Car technology, explained

Engines: what the badges and numbers mean

An engine's size, power and torque each tell you something different. Badges such as TSI or EcoBoost are marketing names, so it helps to know what sits behind them.

Engine size

Given in litres or cc, it is the combined volume of the cylinders, so a 1.0-litre engine is about 1,000cc. A bigger engine is not automatically faster or thirstier, because a turbocharger changes the picture.

Turbocharger

A small turbine, spun by exhaust gas, that pushes extra air into the engine. It lets a small engine make the power of a larger one. Ford's 1.0-litre three-cylinder EcoBoost petrol in the Fiesta is turbocharged.

Badges

TSI (petrol) and TDI (diesel) are Volkswagen Group names for turbocharged engines, and eTSI is its mild-hybrid petrol. EcoBoost is Ford's turbocharged petrol family and TDCi was a Ford diesel badge. Each maker has its own names, so check the handbook for what a specific badge means.

Power

How quickly the engine can do work. Makers quote it as PS, bhp, hp or kW. The units are close but not identical, which is why our car guides keep the unit the source used rather than converting.

Torque

Twisting force, measured in Nm. High torque at low revs is what makes a car feel strong pulling away or overtaking. Turbo petrols and diesels tend to be strong here.

Petrol or diesel

Diesels tend to use less fuel per mile, especially on longer runs, but they carry exhaust filters that dislike short trips (see diesel exhaust systems). Petrol often suits mostly short journeys better.

Cambelt or chain

Many engines time their valves with a rubber belt that has a replacement interval in miles and years. Others use a chain meant to last longer. Either way, ask for proof of the last change. A belt failure can be expensive: Auto Express says a Fiesta cambelt failure can cost at least £1,000 to fix.

See it on a car guide: Ford Fiesta (turbo petrol, mild hybrid and diesel); Volkswagen Golf (TSI, eTSI and TDI).

Hybrids: mild, full and plug-in

"Hybrid" covers three quite different things. What matters is whether the electric motor can move the car and whether you ever plug it in.

Mild hybrid (MHEV)

A small battery and motor-generator assist the engine, for example letting it switch off earlier when coasting. It cannot drive the car on its own. The mild-hybrid versions of the Ford Fiesta's 1.0 EcoBoost and the Volkswagen Golf eTSI are examples, and Parkers says the Fiesta system will not dramatically cut running costs.

Full hybrid (HEV)

A larger battery and motor can move the car on electricity alone, usually for short distances at low speed. The engine and braking recharge the battery, so you never plug it in. Every current Toyota Yaris is a self-charging full hybrid.

Plug-in hybrid (PHEV)

A bigger battery that you charge from a socket, with a petrol engine as back-up. The Golf eHybrid is an example. It makes most sense if you plug in regularly and your trips are short. The quoted electric range comes from a laboratory test, so expect less in real use.

Battery electric (BEV)

No engine at all. See electric cars: batteries, range and charging.

See it on a car guide: Toyota Yaris (full hybrid); Ford Fiesta (mild hybrid); Volkswagen Golf (mild and plug-in hybrid).

Gearboxes: manual, automatic, DSG and CVT

Two cars with the same engine can feel completely different depending on the gearbox. The type also affects what can go wrong and what service history to ask for.

Manual

You choose the gear with a clutch pedal. It is the simplest design, and the clutch is a wear item that eventually needs replacing.

Conventional automatic

A fluid coupling (torque converter) and sets of gears change ratio for you. Usually smooth, and a common choice on larger cars.

Dual-clutch (DSG, DCT, Powershift)

Two clutches, one for odd gears and one for even, so the next gear is ready before it is needed. Shifts are quick. DSG is Volkswagen Group's name for it and Powershift is Ford's. Designs differ, and some have reputations for hesitation or failure: Auto Express says the Fiesta's Powershift automatic can fail.

CVT

A continuously variable transmission has no fixed gears and varies the ratio smoothly. It can be quiet in gentle driving but the engine may rev high and sound strained under hard acceleration. carwow reports this on the Toyota Yaris hybrid, which uses a CVT automatic.

Electric cars

Most have no gear changes at all, only a single fixed reduction ratio, so acceleration is smooth.

See it on a car guide: Volkswagen Golf (DSG); Ford Fiesta (Powershift); Toyota Yaris (CVT); Skoda Karoq (DSG).

Driver aids: what they do and what they do not

Driver assistance systems use cameras, radar and sensors to warn you or to help with braking, steering and speed. They are aids. The driver stays responsible, and none of them makes a car self-driving.

Automatic emergency braking (AEB)

Warns you of a likely collision ahead and can brake if you do not. What it detects varies: some systems react to cars only, while others also detect pedestrians and cyclists. The Volkswagen Golf's system detects both, according to Euro NCAP.

Adaptive cruise control

Holds a set speed and keeps a gap to the vehicle in front, slowing and speeding up as needed.

Lane departure warning and lane-keeping assist

The first warns you when you drift out of lane. The second also steers gently back. Neither replaces your attention.

Blind-spot monitoring and parking sensors

Warn of vehicles beside you or obstacles near the bumpers when parking.

Speed assistance

Reads road signs and can warn you or limit speed. It can be wrong, so check the sign yourself.

Same model, different equipment

Whether a system is standard, optional or not offered depends on the model year and trim. Euro NCAP gave the 2017 Ford Fiesta it tested no credit for automatic emergency braking because it was optional, so whether a particular Fiesta has it depends on what the first owner chose.

Keeping them working

Sensors need to be clean and correctly aimed. After a windscreen replacement or a front bumper repair, cameras and radar can need recalibrating, so ask what was done and for any paperwork. A dashboard warning about a sensor or assist system should be understood before you buy.

See it on a car guide: Ford Fiesta (optional on the tested car); Volkswagen Golf (Travel Assist); Toyota Yaris (standard from Icon trim).

Euro NCAP: how to read a safety rating

Euro NCAP is a European car safety organisation that crash-tests new models and publishes star ratings with percentage scores. It is a useful guide, provided you know what a rating does and does not cover.

What the scores mean

Our car guides quote the percentages Euro NCAP published for each test: how well the car protected adults and children in a crash, how well it protected pedestrians and other vulnerable road users, and how good its driver-assistance systems were (safety assist). Higher is better in each area, and five stars is the top rating.

Read it with care

• Check the year. Euro NCAP makes its tests stricter over time and has changed how it groups and scores them. A five-star rating from one year is not like-for-like with five stars from another. The Volkswagen Golf was rated in 2019 and again in 2025, with different percentages in each.
• Check the version tested. A rating applies to the equipment on the car Euro NCAP tested. If a safety feature was optional, your car may not have it.
• Older ratings can expire. Euro NCAP's website lists the 2017 Ford Fiesta and Skoda Karoq ratings as expired from 1 January 2024. An expired rating is not a safety defect, but it is a reminder that the test is old.
• It is not about reliability. A rating says how a car performs in a crash and how good its safety technology is. It says nothing about how often the car fails an MOT. For that, see the DVSA pass rates in our car guides.

See it on a car guide: Ford Fiesta (2017, five stars); Volkswagen Golf (2019 and 2025); Toyota Yaris (2020 and 2025); MG4 (2022); Skoda Karoq (2017).

Electric cars: batteries, range and charging

Electric car specifications look intimidating, but a handful of terms cover most of them.

kWh and kW

A kilowatt-hour (kWh) is an amount of energy, like the size of a fuel tank. A kilowatt (kW) is power, the rate that energy flows in or out. What Car? lists the MG4 Long Range with a 61.7 kWh battery that can charge at up to 135 kW: the first figure is how much energy it holds and the second is how fast it can take energy in. Some makers quote a gross battery size and a smaller usable one, so check which number you are reading.

Range

The official WLTP range comes from a laboratory test. Real-world range is usually lower, and falls at motorway speeds and in cold weather. Use the official figure to compare cars and a cautious figure to plan journeys.

AC and DC charging

AC charging, at home or on slower public chargers, uses the car's onboard charger. A typical home wall box is around 7 kW. DC rapid chargers feed the battery directly and are much faster, limited by the car's own maximum DC rate. The time to charge from 10% to 80% tells you more than a peak figure that lasts only briefly.

Plugs

New electric cars in the UK use a Type 2 plug for AC and CCS for DC rapid charging. Some older cars, such as earlier Nissan Leafs, use CHAdeMO for rapid charging, so check that a charger fits before you rely on it.

Battery chemistry

LFP (lithium iron phosphate) and NMC (nickel manganese cobalt) are two common types. A single model can use both: Wikipedia says the smallest MG4 pack uses LFP cells and the larger packs use NMC. Follow the maker's charging advice for the specific car.

Battery health

Batteries lose some capacity as they age. On a used car, ask for a battery health report. Makers' battery warranties usually cover a set number of years and miles, but the terms vary, so read them and check whether they pass to a second owner.

See it on a car guide: MG4 (LFP and NMC versions).

Screens, phone connection and software

The screen is the part of the car you use every day, and it can date quickly. These are the terms you will meet.

Apple CarPlay and Android Auto

Show phone apps, maps and music on the car's screen. Some cars connect with a cable and others wirelessly, so check which. Many cars rely on the phone for navigation: carwow says no Toyota Yaris trim has built-in sat nav, but CarPlay and Android Auto are standard.

Built-in sat nav

Works without a phone, but the maps can go out of date. Ask whether they can still be updated, and what it costs.

Software updates

Some cars update over the air, like a phone. Others need a dealer visit. Auto Express says Fiesta infotainment faults are usually cured by a software update.

Connected services

Features such as a phone app, live traffic or remote locking may be free for a trial period and paid afterwards. Check what still works on the car and what it costs.

Emergency call

Many newer cars have a built-in emergency call function. carwow lists an emergency-call fault among the Toyota Yaris recalls, so it is worth checking a car's recall status.

Usability counts

What Car? calls the MG4's screen fiddly because most climate controls sit inside it. On a test drive, check that you can adjust temperature, fan and demisting without taking your eyes off the road for long.

See it on a car guide: Toyota Yaris (CarPlay and Android Auto standard); MG4 (climate controls in the screen); Ford Fiesta (software updates).

Diesel exhaust systems: DPF, EGR and AdBlue

Modern diesels carry equipment that cleans the exhaust. It works well when the car is used as designed and can be costly when it is not.

DPF (diesel particulate filter)

A filter that traps soot. It cleans itself by burning the soot off when the exhaust is hot enough, which needs a longer run at a steady speed. Lots of short trips can stop that happening, and a warning light may appear. What Car? reports costly diesel particulate filter faults on the Skoda Karoq diesel.

EGR valve

Feeds some exhaust gas back into the engine to lower combustion temperature and reduce nitrogen oxides. It can clog with soot over time.

AdBlue (SCR)

A urea solution, stored in its own tank, that is sprayed into the exhaust to cut nitrogen oxides. It needs topping up. Many cars warn well before it runs out, and some will not restart once it is empty, so do not ignore the warning. The Volkswagen Golf TDI uses AdBlue treatment.

What the MOT says

DVSA tells testers to fail a car if a DPF that was fitted as standard has been removed. Since 20 May 2018, GOV.UK says a car also gets a major fault if the tester finds evidence that the DPF has been tampered with, or if the tester can see smoke of any colour coming from the exhaust.

Emissions rules beyond the MOT

The Euro standard a car meets decides whether it is charged in city clean air zones. Our guides to Euro emissions standards and ULEZ cover it, and UK green zones lists the cities and charges.

See it on a car guide: Volkswagen Golf (TDI with AdBlue); Skoda Karoq (diesel reliability).

Sources: GOV.UK: MOT changes 20 May 2018; DVSA: inspecting diesel particulate filters.

Technology on each car guide

Search any of our 50 models in the car finder to see its MOT pass rate, age comparison and what to check. A Technology section, with engines, safety ratings, infotainment and known issues, each attributed to a source, is live for: Ford Fiesta, MG4, Skoda Karoq, Toyota Yaris, Volkswagen Golf. We add models over time.

Explainers last checked October 2026. Technology changes quickly, so check the details of the specific car in front of you.