Repairs of water temperature guage, oil pressure guage, horn, relay, wiper, switch, screen washer pump, break ,indicator, door switch
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Subject: Auto Electrical Works
Class: Senior Secondary 2
Term: 3rd Term
Week: 3
Theme: Auxiliary System
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Identify the problems with any faultyauxiliary unit. Repair, wherepossible and necessary, the malfunctioningauxiliary unit.
with pressure.
4. Circuit Continuity: Check continuity of wires between sending unit and gauge.
Repair Procedures:
1. Address Low Oil Pressure: If the mechanical gauge confirms low pressure, advise on checking oil level, oil filter, or deeper engine diagnostics (e.g., oil pump, bearings).
2. Replace Sending Unit: If electrical tests confirm the sending unit is faulty.
3. Repair Wiring: Fix loose connections, corrosion, or broken wires.
4. Replace Gauge: If the dashboard gauge is faulty.
C. Horn Function: Provides an audible warning signal.
Common Faults:
1. Horn not working at all: Most common. Can be a faulty horn switch, faulty horn relay, broken fuse, open circuit in wiring, or a faulty horn unit itself.
2. Horn sounds weak/intermittent: Often a poor connection, corroded terminals, or a weak horn unit.
3. Horn stuck on: Faulty horn switch (stuck closed) or a stuck horn relay.
Diagnostic Steps:
1. Check Fuse: Locate and inspect the horn fuse in the fuse box. Replace if blown.
2. Horn Button/Switch Test: Use a multimeter to check for continuity across the horn switch terminals when pressed. If no continuity, switch is faulty.
3. Relay Test: Locate the horn relay. Listen for a click when the horn button is pressed (ignition on). No click suggests a faulty relay or no power to the coil. Swap the horn relay with a known good, identical relay from another circuit (e.g., fan relay) if available.
Test the relay terminals: identify power in, switch out, coil power, and coil ground. Check for 12V supply and continuity when coil is energized.
4. Horn Unit Test: Disconnect the horn unit and apply direct 12V from the battery (with a fused jumper wire). If it doesn't sound, the horn unit is faulty.
5. Wiring Check: Trace wiring from fuse to relay, relay to horn, and horn to ground for continuity and shorts.
Repair Procedures:
1. Replace Blown Fuse: Always identify the cause of the blown fuse before replacing.
2. Repair/Replace Horn Switch: Clean contacts or replace the switch.
3. Replace Horn Relay: If diagnosed faulty.
4. Replace Horn Unit: If it fails the direct power test.
5. Repair Wiring/Connections: Clean corroded terminals, tighten loose connections, repair broken wires.
D. Relay Function: An electromagnetic switch that allows a small current to control a larger current. Used in high-current circuits like horns, headlamps, fuel pumps, etc., to protect switches and wiring.
Common Faults:
1. Relay not clicking/not activating: No power to the coil, faulty coil, or faulty ground.
2. Relay clicks but no power to component: Burnt contacts inside the relay, open circuit on the power side.
3. Relay stuck "on": Contacts fused together inside the relay.
Diagnostic Steps: (General for a 4-pin or 5-pin automotive relay)
1. Listen for Click: With ignition on, activate the circuit controlled by the relay (e.g., press horn button). A distinct click should be heard.
2. Power & Ground to Coil: Identify coil terminals (often 85 and 86). Check for 12V across these terminals when the circuit is activated.
3. Power to Load Terminals: Identify load terminals (often 30 and 87/87a). Check for 12V at terminal 30 (constant power from fuse) and then at terminal 87 when the relay is activated.
4. Continuity Check (bench test): Use a multimeter to check continuity across terminals 30 and 87 (normally open) or 30 and 87a (normally closed) when 12V is applied to the coil.
5. Swap with Known Good Relay: The quickest diagnostic if an identical relay is available.
Repair Procedures: Relays are typically sealed units and are replaced, not repaired.
E. Wiper System (Motor, Linkage, Blades)
Function: Clears rain, dust, and debris from the windscreen. Components include the motor, linkage arms, wiper blades, and a control switch.
Common Faults:
1. Wipers not working at all: Blown fuse, faulty wiper motor, faulty wiper switch, open circuit.
2. Wipers move slowly: Weak motor, stiff linkage, low voltage, or worn bushings.
3. Wipers stop mid-sweep: Faulty park mechanism in the motor, stiff linkage, intermittent motor fault.
4. Wipers operate at one speed only: Faulty wiper switch or faulty motor internal speed control.
5. This section provides a detailed breakdown of the function, common faults, diagnostic steps, and repair procedures for each auxiliary unit.
A. Water Temperature Gauge Function: Indicates the operating temperature of the engine coolant. A typical system consists of a sending unit (thermistor) in the engine block and a gauge on the dashboard.
Common Faults:
1. Gauge reads consistently high/overheating: Often indicates actual engine overheating (low coolant, faulty thermostat, radiator issues) or a faulty sending unit/gauge circuit.
2. Gauge reads consistently low/cold: May indicate a faulty sending unit, faulty thermostat (stuck open), or an open circuit in the gauge wiring.
3. Gauge reads zero/no movement: Usually an open circuit, faulty sending unit, or faulty gauge itself.
4. Gauge reads maximum/pegged hot: Often a short circuit in the sending unit wire or a faulty sending unit/gauge.
Diagnostic Steps:
1. Visual Inspection: Check coolant level, wiring connections to the sending unit and gauge for looseness or corrosion.
2. Sending Unit Test: Disconnect the wire from the sending unit. If the gauge drops to cold, the wiring/gauge is likely okay, and the sending unit is faulty or the engine is genuinely cold. Ground the disconnected wire (momentarily). If the gauge pegs to hot, the wiring/gauge is okay, and the sending unit is faulty.
Caution: Do not ground for too long to avoid gauge damage. Measure the resistance of the sending unit with a multimeter while the engine warms up. Resistance should decrease as temperature increases. Compare to manufacturer specifications.
3. Gauge Test: Apply a known resistance value to the gauge input (simulating the sending unit) using a resistor box or variable resistor. The gauge should respond accordingly.
4. Circuit Continuity: Check continuity of wires between sending unit and gauge using a multimeter.
Repair Procedures:
1. Replace Sending Unit: If testing confirms the sending unit is faulty.
2. Repair Wiring: Fix loose connections, corroded terminals, or broken wires.
3. Replace Gauge: If the gauge itself is faulty and cannot be repaired.
4. Address Engine Overheating: If the gauge accurately reports a high temperature, the underlying engine issue (e.g., low coolant, faulty fan, blocked radiator) must be addressed.
B. Oil Pressure Gauge Function: Indicates the lubricating oil pressure within the engine. Similar to the temperature gauge, it uses a sending unit and a dashboard gauge.
Common Faults:
1. Gauge reads low/zero: Could be genuinely low oil pressure (low oil level, worn engine bearings, faulty oil pump) or a faulty sending unit/circuit.
2. Gauge reads high: Less common, but could indicate a faulty sending unit or a blockage in the oil galleries.
3. Gauge reads maximum/pegged high: Often a short circuit in the sending unit wire or a faulty sending unit/gauge.
4. Gauge reads minimum/zero: Often an open circuit, faulty sending unit, or faulty gauge itself.
Diagnostic Steps:
1. Visual Inspection: Check engine oil level. Check wiring to the sending unit and gauge.
2. Mechanical Gauge Test: Crucial step. Install a known good mechanical oil pressure gauge directly into the engine's oil gallery (where the sending unit screws in). Compare this reading to the dashboard gauge. This determines if the issue is actual low oil pressure or an electrical fault.
3. Sending Unit Test: Disconnect the wire from the sending unit. If the gauge drops to zero, the wiring/gauge is likely okay, and the sending unit is faulty or oil pressure is genuinely low. Ground the disconnected wire (momentarily). If the gauge pegs to max, the wiring/gauge is okay, and the sending unit is faulty. Measure resistance of the sending unit. Resistance typically changes with pressure.
4. Circuit Continuity: Check continuity of wires between sending unit and gauge.
Repair Procedures:
1. Address Low Oil Pressure: If the mechanical gauge confirms low pressure, advise on checking oil level, oil filter, or deeper engine diagnostics (e.g., oil pump, bearings).
2. Replace Sending Unit: If electrical tests confirm the sending unit is faulty.
3. Repair Wiring: Fix loose connections, corrosion, or broken wires.
4. Replace Gauge: If the dashboard gauge is faulty.
C. Horn Function: Provides an audible warning signal.
Common Faults: 1. *Horn not working for dome lights, door ajar warnings, security systems.
Common Faults:
1. Dome light stays on/doesn't come on: Faulty switch (stuck open/closed), wiring issue, faulty bulb.
2. Door ajar warning on/off incorrectly: Faulty switch.
3. Security system malfunction related to door: Faulty switch.
Diagnostic Steps:
1. Visual Inspection: Locate the door switch (often a plunger type in the door jamb or a rotary type within the latch mechanism). Check for physical damage or sticking.
2. Continuity Test: Disconnect the switch. Check continuity across the terminals. For a typical plunger switch, there should be continuity when the plunger is out (door open) and no continuity when pressed in (door closed), or vice versa depending on its design (normally open/normally closed).
3. Power/Ground Check: Check for power or ground at the switch connector depending on its circuit design (e.g., dome light circuit often grounds through the door switch). * Repair Procedures:
1. Clean/Lubricate Switch: Sometimes sticky plungers can be freed.
2. Adjust Switch: If it's a screw-in type and its position is adjustable.
3. Replace Door Switch: If diagnosed faulty.
4. Repair Wiring: Fix loose connections or broken wires. ground are present but no sound, the pump motor is faulty.
4. Bench Test Pump: If removed, apply direct 12V to the pump terminals to see if it operates.
5. Nozzle/Hose Inspection: Visually inspect nozzles for blockages (use a thin needle to clear). Check hoses for kinks, leaks, or disconnections.
Repair Procedures:
1. Refill Reservoir.
2. Replace Fuse.
3. Replace Washer Pump: If the motor is faulty.
4. Clear Nozzles: Use a pin or compressed air.
5. Repair/Replace Hoses: Fix kinks, reconnect detached hoses, seal leaks.
6. Replace Washer Switch: If diagnosed faulty.
H. Brake Light Switch Function: Activates the brake lights when the brake pedal is pressed.
Common Faults:
1. Brake lights not working: Most common. Faulty switch, blown fuse, faulty bulbs, open circuit.
2. Brake lights stuck on: Faulty switch (stuck closed) or improperly adjusted switch.
3. Intermittent brake lights: Loose connection, worn switch.
Diagnostic Steps:
1. Check Bulbs & Fuse: Inspect brake light bulbs and the brake light fuse.
2. Switch Position & Adjustment: Observe the switch's plunger/actuator at the brake pedal. Ensure it's depressed when the pedal is released and released when the pedal is pressed. Adjust if necessary.
3. Continuity Test: Locate the brake light switch (usually above the brake pedal). Disconnect its electrical connector. Using a multimeter, check for continuity across the switch terminals. There should be continuity when the pedal is pressed (switch activated) and no continuity when the pedal is released (switch deactivated).
4. Power Check: Check for 12V at the input side of the switch.
Repair Procedures:
1. Replace Fuse/Bulbs.
2. Adjust Switch: If it's physically out of position.
3. Replace Brake Light Switch: If it fails the continuity test.
4. Repair Wiring: Fix loose connections or broken wires.
I. Indicator (Turn Signal)
System Function: Signals turning intentions to other road users. Includes the flasher unit, indicator switch, and bulbs.
Common Faults:
1. No indicators working: Blown fuse, faulty flasher unit, faulty indicator switch, open circuit.
2. Indicators flash too fast: Indicates a blown bulb in that circuit (due to reduced load, the flasher unit speeds up).
3. Indicators flash too slow or stay on: Faulty flasher unit, poor ground connection, high resistance in the circuit.
4. Only one side/some indicators working: Blown bulb(s) on the affected side, open circuit to those bulbs, or faulty wiring.
5. Hazard lights work but turn signals don't (or vice versa): Points to a fault specifically in the turn signal switch or wiring, as hazard lights often bypass parts of the turn signal circuit.
Diagnostic Steps:
1. Check Fuse: Inspect the indicator/hazard fuse.
2. Bulb Inspection: Visually inspect all indicator bulbs (front, rear, side repeaters). Replace any blown bulbs.
3. Flasher Unit Test: Listen for the clicking sound of the flasher unit when indicators are activated. No click usually means a faulty flasher or no power to it. Swap the flasher unit with a known good one if available. Check for 12V power at the flasher unit terminals.
4. Indicator Switch Test: Use a multimeter to check continuity across the switch terminals in different positions (left, right, off). Refer to wiring diagram.
5. Wiring Check: Trace wiring from flasher to switch, and switch to individual bulbs. Check for continuity and shorts.
Repair Procedures:
1. Replace Blown Fuse/Bulbs.
2. Replace Flasher Unit: If diagnosed faulty.
3. Repair/Replace Indicator Switch: Clean contacts or replace the switch.
4. Repair Wiring/Connections: Clean corroded terminals, tighten loose connections, repair broken wires.
J. Door Switch Function: Detects whether a door is open or closed. Used for dome lights, door ajar warnings, security systems.
Common Faults:
1. Dome light stays on/doesn't come on: Faulty switch (stuck open/closed), wiring issue, faulty bulb.
2. Door ajar warning on/off incorrectly: Faulty switch.
3. Security system malfunction related to door: Faulty switch.
Diagnostic Steps:
1. Visual Inspection: Locate the door switch (often a plunger type in the door jamb or a rotary type within the latch mechanism). Check for physical damage or sticking.
2. Continuity Test: Disconnect the switch. Check continuity across the terminals. For a typical plunger
Job Creation and Entrepreneurship: The skills learned in diagnosing and repairing these auxiliary units are directly applicable to becoming a professional auto electrician or mechanic. In Nigeria, the demand for skilled technicians is high, especially for maintaining the large fleet of vehicles (both private and commercial) found across cities like Lagos, Abuja, and Port Harcourt. Graduates can set up their own workshops, providing essential services to their communities and contributing to the local economy.
Vehicle Safety and Roadworthiness: Many of the components covered (e.g., brake lights, indicators, horn, wipers) are critical for vehicle safety. A non-functional horn or faulty brake lights significantly increases the risk of accidents on busy Nigerian roads. By being able to repair these, students contribute directly to road safety, reducing accidents and protecting lives. This knowledge is also crucial for vehicle pre-purchase inspections and roadworthiness certifications.
Cost Savings and Maintenance: For vehicle owners, understanding these basic diagnostics can lead to significant cost savings. Instead of replacing an entire unit for a minor fault (like a blown fuse or corroded terminal), a skilled individual can perform a precise repair. This is particularly relevant in Nigeria where genuine spare parts can be expensive or hard to find, making repair a more economical option. It also fosters a culture of proper vehicle maintenance rather than simply waiting for complete breakdown.