Dashboard warning lights

A light comes on while you're driving. You have a few seconds to decide what it means and what to do, usually in traffic, often in the dark. Most people know that red is bad and amber is less bad, and that is a fair start. But the colours are not law everywhere, the same symbol can change colour as a fault gets worse, and a light that flashes can mean something more urgent than the same light glowing steadily. Your car's handbook has a page that settles all of it for your car, and this lesson ends with you copying it onto a card you keep in the car.

Several lights below end with "stop". Where you stop is the callout's business, and lesson 16, "When the car stops: where, who stands where, and the call", and lesson 17, "Motorways and fast roads: go left, the live lane, and the smart motorway question", teach it in full. Nothing in this lesson asks you to open anything hot or look under the car.

Three sections below state law: the rules on what colour a light must be, the US brake standard's start-up check, and what the MOT and New York's inspection do with lit lamps. Each carries this label in short; here it is in full. This is general information, not legal advice. The rules differ between England and Wales, Scotland, Northern Ireland and each US state, and they change.

Red, amber, green: where the code comes from

The colours come from an international standard, ISO 2575, whose current edition is from 2021. It is a standard for the symbols on a car's controls and lights, and clause 5 gives the colours their meanings. This course read the publisher's free sample, which has clauses 1 to 5 in full but not the annexes with the symbols themselves.¹ Clause 5.1 reads:

• "red: danger to persons or very serious damage to equipment, immediate or imminent;"
• "yellow or amber: caution, outside normal operating limits, vehicle system malfunction, damage to vehicle likely, or other condition which can produce hazard in the longer term;"
• "green: safe, normal operating condition (where blue or yellow is not required)."¹

Clause 5.2 adds that some colours go with particular lights: blue for main beam, and yellow or amber for, among other things, "failure of anti-lock brake system". Clause 5.4 says white "may be used where none of the above conditions applies."¹

Read the red definition again, slowly. It covers two different things: danger to people, and very serious damage to the car. A red light doesn't tell you which. And both are "immediate or imminent", which is the word that separates red from amber. Amber's list is about the longer term: a system not working, damage "likely", a hazard that builds.

The clause that surprises people is 5.5: "A given symbol may be shown in more than one of the colours specified in 5.1 in order to convey a change in the operating condition."¹ So, on this course's reading, the same picture can glow amber when something is starting to go wrong and red when it has got worse. You cannot learn a light by its symbol alone. You learn it by its symbol and its colour, from your handbook.

Where the colours are law, and where they aren't

This is general information, not legal advice.

A standard becomes binding when a regulation adopts it. Two regulations matter here, and they don't adopt the same amount.

UN Regulation 121 is the international rule on how a car's controls and warning lights are identified, used for approving cars in many countries. This course read a 2014 bilingual copy published by Japan's transport ministry, because the official copies would not download, so later amendments may be missing; and it did not read how the regulation applies to cars approved in Great Britain today.² Its paragraph 5.4.1 says: "Light of each tell-tale listed in Table 1 shall be of the colour shown in column 5 of this table." In that table the engine oil pressure, engine coolant temperature and electrical charging tell-tales are all red, and the engine malfunction light (the check-engine light) and the anti-lock brake light are yellow. A footnote on several symbols lets them "be shown in other colours than specified in column 5 in order to convey different meanings", following the colour code in paragraph 5 of the 2004 edition of ISO 2575, which this course did not read; the 2021 edition's clause 5.5, above, says the same kind of thing.²

FMVSS 101 is the US federal standard on controls and displays. Its S5.4.1 says: "The light of each telltale listed in Table 1 must be of the color specified for that telltale in column 6 of that table."³ Column 6 fixes brake system malfunction as red, and the anti-lock, stability control and low tyre (tire) pressure lights as yellow. For engine oil pressure, engine coolant temperature and electrical charge, the table gives a symbol and leaves the colour column blank.³ US federal law, where a car has an oil light, says how it may be marked (the symbol, or the word "Oil"), not what colour it must be.

Sources: ²³. The FMVSS 101 table was read from its official images; its note 4 says "Red may be red-orange."³

Look at the brake lining row. The warning that a car's brake pads are worn is yellow in UN Regulation 121 and red in FMVSS 101 (for cars covered by the US brake standard).²³ Same condition, two colours, both lawful where they apply. That is the plainest proof in this lesson that you can't carry one rulebook's colours into a car built to another's.

The US brake standard, FMVSS 135, adds a detail worth knowing. It lets a maker show several brake conditions (low fluid, the parking brake on, and others) on one common light, which must say "Brake". But where a maker gives the anti-lock system its own light, "the letters and background shall be of contrasting colors, one of which is yellow".⁴ So a separate ABS light is yellow by law in the US, and S5.5.5(d)(6) says the same of a separate regenerative-braking light.⁴ Nissan's 2024 LEAF shows how that looks on a real car: a red BRAKE light and a separate yellow brake system light for the regenerative and electric brakes, with different instructions for each.⁷

Lights at start-up

This is general information, not legal advice.

Switch on the ignition and most of the dashboard lights up at once. The Highway Code's Annex 6, whose advice applies in Great Britain, explains why and what to watch for: "When you turn the ignition key, warning lights will be illuminated but will go out when the engine starts (except the handbrake warning light). If they do not, or if they come on while you are driving, stop and investigate the problem, as you could have a serious fault."⁵ That is a should-kind of line, advice rather than a MUST.

The US brake standard requires the same kind of check for the brake light: it must come on when the ignition is switched to "on" before the engine runs, or at a single press of a test button, and it must "remain activated as long as the condition exists".⁴ Ford's 2024 Maverick handbook says the same of its check-engine light: it "illuminates when the ignition is on and the engine is off, this is normal operation."⁶ Nissan's 2024 LEAF handbook gives the reason to watch: "If any light does not come on or operate in a way other than described, it may indicate a burned-out bulb and/or a system malfunction."⁷

So the start-up light show is a test, and it is the lights' own test. A light that comes on and goes out is working. A light that doesn't come on at all may have failed, which matters because it can't warn you. A light that comes on and stays on is the one Annex 6 tells you to investigate.

The stop-now group

Four lights are treated as stop-now by at least one of the sources read here, a handbook or the RAC: oil pressure, coolant temperature, brake, and, in an electric car, the 12 V charge light. What each source says to do is below, with whose words they are and for which car. The RAC is a motoring organisation that sells breakdown cover and repairs; it is not an official body.

Why these four? The sources give their reasons light by light. The RAC's for oil: "If the oil is not lubricating the engine effectively it could lead to expensive or even irreparable engine damage, so it's important to act quickly."⁸ Its reason for temperature is in the table. For the brakes, lesson 6, "Brakes, steering and suspension", set out what the red light can mean and quoted three handbooks, all of which say driving on could be dangerous. For the LEAF's charge light, Nissan's reason is that "The DC/DC converter system may not be functioning properly".⁷ What the four share, on this course's reading, is that each warns of something that can fail fast and badly: the engine wrecking itself, or the car losing its brakes or its electrics. None of the sources read explains how oil protects an engine; the textbooks named in lesson 2's Go deeper are where that is.

Stopping is the driver's call and it's Yours: pull over where it is safe, and switch off. What happens next splits.

The oil. Checking the level once the engine is off, on level ground, by the handbook's method, is Yours; topping up is Yours, on conditions (the handbook's grade, level ground, engine off). The cause, whether a leak, a pump or something else, is Call someone. The RAC says so too: if the level is fine, "the oil pump may be faulty", and it advises calling for recovery if you have breakdown cover, "as driving any further could damage the engine."⁸

The temperature. Here the rule every source agrees on is about the cap. The Highway Code's advice for an engine that has overheated: "you should wait until it has cooled naturally. Only then remove the coolant filler cap and add water or other coolant."⁵ The RAC says the same in its own words: "Stop and wait until the engine has cooled off before checking the gauge on the side of the coolant tank".⁸ How long that takes is the handbook's figure, not a universal one; Ford's is Ford's. Topping up coolant is Yours, on conditions: only when it's cold, and only with the handbook's coolant. Finding out why it overheated is Call someone.

The brake light and the EV's charge light: Call someone, once you've stopped. Ford's first step for its brake light, making sure the parking brake is released, is the one innocent cause any handbook names, and lesson 6 covers it.

The charge light in a petrol or diesel car is the light lesson 5, "The 12 V battery: what it does, and why short trips flatten it", found the sources disagreeing about. The Highway Code's two sentences belong together. The first is the general one quoted above: a light that comes on while you're driving means "stop and investigate the problem, as you could have a serious fault". The next paragraph says: "If the charge warning light comes on while you are driving, it may mean that the battery isn't charging. This should also be checked as soon as possible to avoid loss of power to lights and other electrical systems."⁵ Ford says "Have your vehicle checked as soon as possible", and on its catalytic converter page, for the battery lamp among others, that continuing to drive "may cause reduced power or the engine to stop"; the RAC says "You should not drive if the battery warning light is on."⁶⁸ The handbook for your car decides.

The check-engine light: what it watches

The amber engine light has several names. The UK calls it the engine management light; the US, the check engine light; both are the malfunction indicator lamp, or MIL. It is a different kind of light from the stop-now four, and the difference is what it watches.

In the US it comes from emissions law, not the controls standard. EPA's 2003 fact sheet on on-board diagnostics (OBD) explains it. OBD "is additional computer software that monitors the emission control and emission-related components/systems, along with certain engine components". From that, "the on-board computer is able to determine the presence of a malfunction or deterioration that can affect emissions and illuminate the "Check Engine" or "Service Engine Soon" light".¹⁰ What the second-generation system watches includes "catalyst efficiency, oxygen sensor response and heater, exhaust gas re-circulation (EGR) system, fuel delivery system, engine misfire, evaporative system".¹⁰ The requirements "were implemented beginning with the 1994 model year", and because most makers got waivers for 1994 and 1995, "1996 is commonly identified as the first year of full implementation".¹⁰ This course did not read EPA's regulation itself, nor the European rules on when the same system was fitted to cars sold in the UK.

Two lines from the fact sheet explain why the light is easy to ignore. First: "In some instances, the computer software may identify a problem before there is an overt indication to the vehicle operator."¹⁰ The car can feel fine. fueleconomy.gov, run by the US energy department and EPA, says the same from the driver's side: "Modern vehicles are so advanced that they may seem to drive normally even when a repair is needed, which sometimes leads drivers to ignore the indicator."¹¹ Second: under the second-generation rules, the lamp "extinguishes after 3 consecutive trips where the problem did not re-occur."¹⁰ So a light that went out by itself has told you the problem hasn't come back for three trips. On this course's reading, that's not the same as telling you it was never there.

What does a steady light call for? fueleconomy.gov: "It could be something as minor as a loose gas cap, but it could also be a more serious issue that could reduce your fuel economy, increase emissions, and/or lead to costly repairs later. So, when the check engine light comes on, have your vehicle inspected by a mechanic."¹¹ The RAC, which sells breakdown cover and repairs: "While you can typically drive whilst your engine light is on, we'd strongly recommend getting a mechanic to look at your car as soon as possible." It goes on: "Continuing to drive with this light on will likely lead to further damage to the engine and the surrounding systems."⁹ Ford adds the warranty. On its catalytic converter page, beside the temperature, battery and engine lamps, it says: "Continuing to drive your vehicle may cause reduced power or the engine to stop. Failure to respond to a warning lamp may cause damage that your vehicle Warranty may not cover. Have your vehicle checked as soon as possible."⁶

None of those says "stop now". All of them say have it looked at, and Ford and the RAC say as soon as possible. A steady check-engine light is a booking, not a lay-by, and finding its cause is Call someone. This course does not teach reading fault codes with a scanner, for the reasons lesson 1, "What a car is made of, and why the handbook comes first", gave.

Steady or flashing

Ford's 2024 Maverick handbook gives the distinction that matters, on page 164:

• Steady: "If it illuminates when the engine is running, the on-board diagnostics system is detecting a malfunction of the vehicle emission control system."
• Flashing: "If it flashes, engine misfire could be occurring. Increased exhaust gas temperatures could damage the catalytic converter or other vehicle components. Avoid heavy acceleration and deceleration, and have your vehicle checked as soon as possible."⁶

That's the mechanism as far as Ford gives it: a misfire could be occurring, and the raised exhaust temperatures that come with it could damage the catalytic converter, which the RAC (it sells breakdown cover and repairs) describes as controlling the emissions that come from the car.⁶⁹ Ford doesn't explain the misfire itself further, and nor does this course. Page 114 of the same handbook says it more shortly: "If it flashes, have your vehicle checked immediately."⁶ The RAC, for the UK: "If the light is flashing then this suggests a more serious issue and you should get have the vehicle inspected by a qualified professional" (the grammar is the RAC's).⁹

You may read online that a flashing light means the car could catch fire. No source this course read says so, and so this course does not.

A climb out of the town of Durango

Now a case with a gap for you. A 2024 Ford Maverick with the petrol (gasoline) engine is on a long climb out of Durango, towing nothing, with 40 miles (about 64 km) to go to where the driver is staying. The check-engine light starts to flash, and the engine feels rough under load.

Work it out from Ford's two pages before you open the answer. What does the driver do in the next minute, and what does he do about the 40 miles?

Amber lights that aren't stop-now

Most of the amber lights ask for a booking, not a stop. The ones you're likeliest to meet:

ABS. Ford: "Your vehicle continues to have normal braking without the anti-lock brake system function. Have your vehicle checked as soon as possible."⁶ Nissan's LEAF handbook says the same in its own words: the brakes work normally but without the anti-lock assistance.⁷ What you've lost is what lesson 6 described, the ABS's help in keeping steering control under hard braking. That is why it's amber. ISO 2575 names "failure of anti-lock brake system" as an amber case, and on its definitions this is a system not working, with the normal brakes still there, not danger "immediate or imminent".¹ A red brake light, on this course's reading, can mean the brakes themselves are affected. The RAC, which sells breakdown cover and repairs, adds the combination that changes things: if the ABS light "comes on with the brake warning light, it could indicate that the brake system is failing and you should stop straight away and call for recovery if you have breakdown cover."⁸ Amber alone, book it in; amber with red, stop.

Airbag. Nissan: "If the supplemental air bag warning light is on, it could mean that the front air bag, side air bag, curtain air bag and/or pretensioner systems will not operate in an accident."⁷ Nothing about the airbags is an owner's job, so this is Call someone, and never a reason to disable anything.

Tyre pressure. Lesson 7, "Tyres I: pressure, the placard and TPMS", covers what the light is required to do and why it comes on so late. On a steady light, check the tyres with a gauge; a light that flashes and then stays on is a fault in the system itself.

Stability control (ESC). The RAC (breakdown cover and repairs) says a flashing light means the system is intervening, for example on a slippery road, a light that stays on means it isn't working properly, and one with "OFF" means it has been switched off.⁸ But makers use different symbols and names, and even the MOT manual tells testers they "might need to check the owner's handbook" to be sure what theirs means.¹² So should you.

Diesel particulate filter and AdBlue. Lesson 3, "Diesel exhaust: the DPF and AdBlue", covers both lights and what each asks of you, including why an AdBlue top-up is Yours, on conditions.

Glow plugs, on a diesel. Lesson 2, "The engine: petrol, diesel, and the drive to the wheels", covers the glow-plug light at starting: wait for it to go out. If it stays on once the engine is running, DENSO, the glow-plug maker quoted there, says it "should not be ignored". DENSO puts the likeliest causes in the glow plugs or the sensors that control them, and adds that it "could also indicate a problem with the engine itself". In the worst case, it says, the engine or the DPF can be damaged, so the cause should be found at once.¹⁴ No handbook this course read gives the step, so copy your handbook's onto your card, and the cause is Call someone.

The RAC's table, and why the handbook still governs

The RAC, which sells breakdown cover and repairs, opens its guide to warning lights with the rule most people carry in their heads, as a table:

Source: ⁸.

It is a useful rule of thumb and it's where most people start. But read the rest of the same page and the RAC softens its own red row. For the temperature light, as you saw, it gives a route by which you "should be fine to continue your journey".⁸ For its brake light it says to stop and, "Unless you know how to check your brake fluid levels yourself", get to a garage, and to call for recovery if you have breakdown cover.⁸ The table is a summary; the page's own detail is more careful than the table.

Two other things are worth saying, neither as a criticism. The RAC sells breakdown cover and mobile mechanics, and its page says so beside the table; "call for recovery" is a service it offers. And its table is for every car, while the handbooks are for one. For the charge light, the RAC says don't drive, while Ford's handbook for its pickup says have it checked as soon as possible and warns the engine may stop, and lesson 5 set a third maker's handbook beside them that says stop.⁶⁸ When the general rule and your handbook disagree, the handbook is written by the people who know that car, and every source this course read sends you to it.

What the MOT and New York's inspection do with lit lamps

This is general information, not legal advice.

A warning lamp can also decide whether a car passes its periodic test. The two tests this course read on the point say this. Northern Ireland's test was not read on it.

In Great Britain, DVSA's MOT inspection manual, which applies in England, Scotland and Wales and was last updated on 1 June 2026, lists these as defects:¹²

• "Engine MIL inoperative or indicating a malfunction": Major. The tester switches on and checks that the lamp "illuminates and then goes off". It's checked on petrol cars (hybrids included) with up to 8 passenger seats first used on or after 1 July 2003, and on diesels first used on or after 1 July
  2008. Those are the test's dates, not the dates the system was fitted.
• "An SRS malfunction indicator lamp (MIL) indicates a system malfunction": Major. (SRS is the airbag system. A lamp showing that the passenger airbag has been switched off is "not to be regarded as a defect".)
• "ESC MIL indicates a system malfunction": Major.
• For ABS, "Warning device shows system malfunction": Major.
• "Brake fluid warning light illuminated or defective": Minor.

A Major defect fails the test; a car with only Minor defects passes, with them recorded. The manual says so in its introduction. Notice the last line: a lit brake fluid light is Minor on the test, while Nissan's handbook says to stop the car immediately, and lesson 6 showed all three handbooks it read calling driving on dangerous. Both can be true, because they answer different questions. The manual sorts what a tester sees on one day into pass and fail; the handbook tells a driver what to do on the road. Law first, advice second, and the label follows the advice: a lit red brake light while driving is Call someone, whatever the test would say.

In New York, the Department of Motor Vehicles' inspection page (read from an Internet Archive capture of June 2026) says most petrol vehicles from 1996 and diesels from 1997 with a gross vehicle weight rating under 8,501 pounds (about 3,856 kg) take an on-board diagnostics emissions inspection, and "This test examines the Malfunction Indicator Lamp (MIL), also known as the "check engine" light, for operation/illumination, and verifies the test results of the vehicle's "on-board emissions diagnostic" system." It advises: "If the vehicle's Malfunction Indicator Lamp (MIL, or "check engine" light) indicates there may be a malfunction or other problem, have the vehicle properly repaired."¹³ The same page treats the airbag lamp differently from the MOT: "Your vehicle's Air Bag Warning Lamp will be checked for proper operation. You will be informed if the vehicle's air bag warning lamp is on or is not working. This is an advisement only and not cause for rejection."¹³

Neither is right and the other wrong. They are two places' rules. US states differ: GAO, the US Congress's audit office, counted 16 with periodic safety inspection in 2015, fewer since, and emissions testing depends on where a car is registered.¹⁵ Lesson 22, "The US: state inspections, emissions tests and tread law", covers the rest.

What people get wrong

"The colours mean the same everywhere, by law." ISO's code is voluntary, UN Regulation 121 makes more of it law than the US standard does, and the brake-wear warning is yellow under one and red under the other.²³ Your handbook shows your car's colours.

"Lights at start-up mean something's wrong." They are the bulb check, and they're supposed to come on. The one to worry about is a light that stays on, or one that never comes on at all.⁵⁷

"A steady check-engine light can wait until the next service." Every source read says to have it looked at, the RAC, which sells breakdown cover and repairs, warns that driving on will likely do further damage, and Ford's handbook says that ignoring it can cost power, stop the engine, and cause damage its warranty "may not cover".⁶⁹¹¹

"Every red light means call recovery." It's a reasonable default, and it's the table of the RAC, which sells breakdown cover and repairs. But the handbook for the car governs, and the RAC's own page is more careful than its table.⁸

Practice

Now a sort. Eight lights, as a driver might describe them:

1. A red oil can, while driving.
2. A red thermometer in waves, while driving on a hot day.
3. An amber ABS light, alone, on a dry road.
4. The same amber ABS light, with the red brake light.
5. An amber engine outline, steady, and the car feels normal.
6. The same engine outline, flashing, and the engine judders.
7. A red battery symbol in an electric car, with the car in its ready-to-drive state.
8. Every light on the dashboard, for three seconds after you switch on, then all but the parking brake light go out.

For your plan

This lesson adds a warning-light card to your car file: the handbook's page numbers; for each of the stop-now lights, the symbol, the colour and the handbook's instruction in its own words; the check-engine light steady and flashing; ABS, airbag and tyre pressure; and a label beside each. Keep a copy in the glovebox, where you can read it in a lay-by.

Connections

Lesson 3, "Diesel exhaust: the DPF and AdBlue", covers the diesel lights. Lesson 5, "The 12 V battery: what it does, and why short trips flatten it", has the full disagreement over the charge light, lesson 6, "Brakes, steering and suspension", the red brake light, and lesson 7 the tyre pressure light. Lesson 9, "Under the bonnet: oil, coolant, brake fluid and screenwash", is where the course deals with checking the levels those lights are about. Lesson 21, "The MOT and Northern Ireland's vehicle test", covers the whole MOT, and lesson 22 the US emissions tests.

Go deeper

• Your own handbook, the warning-light pages. Every source in this lesson sends you there, and it's the only one that knows your car's symbols and colours.
• EPA, "On-Board Diagnostic (OBD) Regulations and Requirements: Questions and Answers", free, 2003. Read here: questions 1 to 8 in full. A short, plain account of what the check-engine light is watching and why it exists.
• DVSA, MOT inspection manual, section 8, "Nuisance", free. Read here in full. How a tester in Great Britain checks the engine light, with the dates.
• RAC, "Dashboard warning lights guide", free. Read here in full. A motoring organisation that sells breakdown cover and repairs; a readable tour of the common symbols, best read to the end rather than stopped at the table.

Sources

1. International Organization for Standardization, ISO 2575:2021, Road vehicles: Symbols for controls, indicators and tell-tales, ninth edition, free publisher sample (catalogue page: iso.org). A voluntary international standard. Read: the free sample only, clauses 1 to 5 in full, re-read 26 September 2026. The symbol annexes are not in the sample and were not read.
2. UNECE, Regulation No. 121: Uniform provisions concerning the approval of vehicles with regard to the location and identification of hand controls, tell-tales and indicators, bilingual English and Japanese copy published by Japan's Ministry of Land, Infrastructure, Transport and Tourism, PDF, created 23 March 2014. Read: paragraphs 5.1 to 5.5 and Table 1 in full; Table 1 re-read from the page image, 26 September 2026. This copy may predate later amendments; how the regulation applies to cars approved in Great Britain now was not read.
3. 49 CFR 571.101, Federal Motor Vehicle Safety Standard No. 101, "Controls and displays", US federal law, last amended 3 January 2025. Read: the full text through the eCFR API (version of 1 September 2026), and Table 1 and its notes from the five official images, 26 September 2026.
4. 49 CFR 571.135, Federal Motor Vehicle Safety Standard No. 135, "Light vehicle brake systems", US federal law. Read: S5.5 to S5.5.5 in full through the eCFR API (version of 1 September 2026), 26 September 2026.
5. The Highway Code (Department for Transport and DVSA), "Annex 6. Vehicle maintenance, safety and security", updated 29 January 2022. Great Britain. Read: full text, re-read 26 September 2026 through the GOV.UK content API. The lines used here are advice, not MUST rules.
6. Ford Motor Company, 2024 Maverick Owner's Manual, edition 202307, US and Canada, read from Internet Archive capture 20250505042038 (Ford's site refuses automated readers). Read in full at Stage 1: printed pages 89, 90, 113, 114, 164, 184, 193, 283 to 286, 308 and 309; pp. 113, 114, 164 and 183 re-read for this lesson, 26 September 2026. A maker's handbook for its own car, petrol or hybrid.
7. Nissan North America, 2024 LEAF Owner's Manual and Maintenance Information (US market), PDF. Read in full at Stage 1: 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, 9-3 to 9-4; pp. 2-15 to 2-20 re-read for this lesson, 26 September 2026. A maker's handbook for its own electric car.
8. RAC, "Dashboard warning lights guide: red, amber and green symbols explained", dated 18 August 2026. A motoring organisation that sells breakdown cover and repairs; not official. Read: full text, re-read 26 September 2026.
9. RAC, "Reasons your amber or orange engine management light (EML) is on", dated 11 August 2026. A motoring organisation, as above. Read: full text, re-read 26 September 2026.
10. US Environmental Protection Agency, "On-Board Diagnostic (OBD) Regulations and Requirements: Questions and Answers", EPA420-F-03-042, December 2003. US federal. Read: questions 1 to 8 in full (the rest skimmed), re-read 26 September 2026. EPA's OBD regulation itself was not read.
11. fueleconomy.gov (US Department of Energy and EPA), "Keeping Your Vehicle in Shape", undated. Read: full body text, re-read 26 September 2026.
12. Driver and Vehicle Standards Agency, "MOT inspection manual: cars and passenger vehicles", manual updated 1 June 2026. Applies in England, Scotland and Wales; written for testers. Read: the Introduction in full at Stage 1; sections 1, 7 and 8 in full through the GOV.UK content API, 26 September 2026.
13. New York State Department of Motor Vehicles, "New York State Vehicle Safety/Emissions Inspection Program", read from Internet Archive capture 20260610152208 (the state's site refuses automated readers, and the later capture 20260710141515 that Stage 1 read would not load on 26 September 2026). New York. Read: the page in full, 26 September 2026. The live page is linked.
14. DENSO Europe, "Why might the glow plug warning light come on?", dated 10 November 2023. A glow-plug maker writing about its own product; not official. Read: full article text, re-read 26 September 2026. Its "10 to 15 seconds" rule of thumb is not used here.
15. 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 (SOURCES, Stage 4 note, lesson 01). That fewer states inspect now rests on Texas, which ended safety inspection for non-commercial vehicles from 1 January 2025.