#vehicle systems

What the four strokes actually cost and earn, why compression ratio is the single number that sets efficiency and why knock caps it, how bore, stroke and swept volume are related, and why a four cylinder shakes in a way a straight six does not.

What a cam lobe actually controls, why OHV, SOHC and DOHC differ in more than layout, how lift, duration and overlap trade idle quality against top end breathing, and what cam phasing, lift switching and camless systems each solve.

Why moving the injector from the port into the cylinder raises compression ratio and fuel pressure by two orders of magnitude, what stratified charge buys and costs, why GDI engines make soot and need a particulate filter, and how lambda control and fuel trims actually work.

Why an engine that makes useful torque over 3,000 rpm needs six ratios to move a car from rest to motorway speed, how tractive effort and road load set the gearing, and what manual, torque converter, DCT and CVT each trade away.

What camber, caster, toe, kingpin inclination and scrub radius each actually do, why unsprung mass matters more than its weight suggests, how weight transfer and roll centres set the handling balance, and what understeer really is.

How a 250 newton push on a pedal becomes tens of kilonewtons at the pads, why brake fluid absorbs water and what that does to the pedal, why ABS works the wheels at ten to twenty per cent slip rather than locking them, and how weight transfer decides the front to rear split.

Why a vehicle uses the body as half of every circuit, why voltage drop and not resistance is the measurement that finds electrical faults, what a fuse actually protects, why relays exist, and how parasitic draw is tested.

What cold cranking amps and reserve capacity actually measure, how open circuit voltage reveals state of charge, why stop-start vehicles need AGM or EFB and a battery sensor, how an alternator makes DC from three phases, and how to test a starter circuit properly.

The four kinds of signal an engine control unit reads, why a thermistor is non-linear, what MAP and MAF each actually measure, the real difference between inductive and Hall effect position sensors, and why modern sensors have gone digital.

How a control module makes something happen — solenoids and their inductive kick, why pulse width modulation replaced the resistor, duty cycle as a command, H-bridges for reversible motors, and what closed-loop position control adds.

Why two twisted wires replaced a loom, how dominant and recessive bits let modules arbitrate without a master, what the 120 ohm terminators are for, and the handful of measurements that tell you whether a network is healthy.

Why one network was never going to be enough — LIN for cheap slow things, FlexRay for deterministic ones, Automotive Ethernet for cameras and updates, and how a gateway and a domain architecture hold them all together.

How the engine, motor, battery and wheels are arranged in series, parallel and power-split hybrids, what changes in a pure battery vehicle, and why the layout decides what the vehicle is good at long before any component is sized.

Why an EV traction system is deliberately isolated from the body rather than earthed to it, how the interlock loop and isolation monitor work, and the shutdown sequence that has to be followed before anyone opens an orange cable.

What separates LFP from NMC and NCA, why cell format changes how a pack is cooled and repaired, how cells become modules and packs, and what thermal runaway actually is.

How a BMS estimates state of charge when it cannot measure it directly, what state of health really means, why cells drift apart and how balancing pulls them back, and what the thermal circuit is protecting.

How a three-phase inverter turns DC into a rotating field, what separates a permanent magnet machine from an induction or reluctance one, why silicon carbide is displacing IGBTs, and where the limits of regenerative braking actually lie.

Why AC charging is limited by what is in the car and DC charging is not, what the connectors and their signalling pins actually do, why a charge curve tapers, and what ISO 15118 makes possible including bidirectional power.

What radar, lidar, cameras and ultrasonic sensors each measure directly, where each one fails, and why no single sensor is trusted alone on a vehicle that has to work in fog, glare and rain.

How separate sensor views become one picture, what a Kalman filter is actually doing, where learned perception differs from hand-written rules, and what the SAE levels really divide on.

How adaptive cruise, autonomous emergency braking and lane keeping actually decide to act, why false positives matter more than they sound, and what drive-by-wire has to guarantee underneath all of it.

Why a vehicle that can talk to other vehicles and to the roadside sees things no sensor can reach, how DSRC and C-V2X differ, and why the hardest part of the problem is trust rather than radio.

Why the industry moved from a hundred small controllers to a handful of big ones, what zonal wiring actually saves, how an over-the-air update is made safe to interrupt, and what ISO/SAE 21434 requires of the organisation rather than the product.

What a diagnostic trouble code actually tells you and what it does not, why freeze frame is usually worth more than the code itself, and what readiness monitors are really testing.

The request and response structure of ISO 14229, the services worth knowing by number, why a negative response is often more useful than a positive one, and what seed and key does and does not protect.

What a scope shows that a scan tool and a multimeter cannot, how a healthy CAN pair should look, the four faults that account for most bus problems, and why voltage drop beats resistance every time.

Why a replaced windscreen means a calibration, what a static bay actually has to guarantee, why the thrust line and not the body centreline is the reference, and how a fraction of a degree becomes a metre.

Why a crumple zone is a distance and not a cushion, how a soft front and a hard cell work together, what a pretensioner and a load limiter each do, and the millisecond timeline an airbag has to hit.

How a hazard analysis turns severity, exposure and controllability into an integrity level, what ASIL D actually obliges you to do, why decomposition without independence is fiction, and where functional safety stops and SOTIF begins.