Vehicle systems
Each system: what it does, the parts in it, and what usually goes wrong.
Engine
Turns fuel and air into rotation. Everything else either feeds it, cools it, or uses what it produces.
Parts
Engine block · Pistons · Connecting rods · Crankshaft · Engine mounts · Cylinder head · Camshafts · Valves · Timing belt or chain · Valve cover & gasket · Head gasket · Air filter & box · Mass airflow sensor · Throttle body · Intake manifold · Turbocharger · Intercooler · Spark plugs · Ignition coils · Oil pan · Oil pump · Oil filter · PCV valve · Serpentine belt & tensioner · Crankshaft position sensor · Camshaft position sensor · Coolant temperature sensor · Knock sensor
What usually fails
- Cracks from severe overheating or freezing with weak coolant
- Worn piston rings letting oil past
- Worn rod bearings from oil starvation
- Worn main bearings
- Cracked or collapsed rubber
Electric drive
On hybrids and EVs: the high-voltage battery, the motor that drives the wheels, and the electronics between them.
Parts
High-voltage battery · Electric drive motor · Inverter / power electronics
What usually fails
- Gradual capacity loss
- Bearing wear
- Overheating from coolant pump failure
Cooling
Keeps the engine at its working temperature by moving coolant through the engine and the radiator.
Parts
Radiator · Cooling fans · Water pump · Thermostat · Radiator hoses · Coolant reservoir
What usually fails
- Leaks at the plastic end tanks or seams
- Failed motor
- Seal leaking from the weep hole
- Stuck open: engine never fully warms
- Soft, swollen or cracked rubber
Fuel
Stores fuel at the back of the car and delivers it, under pressure, to the injectors at the front.
Parts
Fuel tank · Fuel pump · Fuel filter · Fuel lines · Fuel injectors & rail
What usually fails
- Damaged or loose straps
- Worn pump losing pressure
- Clogging on high mileage or after bad fuel
- Corrosion in salt-belt states
- Clogged or dribbling injectors
Exhaust & emissions
Carries burnt gases away from the engine, cleans them, quiets them, and captures fuel vapor.
Parts
Exhaust manifold · Upstream oxygen sensor · Catalytic converter · Downstream oxygen sensor · Resonator · Muffler · Exhaust piping · EGR valve · EVAP canister & purge valve
What usually fails
- Cracks from heat cycles
- Slow response with age
- Worn out by misfires, oil or coolant burning
- Failed heater
- Rust-through
Transmission & drivetrain
Takes the engine's rotation, picks a gear ratio, and sends it to the wheels that drive the car.
Parts
Transmission · Torque converter · Clutch · CV axles & joints · Driveshaft · Differential · Transfer case
What usually fails
- Worn clutches or bands
- Lock-up clutch shudder
- Worn friction disc
- Torn rubber boot letting grease out and dirt in
- Worn universal joints
Brakes
Your foot pushes fluid; the fluid squeezes pads against spinning discs at each wheel.
Parts
Brake rotor · Brake pads · Brake caliper · Brake lines & hoses · Parking brake · Brake booster · Master cylinder · ABS module
What usually fails
- Wear below minimum thickness
- Normal wear
- Seized slide pins
- Rust on steel lines (salt states)
- Seized or stretched cables
Suspension
Holds the wheels against the road and absorbs bumps so the body stays steady.
Parts
Struts (front) · Coil springs · Shock absorbers (rear) · Control arms · Ball joints · Sway bar & end links · Bushings · Wheel hub & bearing
What usually fails
- Worn damper (oil leaking down the body)
- Corrosion and breakage at the ends
- Leaking oil
- Worn bushings
- Wear and play
Steering
Turns the small motion of your hands into the large motion of the front wheels.
Parts
Steering wheel · Steering column · Steering rack · Tie rods · Power steering assist
What usually fails
- Worn clock spring (the ribbon that carries wiring to the airbag and buttons)
- Worn intermediate shaft joint
- Leaking seals (hydraulic)
- Worn outer end
- Low or old fluid, leaking hoses, worn pump (hydraulic)
Wheels & tires
The only parts that touch the road. Everything the car does passes through four hand-sized patches of rubber.
Parts
Tires · Wheels · Tire pressure sensors
What usually fails
- Tread wear and age cracking
- Bent from potholes
- Internal battery dying after several years
Electrical
Stores, makes and distributes electricity, and runs the computers that control everything else.
Parts
12-volt battery · Alternator · Starter motor · Fuse box · Wiring harness · Control modules
What usually fails
- Age (3–6 years is typical)
- Worn bearings
- Worn brushes or solenoid
- Blown fuses (the symptom of a fault elsewhere)
- Chafing, corrosion, rodent damage
Heating & air conditioning
Moves heat out of the cabin in summer and into it in winter.
Parts
A/C compressor · Condenser · Evaporator · Blower motor · Heater core · Cabin air filter
What usually fails
- Clutch failure
- Leaks from stone damage or corrosion
- Leaks (hard to find, deep in the dash)
- Worn motor
- Clogging
Body & safety
The structure that holds everything, protects you in a crash, and lets you see and be seen.
Parts
Unibody / frame · Hood · Doors · Bumpers & crash structures · Airbags · Seat belts · Lighting
What usually fails
- Rust, especially rocker panels and subframes in salt states
- Worn latch or cable
- Worn hinges and check straps
- Hidden damage after a minor bump
- Faulty seat occupancy sensor or clock spring