Steering/ Suspension
HVAC
Elec.
Brakes
Diesel Engines
100

A driver reports that their heavy truck pulls strongly to the right while driving straight on a level road. What are three possible causes, and how would you diagnose the problem?

  • Uneven tire pressure: Check all tire pressures; underinflated tires on one side cause pulling
  • Wheel misalignment: Use a wheel alignment machine to check toe-in, camber, and caster angles
  • Brake dragging: Inspect brake components on the left side for sticking calipers or stuck brake shoes
  • Worn suspension components: Check tie rods, ball joints, and control arms for excessive wear or damage
100

What are the four main components of an automotive air conditioning system?

Compressor, condenser, expansion valve (or orifice tube), and evaporator

100

What does the starter motor do?

 It uses electrical power from the battery to crank and start the engine

100

 A driver reports that the air brakes on their heavy truck feel "spongy" and require extra pedal pressure to stop the vehicle. The truck takes longer to stop than normal. What are the possible causes, and how would you diagnose the issue?

  • Air leak in the system: Listen for hissing sounds; use soapy water to identify leaks in brake lines, fittings, hoses, or brake chambers. Check that the air pressure builds to normal operating range (85-100 PSI)
  • Moisture in the air system: Drain the air tanks and check for water; install or replace the air dryer cartridge if contaminated
  • Faulty brake chamber diaphragm: Perform a brake chamber test; if air pressure doesn't hold, replace the brake chamber
  • Worn brake pads or shoes: Inspect brake linings for wear; if thickness is below minimum, replace brake shoes/pads
  • Slack adjuster out of adjustment: Check brake rod stroke; if excessive, adjust the slack adjuster or replace if worn
  • Compressor not building pressure: Check compressor output; if low, repair or replace the compressor
100

 A fleet manager notices that one of the diesel trucks hasn't had an oil change in 8 months, even though it's been running regularly. The driver says the oil still looks clean. What should the manager do and why?

Answer: The manager should schedule an immediate oil change regardless of appearance. Here's why:

  • Diesel engines require regular oil changes based on time intervals OR mileage, whichever comes first
  • Oil degrades over time even if it looks clean—oxidation and acid buildup occur internally
  • Diesel engines produce more soot and byproducts than gasoline engines, contaminating oil faster
  • Standard intervals: typically 7,500-15,000 miles or every 6 months (check manufacturer specs)
  • Skipping scheduled maintenance voids warranties and risks engine damage, sludge buildup, and reduced fuel efficiency
200

During a pre-trip inspection, you notice the truck's cab bounces excessively after hitting a bump and takes several seconds to settle. The vehicle has an air suspension system. What could be the problem, and what should you check?


  • Worn shock absorbers or dampers: They're not controlling the bounce; replace them
  • Air suspension leak: Check for hissing sounds, inspect air lines and bellows for cracks or holes; repair or replace
  • Faulty leveling valve: Not maintaining proper suspension height; may need adjustment or replacement
  • Low air pressure in the system: Check compressor operation and air tank for leaks; recharge if needed
  • Worn suspension bushings: Check rubber mounts for deterioration
200

 Where does the heat come from in a car's heating system?

Hot engine coolant that flows through the heater core

200

What is the standard voltage of a typical automotive electrical system?

12 volts (in most modern vehicles)

200

 During a pre-trip inspection on a dual-circuit air brake system, you notice that when you apply the brakes, only the rear wheels lock up while the front wheels continue rolling. What is the problem, and what should you check?

  • Front brake circuit failure: The front brake circuit has lost air pressure; check for leaks in the front brake lines, hoses, or fittings
  • Front brake valve malfunction: The front brake control valve is not responding to pedal input; test and replace if faulty
  • Front brake chambers damaged or disconnected: Inspect for cracks, disconnected air lines, or failed diaphragms; repair or replace
  • Proportioning valve failure: On some systems, this valve distributes pressure between front and rear; if faulty, it prevents front braking
  • Brake pedal linkage issue: Check that the brake pedal is properly connected to the brake valve and moving freely
  • Immediate action: Take the vehicle out of service; the braking system is unsafe and must be repaired before operation
200

A diesel engine is running rough, has reduced power, and starts harder than usual. The mechanic suspects a fuel filter issue. What steps should be taken, and why is this critical for diesel engines?

Answer: 

Steps:

  1. Inspect and replace the fuel filter immediately
  2. Bleed air from the fuel system after replacement
  3. Check for water contamination in the fuel tank

Why this matters for diesel engines:

  • Diesel fuel contains more particles and contaminants than gasoline
  • Clogged fuel filters restrict fuel flow, causing poor combustion and rough running
  • Diesel engines are sensitive to water in fuel—it causes corrosion, injector damage, and can lead to engine failure
  • Fuel filters should be changed every 10,000-15,000 miles or as indicated by warning lights
  • Air in the fuel system prevents proper fuel delivery and can damage the fuel pump
300

A heavy vehicle's steering wheel is hard to turn, especially when parked or at low speeds. The power steering system is equipped. What are the most likely causes?

  • Low power steering fluid level: Check reservoir and top off; inspect for leaks in hoses and connections
  • Power steering fluid contamination: Dirty fluid reduces hydraulic pressure; flush and replace fluid
  • Faulty power steering pump: Not producing adequate pressure; may need repair or replacement
  • Steering gear problems: Internal wear or damage reducing assist; may need rebuilding or replacement
  • Tight steering linkage or tie rods: Excessive friction from wear or misalignment; inspect and replace worn components
  • Engine idle too low: Power steering pump needs minimum RPM to function; adjust idle speed
300

What does the blend door do?

 It mixes hot air from the heater core with cold air from the evaporator to control the cabin temperature

300

What is the purpose of the alternator?

To generate electricity and recharge the battery while the engine is running

300

A heavy vehicle's air pressure gauge shows that the compressor is continuously running and air pressure fluctuates between 70-85 PSI instead of holding steady at 95-100 PSI. The driver also notices the "low air" warning light flickering. What are the likely causes?

  • Air leak in the system: Check all brake lines, hoses, fittings, and brake chambers with soapy water; tighten or replace as needed
  • Faulty air dryer: The dryer cartridge may be clogged or saturated with moisture; replace the cartridge and drain the air tanks
  • Worn compressor: Compressor may not be building pressure efficiently; perform a compressor test; repair or replace if necessary
  • Leaking brake chamber diaphragm: One or more brake chambers may have a ruptured diaphragm; perform a leak test on each chamber and replace as needed
  • Faulty air tank drain valve: May not be sealing properly; replace the valve
  • Governor valve malfunction: The governor controls when the compressor stops; if faulty, it won't allow proper pressure buildup; test and replace if needed
300

A construction company's diesel excavator begins overheating during normal operation. The coolant level is low, and there's a slight sweet smell near the engine. What could be happening, and what maintenance steps are needed?

Answer: Likely Issue: Coolant leak and/or head gasket failure (the sweet smell suggests coolant burning in combustion chambers)

Maintenance steps:

  1. Stop operation immediately—continuing to run risks catastrophic engine damage
  2. Inspect hoses, connections, and radiator for visible leaks
  3. Check the oil dipstick—if oil appears milky, this confirms coolant mixing with oil (head gasket failure)
  4. Repair or replace damaged hoses and connections
  5. If head gasket is failed, professional engine work is required
  6. Refill with proper diesel engine coolant (not car coolant—different additives)
  7. Bleed air from the cooling system

Prevention: Check coolant level weekly and inspect hoses during routine maintenance

400

 A driver complains that the truck's rear end feels unstable and sways excessively when turning or braking. The vehicle has a leaf spring suspension. What should you inspect to identify the problem?

  • Worn leaf springs: Check for broken leaves, cracks, or sagging; springs may have lost their ability to control lateral movement
  • Damaged or worn shock absorbers: Test by pushing down on the chassis; should return smoothly without excessive bouncing
  • Worn or loose suspension bushings: Inspect rubber mounts and U-bolts for wear, cracks, or looseness
  • Broken or loose sway bar components: Check sway bar links and bushings for damage; tighten or replace as needed
  • Tire wear patterns: Look for uneven wear indicating alignment or suspension issues
  • Overloaded cargo: Verify load distribution; excessive weight can cause instability
400

 If a customer says their A/C works for a few minutes then blows warm air, what is the most likely cause?

Low refrigerant charge, which causes the compressor clutch to cycle on and off

400

 What are the three main components of a basic automotive electrical system?

Battery, alternator, and starter motor

400

A driver reports that the service brakes work fine, but the spring brakes (emergency/parking brakes) won't release. The truck is immobilized and cannot be moved. What should you check to diagnose and fix this problem?

  • Low air pressure: Check the air pressure gauge; if below 60-70 PSI, the spring brakes will engage. Build air pressure by running the engine and allowing the compressor to refill the system
  • Spring brake release valve stuck: Inspect the valve for damage or corrosion; clean or replace if necessary
  • Faulty spring brake chamber: The diaphragm may be ruptured or the spring may be broken; perform a visual inspection and replace the chamber if damaged
  • Air line disconnected or blocked: Check that air lines to the spring brake chambers are connected and not kinked or blocked; reconnect or clear as needed
  • Brake pedal linkage issue: Ensure the brake pedal is functioning properly and can fully release; check for mechanical obstructions
  • Compressor failure: If the compressor won't build pressure, the system cannot release the spring brakes; repair or replace the compressor
  • Immediate action: Do not attempt to tow the vehicle until spring brakes are released; call for roadside assistance if needed
400

A farming operation has been running a diesel tractor for 2 years without replacing the air filter. The engine now has reduced power, increased fuel consumption, and black smoke in the exhaust. What's the problem and how should it be addressed?

Answer: The Problem:

  • A severely clogged air filter restricts airflow to the engine
  • This creates a rich fuel mixture (too much fuel, not enough air)
  • Incomplete combustion results in black smoke, reduced power, and wasted fuel
  • Carbon buildup damages the engine over time

How to address it:

  1. Replace the air filter immediately
  2. Inspect the engine air intake system for additional debris
  3. Check the turbocharger (if equipped) for carbon buildup
  4. Monitor fuel consumption and performance to confirm improvement
  5. Going forward: Replace air filters every 15,000-30,000 miles depending on operating conditions (dusty environments need more frequent changes)

Cost-benefit: A $20-50 air filter prevents thousands in engine repairs

500

After routine maintenance, a technician notices the steering wheel is off-center (not straight) when the wheels are pointing straight ahead. The driver also reports the vehicle pulls slightly to the left. What is the likely cause, and how should this be corrected?

  • Likely cause: Wheel alignment was performed incorrectly, or steering linkage components were disturbed during service
  • Correction steps:
    • Perform a complete wheel alignment check (toe-in, camber, caster on front wheels; toe-in on rear wheels)
    • Verify all tie rod lengths are equal and properly adjusted
    • Check that the steering gear is centered and the steering wheel is properly installed on the steering shaft
    • Adjust toe-in on both sides equally to center the steering wheel
    • Perform a road test to confirm proper steering response and straight-line tracking
    • Document all alignment measurements for the vehicle's records
500

What is the typical low-side pressure range in a functioning A/C system?

20-40 PSI

500

A customer's dashboard warning light shows a battery symbol. What does this typically indicate?

The alternator is not charging the battery properly, or there's an issue with the charging system

500

After replacing brake shoes on a heavy vehicle, the driver reports that one wheel locks up during braking while the others release normally. The vehicle pulls to one side when braking. What could have gone wrong during the repair, and how would you correct it?

  • Brake shoe installed incorrectly: Check that the new brake shoes are installed with the correct orientation (leading and trailing shoes); reinstall if reversed
  • Slack adjuster not properly adjusted: The wheel with the locking brake may have excessive brake rod stroke; adjust the slack adjuster so brake rod stroke is within specification (typically 1.5-2 inches)
  • Contaminated brake linings: Oil or grease on the new brake shoes reduces friction; clean or replace the shoes
  • Brake drum damage: Check the drum for cracks, scoring, or excessive wear; if damaged, replace the drum
  • Faulty brake chamber on that wheel: The chamber may not be releasing properly; test for air leaks or diaphragm damage; replace if necessary
  • Incorrect brake shoe material: Verify that the replacement shoes match the original specifications for the vehicle; install correct shoes if wrong type was used
  • Brake valve imbalance: The brake valve may not be distributing pressure evenly; test and adjust the proportioning valve if applicable
  • Correction process: Readjust the slack adjuster, verify proper brake shoe installation, perform a brake test, and road test to confirm even braking on all wheels
500

A delivery company's diesel trucks won't start on a cold morning in January. The fuel lines appear blocked, but fuel is present in the tank. What's happening, and how should the maintenance team respond?

Answer: The Problem: Fuel Gelling

  • In cold temperatures, diesel fuel can gel or thicken because of paraffin crystals forming
  • This blocks fuel lines and prevents fuel from reaching the engine
  • This is especially common below 32°F (0°C)

Immediate response:

  1. Move the vehicle to a warm location if possible
  2. Use engine block heaters to warm the engine
  3. Replace with winter-grade diesel fuel (blended with additives to prevent gelling)
  4. Use fuel additives specifically designed for cold-weather diesel operation

Preventive maintenance:

  • Switch to winter-grade diesel (typically September-March in cold climates)
  • Install and use block heaters in winter
  • Add fuel anti-gel additives to the tank
  • Keep fuel tanks as full as possible to reduce condensation
  • Store vehicles in heated garages when possible
  • Check fuel filters more frequently in winter (they clog faster with gelled fuel)
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