What a car is made of, and why the handbook comes first

Most car trouble gives notice first. A warning light comes on and stays on, a tyre looks a little soft, a noise turns up that wasn't there last month. Each notice means something slightly different on different cars, and the book in the glovebox (the handbook in Britain, the owner's manual in the US) is where your car's maker says what it means for this one. This lesson draws the map of a car's systems and the check that goes with each, shows why so many of the numbers you'll need can only come from that book, and sets out how the rest of the course sorts every rule and every job. The exercise has you find your own handbook and copy ten figures out of it.

That box opens every lesson in this course, word for word. Its roadside advice splits by country on purpose: British and American authorities give different first steps, and lesson 17, "Motorways and fast roads: go left, the live lane, and the smart motorway question", sets them side by side. Follow the advice for the road you're on.

It says Great Britain rather than the UK for a reason. The Highway Code on GOV.UK states: "This Highway Code applies to England, Scotland and Wales."⁵ Northern Ireland has its own version, and nidirect, its government's website, gives the reason the two differ: Northern Ireland "is largely responsible for its own road safety policy and legislation".⁷ So if you drive in Enniskillen, the Code this course quotes isn't yours, and this course has not read Northern Ireland's breakdown rules. Its own pages on nidirect are the ones to read.

Wherever this course states a law, one caution goes with it. This is general information, not legal advice. The rules differ between England and Wales, Scotland, Northern Ireland and each US state, and they change.

A car is a set of systems

The textbooks that train mechanics in the US and the UK share a core division, on this course's reading of their contents pages (the books themselves were not read): the engine, the electrical system, the brakes, steering and suspension (with tyres and wheels inside it), and the transmission. The two US books add a part on heating and air conditioning (one calls it passenger comfort), and one gives hybrid and electric vehicles a part of its own; the UK book groups brakes, steering and suspension, on this course's reading, under the part its contents call chassis systems.²⁰ That map is for people who repair cars. An owner needs a smaller one: which system each of your checks looks after. This course's map gives tyres a row of their own, because so many of the owner's checks are on them.

This is the map with the owner's part of each system filled in from GOV.UK's list and Annex 6 of the Highway Code, the part of the Code on looking after a vehicle.⁴⁶ The last column is where this course takes each one up.

Heating and air conditioning get no lesson of their own.

The last row is deliberate. In most hybrids and every electric car, the drive system runs at high voltage, and the MOT manual of the DVSA (the Driver and Vehicle Standards Agency), the rulebook for testers of the MOT, Great Britain's periodic roadworthiness test, says: "High voltage wiring insulation is orange in colour so it can be easily identified, though some imported vehicles may have high voltage wiring insulation of a different colour." It adds that "Many mild hybrids only use 48V systems which may use blue coloured insulation, rather than orange, as these are not regarded as being high voltage. However, the wiring on these systems should still be avoided."¹⁶ Nissan's handbook for the 2024 LEAF sold in the US puts the owner's part in one line: "The vehicle high voltage system has no user serviceable parts."¹⁴ The MOT manual also warns testers that on a hybrid the combustion engine "may start without warning when electrical equipment is operated or if the battery voltage drops".¹⁶ So anything on that side is Call someone, and lesson 14, "High voltage: hybrid and EV safety, charging at home, fire and flood", explains why.

Why the handbook comes first

This is general information, not legal advice.

The official sources this course read on looking after a car send you to the same book. California's Bureau of Automotive Repair (BAR), the state's regulator of garages: "Follow your owner's manual. Your vehicle owner's manual is a key resource for keeping your vehicle running its best. It includes the manufacturer's recommended maintenance schedule and other important vehicle information. It also explains your vehicle's warning lights and what to do if they come on."¹ GOV.UK, for Great Britain, says the handbook tells you how often to make each check, and "The handbook will also tell you when your vehicle needs to be serviced."⁴ The US government's fueleconomy.gov, writing about hybrids and EVs, puts the reason in one sentence: "Tips that apply to one model may not apply to another."²

The reason is that almost every figure you need is set by the car's maker for that car, and makers do not agree. The clearest case is a job all four handbooks read here cover: tightening the wheel nuts after a wheel change.

Sources: each maker's handbook for that car and market.^10111213 N·m is newton metres, the unit of torque used in the UK and Europe; lbf·ft (pound-feet) is the US unit.

The space-saver column agrees across all four. That is worth knowing, and it is still four handbooks, not yours. The coolant cap shows the same pattern. Ford's handbook for the 2024 Maverick sold in the US and Canada says not to remove the coolant cap while the system is hot and to "Wait 10 minutes for the cooling system to cool down".¹⁵ The Highway Code, for any car in Great Britain, says that if the engine overheats "you should wait until it has cooled naturally".⁶ Ten minutes is Ford's figure for a Ford. Lesson 9, "Under the bonnet: oil, coolant, brake fluid and screenwash", takes this up, and until then this course's rule is simple: never open a hot cap.

The number on the tyre, and the number on the car

Tyre pressure shows why the maker's figure wins, because the tyre carries a number too and it answers a different question.

In the US, federal law (FMVSS 110) requires the carmaker to show, "on a placard permanently affixed to the driver's side B-pillar" (the upright post the driver's door closes against), the "Vehicle manufacturer's recommended cold tire inflation pressure for front, rear and spare tires".⁸ A different federal standard, FMVSS 139, requires the tyre maker to mark each sidewall with the tyre's "maximum permissible inflation pressure", which it defines as "the maximum cold inflation pressure to which a tire may be inflated".⁹ The first is what the carmaker wants for this car. The second is the most the tyre may be inflated to when cold, on any car it is fitted to. NHTSA, the US federal road safety regulator, puts it plainly: "the correct pressure for your tire is what the vehicle manufacturer has listed, NOT what is listed on the tire itself."³

In Great Britain the Highway Code marks the same idea as a MUST rule, which means a regulation stands behind it. Annex 6 of the Highway Code: "Tyres MUST be correctly inflated to the vehicle manufacturer's specification for the load being carried. Always refer to the vehicle's handbook or data."⁶ The regulation it cites, regulation 27 of the Construction and Use Regulations, puts it more generally: a tyre must be inflated so as to be "fit for the use to which the motor vehicle or trailer is being put".²² The Code reads that as the maker's figure. TyreSafe, a UK tyre safety charity backed by tyre makers, carmakers and retailers, says to look for the figure "in your vehicle manual, on a plaque in one of the front door sills or the inside of your fuel cap."¹⁸

Even one car does not have one figure. Toyota's specifications page for the 2023 Corolla sold in the US lists the recommended cold pressures by the tyres fitted, four tyre types in all, on pp. 397 and 398: with 195/65R15 tyres, 33 psi (230 kPa) front and 30 psi (210 kPa) rear; with 205/55R16 tyres, 35 psi (240 kPa) front and 33 psi (230 kPa) rear; the two 18-inch types share the first pair.¹⁰ (psi is pounds per square inch; kPa, kilopascals, is the metric unit, and 100 kPa is 1 bar.) So "which car" includes which tyres. Lesson 7, "Tyres I: pressure, the placard and TPMS", teaches the check itself.

A figure that travelled too far

Numbers also escape from the car they belong to and turn into rules for everyone. CalRecycle, California's waste and recycling agency, runs a campaign against one: "The old standard of 3,000 miles is out of date and no longer applies to most cars." It then gives a spread rather than a number, saying many cars "can be driven up to 5,000, 7,500, 10,000, and even 15,000 miles", sends people to their owner's manual, and adds that "CalRecycle does not make recommendations regarding oil change frequency for any specific make or model of vehicle".¹⁷ Even the spread is for many cars, not yours, and yours is the one in your handbook.

Two cars and their handbooks

First, the simple case. The owner of a 2023 Corolla sold in the US starts a car file (the course project, a folder for one car). She opens the handbook's emergency section and the specifications and writes down four things, with page numbers:

• The jack's warnings, p. 372, including "Do not put any part of your body under the vehicle while it is supported by the jack."
• The wheel-nut torque, pp. 376 and 377, and the compact spare's speed limit, p. 378.
• The cold pressures, p. 397. She reads the size on her tyres' sidewalls, 205/55R16, so her row is 35 psi front and 33 psi rear, and she checks that the placard on the door pillar agrees.¹⁰

Nothing there is hard. What makes it useful is that every figure has a page number next to it, so on a dark roadside she is not relying on memory or a search engine.

Now the wrinkle. Two friends compare notes after each has had a puncture. One drives a 2024 Civic, whose handbook says 80 lbf·ft (108 N·m). The other drives a Mazda3, whose handbook gives a range of 108 to 147 N·m. A forum post says "always 110". Which is right?

Each handbook, for its own car. The forum's figure is for nobody's. It happens to sit inside Mazda's range and just above Honda's figure, and on this course's reading that is a coincidence, not a confirmation. Mazda's handbook itself says what to do when you're unsure: "If you are unsure of how tight the nuts should be, have them inspected at an expert repairer".¹¹¹²

What a test certificate tells you

This is general information, not legal advice.

The reason is in how the test works. DVSA's manual tells its testers: "The MOT test must be carried out without dismantling, so it is not always possible to inspect some testable items."¹⁶ An MOT is a record of what a tester could see on one day. The duty to keep the car safe runs every time it's used, and lesson 20, "The law on a car's condition: Great Britain and Northern Ireland", sets out that law.

In the US there is no national test like the MOT. Whether a car is inspected at all is a state matter. The most recent official national count this course found is the Government Accountability Office's: 16 states with periodic inspection as of July 2015, and fewer since.²¹ Lesson 22, "The US: state inspections, emissions tests and tread law", works through five states' rules, including two with no periodic safety inspection for private cars.

Law, handbook or advice: whose, and for which car?

This is general information, not legal advice.

Home Repair and Maintenance asked three questions of every rule: law or advice, whose, and where? A car adds a third kind of rule, the handbook, and a second kind of where, which car. Car advice goes wrong one way more than any other: one car's figure, or one organisation's advice, repeated as if it bound every car everywhere. You've met three already: "always 110", "every 3,000 miles", and the number on the tyre.

So every rule in this course carries, in the sentence:

• Who says it. A law, a regulator, the Highway Code, a maker's handbook for its own car, a motoring organisation, a trade body or a charity.
• Whether it is law, the handbook or advice.
• Which car and which place it covers.

The Highway Code's two voices

The Highway Code is both law and advice, and it tells you which is which. Its introduction: "Many of the rules in the Code are legal requirements, and if you disobey these rules you are committing a criminal offence." Those rules "are identified by the use of the words 'MUST/MUST NOT'". The rest are advice, but the Code "may be used in evidence in any court proceedings under the Traffic Acts" to establish liability, and "This includes rules which use advisory wording such as 'should/should not' or 'do/do not'."⁵ Northern Ireland's Code, by its own introduction, uses the same two voices.⁷

Annex 6's paragraph on tyres has both voices a few lines apart. "Tyres MUST be correctly inflated" is law in Great Britain. "Tyre pressures. Check weekly. Do this before your journey, when tyres are cold." is advice.⁶ NHTSA, for the US, advises checking "at least once a month" when the tyres are cold, and TyreSafe, the industry-backed charity, says "every month or before every long journey".³¹⁸ Three bodies, two intervals, and the one legal rule among them, Great Britain's, sets no interval. It requires a pressure fit for the use, which the Code reads as the maker's figure.

Three labels for every job

Every job this course names carries one of three labels, in the prose:

• Yours. The sources put it in any owner's hands: checking tyre pressures and tread, reading the dipstick, topping up screenwash, walking round the lights, checking for recalls.
• Yours, on conditions. Allowed if a named condition is met, and the lesson names it: topping up coolant only when the engine is cold, with the handbook's coolant (this course's condition); a jump start, or a wheel change, only on the conditions lessons 13 and 19 set, and never on a motorway.
• Call someone. The law reserves it, the handbook says the owner must not, or every source this course read advises against it: anything on the high-voltage system, a brake-fluid level that keeps falling, any repair on a motorway.

Where the law allows more than the advice does, both go in, law first, and the label follows the advice. Tyre tread is the first case you'll meet. In Great Britain cars "MUST have a tread depth of at least 1.6 mm across the central three-quarters of the breadth of the tread and around the entire circumference".⁶ TyreSafe, backed by tyre makers, carmakers and retailers, says "Tyre and safety experts recommend replacing tyres at 3mm".¹⁸ Lesson 8, "Tyres II: tread, damage, age, and when to replace", sets out that argument, and Logic and Argument lesson 7, "Reconstruction and charity: the strongest version first", is the rule this course uses to hear both sides.

Cars that aren't yours

Many people drive a car they do not own outright: on a lease, on finance, from an employer, from a hire company, or borrowed. This course read no lease, finance or hire agreement, so its line here is its own: the agreement and the company decide who arranges servicing, tyres, repairs and recall work. Tell them in writing, and do only the owner's checks without asking. Every exercise that touches a car says "if it's yours, or its keeper agrees".

UK and US words

This course is written in British English and teaches both countries. At first use in each lesson it gives both words, and in quotations it keeps the source's.

Units come in pairs too: tread in millimetres (mm) and 32nds of an inch, pressure in psi with bar or kPa, torque in N·m and lbf·ft, speed in km/h and mph, temperature in °C and °F.

What this course leaves out, and why

The course teaches the checks, topping up screenwash, oil, and coolant (cold), reading warning lights, jump-starting by the handbook, and changing a wheel where it is safe and the handbook gives the method. It does not teach, anywhere, getting under the car, axle stands, changing oil, brake pads, filters or fuses, bulbs behind panels, plugging a tyre, forcing a diesel's filter to clean itself, reading fault codes, or anything on the high-voltage system.

That's this course's scope decision, not a claim that the work is unlawful. A page can't check a jack's footing, a torque, or a technician's training. Where a source gives a step the course does not teach, the course reports it as the source's and stops. Toyota's handbook, for one, says "Use a jack stand if it is necessary to get under the vehicle."¹⁰ That's Toyota's step, and this course stops short of it.

Driving is not taught anywhere on the institute's map. Whether to buy a petrol, diesel, hybrid or electric car is an argument this course takes no side in. Motorcycles, vans over 3.5 tonnes, towing and caravans weren't researched and aren't taught.

What people get wrong

"It passed its MOT, so it's fine." The MOT is done without dismantling, on one day, and GOV.UK says a car "can be unsafe even if you have a current MOT certificate".⁴¹⁶

"The AA (or AAA) says so, so it's official." The AA, the RAC and Green Flag sell breakdown cover and repairs, and AAA clubs sell roadside assistance and run a repair network, so this course labels them every time it cites them. None is a regulator. Their advice can be good, and it's still advice from a business, not the law and not your handbook.

"The number on a website applies to my car." Four handbooks, three different torque figures; one car, two sets of pressures depending on the tyres. The website does not know which car you have.

"Inflate to the number on the tyre." That's the tyre's maximum (FMVSS 139). The carmaker's figure is on the door pillar, the fuel flap or in the handbook.³⁹¹⁸

For your plan

The course project is a car file for one car. This lesson adds its first page: where the handbook is (or its web address), the ten figures with page numbers, and one line naming where you drive, so you know whose law and whose roadside advice applies (Great Britain, Northern Ireland, or your US state).

Connections

This course borrows its shape from Home Repair and Maintenance lesson 1, "How a house works, and where it switches off", whose three labels and "law or advice, whose, and where?" become the labels and the question here. Next, lesson 2, "The engine: petrol, diesel, and the drive to the wheels", opens the first box on the map and explains why an engine needs the oil and coolant you'll be checking. Car loans and insurance belong to Personal Finance Fundamentals lessons 3 and 8, "How debt really works" and "Handing off what you cannot absorb". Casualty care at the roadside belongs to First Aid and CPR, starting from its lesson 2, "Danger, the call, and recognising cardiac arrest".

Go deeper

• Your own handbook. The sources this course read send you there first. If it's lost, the maker's website is the place to look, as BAR says.
• The Highway Code, Annex 6, "Vehicle maintenance, safety and security", free, for Great Britain: two pages that mix MUST rules and advice, good practice for telling them apart.
• NHTSA, "Tires", free: the US federal regulator on pressure, the placard and the date code. This course read it from an archived copy.
• Tom Denton and Hayley Pells, Automobile Mechanical and Electrical Systems, 3rd edition (Routledge, 2023). A UK textbook for people training in car maintenance. This course read only its contents page, whose parts on engine, electrical, chassis and transmission systems share the core of the map in this lesson; the book itself wasn't read.

Sources

1. California Bureau of Automotive Repair, "Maintenance and repairs". Read: full page text, re-read 26 September 2026. No date shown.
2. fueleconomy.gov (US Department of Energy and EPA), "Tips for Hybrids, Plug-in Hybrids, and Electric Vehicles". Read: full body text, re-read 26 September 2026.
3. NHTSA, "Tires". Read: full page, from Internet Archive capture 20260924154655 (nhtsa.gov refuses automated readers); the live page is linked.
4. GOV.UK (DVSA), "Check your vehicle is safe to drive". Read: full text, re-read 26 September 2026; page updated 5 April 2018. Great Britain.
5. The Highway Code, "Introduction". Read: full text, re-read 26 September 2026; updated 1 July 2022. England, Scotland and Wales.
6. The Highway Code, "Annex 6. Vehicle maintenance, safety and security". Read: full text, re-read 26 September 2026; updated 29 January 2022. England, Scotland and Wales.
7. nidirect, "The Highway Code" (contents) and "Introduction to the Highway Code". Read: main text of both, 26 September 2026. Northern Ireland. Its breakdown and motorway rules were not read.
8. 49 CFR 571.110, FMVSS No. 110, "Tire selection and rims". Read: full section text, eCFR, re-read 26 September 2026 (version of 24 September 2026). US federal law.
9. 49 CFR 571.139, FMVSS No. 139, "New pneumatic radial tires for light vehicles". Read: S1 to S5.5; test procedures skimmed; the S3 definitions and S5.5 re-read 26 September 2026. US federal law.
10. Toyota, 2023 Corolla Owner's Manual, OM02568U, US market. Read: pp. 46, 350 to 353 and 370 to 386 at Stage 1; pp. 372, 376 to 378, 397 and 398 re-read on 26 September 2026.
11. Honda, 2024 Civic Sedan Owner's Manual, "If a Tire Goes Flat", US market, online. Read: full section text, re-read 26 September 2026.
12. Mazda, Mazda3 Owner's Manual, European English edition 8GD7-EE-17H, chapter "Flat Tyre". Read: all nine Flat Tyre pages at Stage 1; the temporary spare and wheel-nut pages re-read 26 September 2026.
13. Nissan (UK), 2023 LEAF online owner's manual, "Installing spare tyre" and "Temporary use spare wheel/tyre". Read: main text of each, re-read 26 September 2026.
14. Nissan, 2024 LEAF Owner's Manual, US market. Read: EV-7 to EV-8, CH-2, CH-12, 2-15 to 2-23, 6-10 to 6-12, 8-2, 8-5 to 8-8 and 9-3 to 9-4 at Stage 1; p. EV-8 re-read 26 September 2026.
15. Ford, 2024 Maverick Owner's Manual, edition 202307, USA and Canada, read from Internet Archive capture 20250505042038 of Ford's PDF. Read at Stage 1: pp. 89, 90, 113, 114, 164, 184, 193, 283 to 286, 308 and 309; p. 309 re-read 26 September 2026.
16. DVSA, MOT inspection manual: cars and passenger vehicles, "Introduction". Read: the Introduction in full, re-read 26 September 2026; manual updated 1 June 2026. England, Scotland and Wales.
17. CalRecycle, "Check Your Number, Because 3,000 Miles May Be Too Early to Change Your Oil", and nidirect, "The MOT certificate". Read: full text of each, re-read 26 September 2026. California; Northern Ireland.
18. TyreSafe, "Check your pressures" and "Checking Tyre Tread Depth". Read: full text of each, re-read 26 September 2026; both last updated 16 September 2026. A UK tyre safety charity backed by tyre makers, carmakers and retailers.
19. AAA, "How Often Should You Change Your Oil?". Read: full article text, re-read 26 September 2026. A US motoring club that sells roadside assistance and runs a repair network.
20. The textbooks' publisher pages: Halderman and Ward, Automotive Technology: Principles, Diagnosis, and Service, 7th edition (Pearson, 2025); Erjavec and Thompson, Automotive Technology: A Systems Approach, 7th edition (Cengage, 2020); Denton and Pells, Automobile Mechanical and Electrical Systems, 3rd edition (Routledge, 2023). Read: the full tables of contents of the first two and the top-level contents of the third; none of the books was read.
21. US Government Accountability Office, Vehicle Safety Inspections: Improved DOT Communication Could Better Inform State Programs, GAO-15-705, August
    2015. Read: full text, from the PDF copy on the Vermont legislature's website; the count of states re-read 26 September 2026 from Internet Archive capture 20260109053421 of gao.gov's PDF.
22. The Road Vehicles (Construction and Use) Regulations 1986, reg 27 and the Road Vehicles Lighting Regulations 1989, reg 23, legislation.gov.uk. Read: each regulation in full, 26 September 2026. Great Britain.