire starter motor if integrated). Replace or rebuild the starter motor if the Bendix drive is at fault. Safety Precautions for Starting System Diagnostics: Always disconnect the negative battery terminal before working on the starting system, especially when removing or installing components. Ensure the vehicle is in Park (automatic) or Neutral (manual) with the parking brake engaged before testing the starter. Wear appropriate personal protective equipment (PPE) such as safety glasses. Be cautious of hot engine components and rotating parts. Avoid shorting electrical terminals, as this can cause sparks, battery explosions, or damage to electrical components. but the engine does not crank. Dash lights may dim significantly during the click.
Possible Causes: Severely discharged battery, but enough power to energise the solenoid. Loose or corroded battery cables, particularly the main positive or negative cable to the starter motor or engine block. Faulty starter solenoid (unable to pass high current to the motor). Faulty starter motor (internal short, seized bushings/bearings). Engine mechanical issue (rare, but a seized engine can prevent cranking).
Diagnostic Steps:
1. Check Battery State: As with "No Crank, No Click." A weak battery might energise the solenoid but not have enough current for the motor.
2. Check Battery Cables and Connections: Visually inspect the large battery cables (positive to starter, negative to engine block/chassis) for corrosion, looseness, or damage. Pay close attention to the termination points. Perform a voltage drop test across the cables while attempting to start. Excessive voltage drop indicates high resistance.
3. Tap the Starter Motor (Temporary Fix/Diagnostic): With the key held in the "START" position, gently tap the starter motor casing with a hammer or wrench. If it then cranks, it suggests worn brushes or sticky commutator in the starter motor. This is a diagnostic, not a permanent repair.
4. Check Solenoid and Motor Current Draw: This requires an ammeter clamp, typically found in professional workshops. High current draw with no crank indicates a shorted starter motor. Low current draw indicates a poor connection or faulty solenoid.
Rectification: Clean and tighten battery cables and terminals. Charge or replace battery. Replace faulty starter solenoid (often integrated with the starter motor). Replace or rebuild the starter motor if it has worn brushes or seized parts.
Fault Type 3: Slow Crank / Weak Crank Symptoms: Engine cranks slowly and struggles to turn over. It may eventually start, or it may just make a groaning sound and fail to start.
Possible Causes: Partially discharged or weak battery. Excessive resistance in battery cables or connections (corrosion, loose terminals). Worn starter motor components (brushes, bushings, armature). Incorrect engine oil viscosity (too thick for cold weather, less common in Nigeria). Engine mechanical drag (e.g., worn bearings, internal friction).
Diagnostic Steps:
1. Check Battery State and Load Test: Test battery voltage. Perform a battery load test (if equipment is available) to assess its cranking ability. A battery might show good voltage but fail under load.
2. Voltage Drop Test: Perform voltage drop tests across the positive and negative battery cables while cranking. A drop exceeding 0.5V on the positive cable or 0.2V on the negative cable indicates excessive resistance.
3. Check Starter Motor Condition: Listen to the sound of the starter. A slow, struggling sound without excessive current draw suggests internal wear.
Rectification: Charge or replace the battery. Clean, tighten, or replace corroded/damaged battery cables and terminals. Replace or rebuild the starter motor.
Fault Type 4: Starter Spins, Engine Does Not Crank Symptoms: The starter motor makes a whirring sound, indicating it is spinning, but the engine itself does not turn over.
Possible Causes: Faulty starter motor pinion gear (Bendix drive) or overrunning clutch. The pinion gear is not extending to engage the flywheel, or it's extending but slipping. Damaged flywheel ring gear teeth (less common, but possible).
Diagnostic Steps:
1. Listen Carefully: Determine if the spinning sound is consistent with the starter motor spinning freely, indicating lack of engagement.
2. Visual Inspection (If Accessible): If possible, visually inspect the starter motor's pinion gear engagement with the flywheel through an inspection hole.
Rectification: Replace or rebuild the starter motor, focusing on the Bendix drive mechanism. In rare cases of severe flywheel damage, the flywheel may need replacement.
Fault Type 5: Starter Stays Engaged / Runs On Symptoms: After the engine starts, the starter motor continues to spin or makes a grinding noise.
Possible Causes: Faulty starter solenoid (sticking in the engaged position). Faulty ignition switch (failing to return to "ON" or "ACC" position). Damaged starter motor Bendix drive The starting system is responsible for cranking the engine to initiate combustion. It typically consists of the battery, ignition switch, starter solenoid, starter motor, and associated wiring. This section details common starting faults and systematic diagnostic procedures. 2.1 Common Starting System Faults and Their Manifestations: The primary faults can be categorised based on how the engine reacts when the ignition key is turned to the "START" position:
1. No Crank, No Click: When the ignition key is turned, absolutely nothing happens. No sound from the starter motor, no clicking sound from the solenoid.
2. No Crank, Single Click: A distinct "click" is heard, usually from the starter solenoid, but the engine does not crank.
3. Slow Crank / Weak Crank: The engine cranks, but very slowly or weakly, struggling to turn over. It may sound like a sluggish groan rather than a rapid spin.
4. Starter Spins, Engine Does Not Crank: The starter motor can be heard spinning freely, but it does not engage with the engine flywheel, and thus the engine does not turn over.
5. Starter Stays Engaged / Runs On: After the engine starts, the starter motor continues to spin or make a grinding noise, failing to disengage from the flywheel. 2.2 Systematic Procedures for Locating and Rectifying Starting Faults: This section outlines the diagnostic steps and potential rectifications for each common fault.
Fault Type 1: No Crank, No Click Symptoms: Ignition key turned, no response from starter system. Dash lights may or may not come on.
Possible Causes: Dead or severely discharged battery. Loose, corroded, or disconnected battery terminals. Faulty ignition switch. Open circuit in starter control wiring (e.g., blown fuse, broken wire, faulty relay). Faulty starter motor solenoid (electrical circuit issue, not mechanical). Faulty starter motor (internal electrical fault). Security system/immobiliser activation (less common for simple faults, but possible).
Diagnostic Steps:
1. Check Battery: Visually inspect battery terminals for corrosion, looseness. Clean and tighten as necessary. Check battery voltage with a multimeter. A healthy battery should read 12.6V or higher. Below 12V indicates discharge. Attempt to jump start the vehicle. If it starts with a jump, the battery is dead or weak, or the charging system is faulty.
2. Check Fuses and Relays: Locate the fuse box (under dashboard or in engine bay). Identify and check the starter fuse/relay. A blown fuse will have a broken filament. Swap relays with a known good one if unsure.
3. Check Ignition Switch: With a multimeter, check for voltage at the starter solenoid "S" terminal (small wire) when the ignition key is turned to the "START" position. If no voltage, the issue is likely the ignition switch or its associated wiring.
4. Check Starter Motor and Solenoid: Bypass Test (Caution: Only for experienced personnel and short duration): With the transmission in Neutral/Park and parking brake engaged, briefly jump the two large terminals on the starter solenoid (or jump from the battery positive to the small "S" terminal on the solenoid). If the starter motor cranks, the starter motor and solenoid are likely good, indicating a problem upstream (wiring, ignition switch, relay). This test should only be performed by a qualified individual to avoid damage or injury.
Rectification: Clean and tighten battery terminals. Charge or replace the battery. Replace blown fuses or faulty relays. Replace faulty ignition switch. Repair/replace faulty wiring. Replace faulty starter motor or solenoid.
Fault Type 2: No Crank, Single Click Symptoms: A single, distinct click is heard from the starter solenoid, but the engine does not crank. Dash lights may dim significantly during the click.
Possible Causes: Severely discharged battery, but enough power to energise the solenoid. Loose or corroded battery cables, particularly the main positive or negative cable to the starter motor or engine block. Faulty starter solenoid (unable to pass high current to the motor). Faulty starter motor (internal short, seized bushings/bearings). Engine mechanical issue (rare, but a seized engine can prevent cranking). * Diagnostic Steps:
1. Check Battery State: As with "No Crank, No Teacher Activities: Introduction (10 minutes): Initiate a brief discussion on the importance of a functional starting system for vehicles in everyday Nigerian life (e.g., danfo buses, commercial motorcycles, private cars). Recap the basic components of the starting system (battery, ignition switch, starter motor, solenoid, cables). Use diagrams or actual components if available. Introduce the performance objectives for the lesson: locating and rectifying simple starting faults.
Explanation of Common Faults (20 minutes): Present each common starting fault type (No Crank/No Click, No Crank/Single Click, Slow Crank, Starter Spins, Starter Stays Engaged) using a projector, chalkboard, or chart. For each fault, describe its symptoms and discuss the most probable causes. Use real-world examples relevant to Nigerian vehicle types and common issues encountered by local mechanics. Demonstration of Diagnostic Procedures (30 minutes): Practical Demonstration (Preferred): If a non-starting vehicle or a dismantled starting system (battery, starter motor, solenoid) is available in the workshop, demonstrate the diagnostic steps for one or two common faults (e.g., checking battery voltage, inspecting terminals, bypassing the solenoid for a brief test). If a live vehicle is used, ensure all safety precautions are strictly followed.* Simulated Demonstration (Alternative): If practical demonstration is not feasible, use detailed diagrams, flowcharts, and verbal explanations to illustrate each diagnostic step. Role-play scenarios with students to simulate fault finding. Emphasise the use of multimeter for voltage checks and continuity tests. Explain the importance of systematic troubleshooting rather than guessing.
Rectification Techniques (15 minutes): For each fault type, explain the appropriate rectification steps (e.g., cleaning terminals, charging/replacing battery, replacing fuses/relays, replacing/rebuilding starter motor/solenoid). Show relevant tools (terminal cleaner, wrenches, multimeter).
Safety Precautions (5 minutes): Reinforce all safety measures (disconnecting battery, neutral/park, PPE, avoiding shorts) critically throughout the demonstration.
Student Activities: Active Listening and Note-taking (Ongoing): Students will actively listen to explanations, observe demonstrations, and take comprehensive notes.
Question and Answer Session (10 minutes): Students will ask questions for clarification during and after explanations/demonstrations.
Scenario Analysis (15 minutes): The teacher presents specific starting fault scenarios (e.g., "A commercial bus driver reports that his vehicle just clicks once and doesn't crank. What are the likely causes and how would you start diagnosing it?"). Students discuss in small groups and propose diagnostic and rectification steps. Practical Observation/Simulation (Ongoing): Students will observe the teacher's practical demonstration keenly. If components are available, they will be encouraged to handle and identify parts and trace wiring connections.
Tool Identification: Students identify and name tools used in diagnosing and rectifying starting system faults.
Safety Procedure Recitation: Students will be asked to list key safety procedures before practical engagement.
Roadside Assistance and Entrepreneurship: The ability to diagnose and rectify starting faults is a core skill for roadside assistance providers and independent mechanics in Nigeria. Students can learn to troubleshoot common issues like dead batteries or faulty solenoids, which frequently occur on busy roads or in remote areas, leading to immediate earning opportunities. This knowledge can also be integrated with local transport networks (e.g., Okada riders, danfo drivers) where quick repairs mean minimal downtime and lost income.
Vehicle Fleet Management: For businesses operating vehicle fleets (e.g., logistics companies, taxi services, government agencies with official cars), understanding starting system diagnostics allows for faster identification of issues, preventive maintenance, and reduced operational costs by minimising vehicle downtime. Students could potentially work as in-house mechanics for such organisations, ensuring their vehicles are always ready for service. Personal Vehicle Maintenance and Cost Savings: Vehicle owners in Nigeria often face high repair costs. Knowing how to perform basic starting system checks can help individuals diagnose problems themselves, saving money on unnecessary mechanic visits or parts, and preventing being overcharged for simple repairs. This empowers individuals to better maintain their own or family vehicles.