Practical car guides. Know what’s wrong and what to do next.
Amara Musa is a light-vehicle technician, technical manager and periodic vehicle inspection controller, with over 20 years of hands-on workshop experience and experience running a workshop. Trained in Norway, with EV training and basic and advanced diagnostics training.
Last reviewed 14 September 2026.
Quick answers
The colour of the light tells you how urgent it is: red means stop as soon as it is safe, amber means book a service, and grey is for information.
Pull over and turn the engine off as soon as it is safe. Without adequate oil pressure the moving parts inside the engine are not being lubricated, and the damage can happen within minutes.
The engine is overheating. Turn the air conditioning off, turn the heater on full, and pull over and switch off as soon as it is safe.
The charging system, usually the alternator, is no longer keeping the battery charged. Cut your electrical use and drive only as far as you need to reach a safe place or a repair shop.
First check that the parking brake is fully released. If the light stays on, or the pedal feels different from usual, stop driving.
The car drives normally, but the airbags and belt tensioners may be out of action. This is a safety fault and it should be put right promptly.
A flashing check engine light commonly means a severe misfire that is sending raw fuel into the exhaust.
If the check engine light is steady, it's usually safe to keep driving normally in the short term, but get the code read soon.
Your ordinary brakes will usually still work, but you may lose ABS assistance under hard braking.
If the light flickers while you drive, the traction control is working right now, and that is normal.
The car can usually still be steered, but the effort can rise significantly, especially at low speeds like parking.
One or more tires has fallen outside the recommended pressure range. Check the pressures against the sticker in the doorjamb, not against the number moulded into the tire.
The pads are approaching minimum thickness. The car still brakes, but book a service before the pads wear down the discs as well.
Check that the fuel cap is tightened fully and is not cracked. A loose, cracked or missing cap is one of the most common reasons for this light, and it is not a safety concern for driving.
A headlight, taillight or signal bulb has burned out and should be replaced. It is not an emergency, but a dead bulb makes you harder for other drivers to see, especially at night.
This is a reminder about scheduled maintenance, not a warning about a fault. The car has reached an interval in time or distance.
The reservoir is nearly empty. Top it up, and use a freeze-rated fluid in cold weather. An empty or frozen bottle in winter road spray makes it impossible to see.
The outside temperature is approaching freezing, and the road can be icy even when it looks dry.
Start with what you notice. Each symptom has its own page with a short answer, whether you can keep driving, and what to do now.
What you hear when you try to start narrows it down. A slow crank, or a click with no crank, points at the battery, the starter or a connection, and the battery terminals are the first thing to look at.
A battery that keeps going flat is either near the end of its life or not being recharged properly.
The alternator keeps the battery charged while you drive. When it fails, the car runs on battery power alone until the battery is drained.
A weak battery and a failing alternator can produce similar symptoms, a slow crank or a dead car, which is why a shop tests both rather than guessing.
If the engine stops while you are moving, the steering gets heavier and the brake pedal needs more force, but the car can still be steered and stopped.
A misfire means one or more cylinders is not burning its fuel properly. If the check engine light is steady, get the code read soon.
A rough or unstable idle is one of the least specific symptoms a car can produce. A vacuum leak, an ignition fault, injector imbalance, low compression, excess EGR flow, a contaminated throttle body and a sensor feeding incorrect data can all feel exactly the same.
A soft or spongy pedal can indicate air or moisture in the brake fluid, and it is one of the two brake symptoms to treat as urgent.
A consistent high-pitched squeal every time you brake is usually the pad wear indicator, a small metal tab designed to make that noise once the pads are thin.
If it only shakes when you brake, the cause is almost always in the brakes themselves, and most often in the rotors.
When and where you feel the shake narrows it down. A vibration or shimmy in the steering wheel is most often tire balance, though worn suspension or steering parts can cause it too.
A clunk or knock over bumps, especially at low speed, most often comes from worn bushings, sway bar links or a loose component, and it means get it checked soon.
A humming or growling noise that changes with vehicle speed is the classic sign of a wearing wheel bearing.
A squealing noise on startup is one of the signs a belt is due for inspection, along with visible cracking, fraying or a glazed surface.
When the click happens tells you where to look. A click when you try to start, with no crank, points at the battery, the starter or a connection.
Check the tire pressure first. It is the simplest cause to rule out, and one you can put right yourself.
When the car is moving too slowly for airflow alone, such as at idle or in traffic, the cooling fan has to pull air through the radiator.
You shouldn't keep driving. If the temperature gauge climbs into the red zone or the warning light comes on, pull over and let the engine cool before continuing.
Coolant should not disappear on its own, so a dropping level usually means a leak somewhere in the system.
The cabin heater borrows its heat from the engine, so a heater blowing cool air is often a cooling system clue.
An engine should not use a meaningful amount of oil between changes, so a level that keeps dropping is worth investigating.
The color narrows it down fast. Blue or blue-grey smoke means oil is being burned. Black smoke usually means the engine is running rich, burning more fuel than it should.
A turbo engine that feels flat is more often a boost leak or a boost-control fault than a failed turbocharger.
If engine speed rises without matching acceleration after the clutch pedal is fully released, especially in a high gear, uphill or under heavy load, the clutch is slipping.
On a manual car, which gears resist tells you where to look. Grinding into every gear, or trouble selecting first or reverse at a standstill, points at clutch drag: the clutch is not fully letting go.
A code points you toward a system, not to a part that needs replacing.
The control unit has detected a misfire in one or more cylinders without being able to tie it to a specific one.
The same fault as P0300, but the car has isolated it to one cylinder. The number in the code tells you which.
The engine is getting too much air relative to fuel. Usually safe to drive in the short term, but have it checked soon.
The catalytic converter is not reducing emissions as effectively as expected, judged by comparing the oxygen sensors before and after it.
The system that controls idle speed is not behaving as expected. Have it checked soon, especially if the engine sometimes stalls at idle.
This is a general code. It means the transmission control unit has found a problem and stored more specific codes of its own.
The system that captures fuel vapour has a leak. By far the most common cause is a loose, cracked or missing fuel cap.
The EGR system is passing less exhaust gas than expected. Not urgent for safety, but have it checked.
The engine is taking longer than expected to reach normal operating temperature, usually because the thermostat is stuck open.
The heater that brings the oxygen sensor quickly up to operating temperature is not working as it should.
Most of these take a few minutes once a month, on a cold engine and level ground, and can catch a slow leak long before it becomes a bigger problem. Uneven tire wear is often the first visible clue of a steering or suspension issue.
Check it once a month, with the engine switched off and cold and the car on level ground. It takes under a minute.
Once a month, with the engine off and the car on level ground, look at the brake fluid reservoir and read the level against its min and max markings.
There is no fixed mileage. Pads and rotors are replaced by condition, because wear depends heavily on driving style, road conditions and climate, so they are inspected at every tire rotation or service.
Check all four tires, and the spare, once a month and before long trips, on cold tires before you set off.
Uneven or unusual tire wear is often the first visible clue of a steering or suspension issue.
Most manufacturers recommend changing brake fluid on a time-based interval, commonly every two to three years, regardless of mileage or how the fluid looks.
Go through the car in order: the paperwork, a cold start, a walkaround in daylight, then a test drive at both low and highway speed. Any car you are seriously considering is worth a pre-purchase inspection from an independent mechanic.
Get the VIN before you arrange to meet and run a vehicle history report. At the viewing, check that the name on the title matches the seller's ID, and that the VIN on the title matches the VIN on the dashboard and the door jamb sticker.
A cold start tells you more than a warm one. Several faults show themselves in the first minutes after a cold start and fade once the engine has warmed up, so a car that is already running when you arrive can hide them.
Walk around the car in daylight before you get in for a test drive. Check panel gaps and paint texture, look under the car for rust, fresh undercoating and fluid drips, then open the hood and check the oil, coolant, battery terminals, belts and hoses.
Start the car from cold if you can, then drive it at both low and highway speed. Listen for unusual noises while accelerating, braking and turning, feel for vibration or pulling to one side, and test the brakes firmly in a safe, controlled area.
A fair quote and a proper invoice are both written and itemized, with parts and labor on separate lines. One red flag is a question; several are a reason to walk.
A reasonable quote is written and itemized: parts and labor on separate lines, the part type named, labor shown as hours times the shop's rate, and any diagnostic fee disclosed before you approve anything.
Most overcharging follows a few recognizable patterns: work unrelated to why you brought the car in, a lump sum with no breakdown, pressure to approve extra work immediately, no written estimate, and a diagnostic fee nobody mentioned.
A proper invoice, not just an estimate, should show itemized parts with part numbers or descriptions, itemized labor with hours and rate, any diagnostic or shop fees clearly labeled, whether the parts are OEM, aftermarket or used, and the warranty terms for both parts and labor.
A fuel smell or a visible leak near a hot engine is a fire risk: stop. A misfire only under load can be the fuel supply as much as the ignition, and a code alone does not prove an injector has failed.
A fuel smell together with black smoke or a visible leak usually means the engine is running rich from a leaking or stuck-open injector, or fuel is escaping from a line or seal.
A restricted injector flows less fuel and atomizes it poorly, which typically shows as a lean misfire on that cylinder, worst when the engine is cold or at idle, and rough running.
A tired pump can hold pressure at idle and fall away when the engine asks for flow, so the typical sign is a misfire only under load.
A hard hot restart usually means fuel pressure is lost after shutdown, through a leaking injector tip, a leaking pressure regulator or the check valve in the pump.
Some direct injection engines build deposits on the back of the intake valves, because fuel no longer washes them.
The preheat light is not a fault: wait for it to go out before you start. The particulate filter burns itself clean at steady speed, and AdBlue has to be topped up before the level reaches zero.
This light is preheating, not a fault. Wait until it goes out before you start. If it flashes after the engine has started, that is a fault.
The filter needs to burn itself clean, and it can only do that at speed. Take a longer drive at a steady pace instead of parking the car.
Top the AdBlue up before the level reaches zero. If the tank runs completely dry, many cars refuse to restart, and by then topping up at the roadside does not help.
The car measures the pressure drop across the particulate filter and finds it is not cleaning as expected.
One or more glow plugs, or the circuit that controls them, is not responding as expected. You notice it as hard starting on cold mornings and rough running for the first few minutes.
A hybrid that will not go to READY very often has a flat 12-volt battery, not a failed hybrid battery. A slightly different brake pedal on a cold morning is normal.
A hybrid that will not go to READY very often has a flat or worn 12-volt battery, not a failed traction battery.
Less electric running than before, or the engine starting far more often on a route you know, can point at reduced capacity in the traction battery or a fault in how it charges.
When you lift off or brake gently, the electric motor works as a generator. Brake hard or come to a complete stop, and the ordinary brakes take over.
A hybrid is not a car with less maintenance. Some items last longer, some are additional, and the petrol engine still needs everything a petrol engine needs.
Winter range loss is mostly cabin heating drawn from the battery, not the cold itself. A red high-voltage warning means stop as safely as you can and call for help.
Stop as safely as you can, get out of the car, and call for help. Do not open the hood and do not try to diagnose it yourself.
The battery management system has found a fault in the cells or in their management. It does not mean the pack is worn out, but it should not wait: drive to a workshop, not out on a long trip, and do not rapid charge on the way.
The range is nearly used up, so head for a charger now. Below around 5 percent most cars cut power sharply to get you there, and in winter that happens sooner than you expect.
The traction battery is too hot, usually after rapid charging or hard driving. Let the car cool before you charge again, and charging and full power return on their own.
The car could not complete a charge, or stopped one it had started. Try a different cable and a different charge point before assuming the car is at fault.
An electric car still has an ordinary 12-volt battery, and that is often what is flat when the car will not wake up.
The car has limited its power deliberately to protect itself. This is usually not a fault, but a state that passes.
An electric car needs less routine maintenance than a petrol car, and less is the accurate word, not none.
Home charging is AC charging: a wallbox or a domestic socket feeds the car's own onboard charger, which converts the power for the battery.
DC rapid charging is normal, intended use. It slows down as the pack fills because the battery management system lowers the current to keep every cell below its voltage limit, and the last few percent wait for the weakest cells to balance.
An electric car loses range in winter mainly because the cabin heat has to come from the battery.
On a used electric car, battery state of health matters more than mileage, age and equipment put together, and few sellers quote it.
P0A80 means the traction battery has degraded past the manufacturer's threshold. It is not a sudden fault but ageing that has been going on for a long time.
Codes from P0A00 to P0A0F cover an electric car's motor, the inverter that drives it, and the cooling for both.
P0A94 means a fault in the DC-DC converter. That is the part that takes power down from the traction battery to keep the 12-volt battery topped up: the alternator's job on an electric car.
Guides for hydrogen cars.
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