The dashboard lights that mean stop the car now

Quick answer: A red light means get off the road and shut the engine off as soon as it's safe. An amber light means deal with it this week. A flashing check engine light counts as red.

It's 9:40 on a Sunday night, sixty miles from home, both kids asleep in the back. A little red oil can lights up on the dash. The car feels fine. It sounds fine. So you tell yourself you'll call the shop Monday.

That's the most expensive sentence in driving. An engine with no oil pressure can grind itself to scrap long before you see your exit. Monday will arrive with a tow bill and a quote for a new engine.

Most drivers know what a few of these symbols look like. Far fewer know which ones are emergencies. That second part is the one that matters.

The color is the system

Car makers mostly follow a traffic-light code, and once you know it you can read a light you've never seen before.

• Red: something is wrong that can hurt the car or you. Stop soon.
• Amber or yellow: something needs attention. Keep driving, carefully, and book it in.
• Green or blue: a system is on. High beams, cruise control, turn signals. Nothing's wrong.

One honest caveat. Symbols vary a little between brands, and newer cars often show a text message beside the icon. Read the words if you get them. Your owner's manual has a page with every light your specific car uses, and it beats any general guide, this one included.

The ones that mean right now

Oil pressure. An old-fashioned oil can, sometimes with a drip. This is the big one. It means oil isn't reaching the engine at the pressure it needs. Pull over, turn the engine off, and leave it off. Give it ten minutes, then check the dipstick. If the oil is low, top it up with the right grade and see whether the light clears. If the level is fine and the light stays on, don't drive it. Get a tow.

Engine temperature. A thermometer dipping into wavy lines, usually red. The engine is overheating. Get off the road and shut it down. Don't open the radiator cap on a hot engine. The coolant is under pressure and it can spray scalding fluid at your face. Wait until the engine is cool to the touch.

If you physically can't stop yet, say you're on a bridge or in a construction zone with no shoulder, turn the heater to full hot and the fan to high. It's miserable in July, but it pulls heat off the engine and buys you a little distance.

Brake system. A red circle with an exclamation mark, or the word BRAKE. Check the obvious first: is the parking brake partly on? Release it fully. If the light stays on, you may be low on brake fluid or have a hydraulic problem. Press the pedal gently. If it feels soft, sinks or travels farther than usual, stop and call for a tow. Brakes aren't the place to find out how much farther you can push it.

Charging system. A little battery shape. The alternator has stopped charging, and the car is now running on whatever's left in the battery. You've got some time, but it's limited. Kill everything you can: AC, radio, heated seats, phone chargers. Drive straight to a shop or somewhere safe, and don't turn the engine off until you get there, because it may not start again.

Watch the temperature gauge while you do this. On many cars the same belt that turns the alternator also drives the water pump. If the belt snapped, the engine will start to overheat as well, and then you're back to stopping now.

The flashing one people get wrong

A solid check engine light is amber territory. It could be something as small as a loose gas cap.

A flashing check engine light is different. It usually means the engine is misfiring badly enough to dump unburned fuel into the exhaust. That fuel can overheat the catalytic converter, which is one of the priciest parts on the car to replace. Slow down, take the next safe exit and get it looked at before you go much farther. Don't take a flashing light onto the interstate for another hour of driving.

The ones that give you a few days

Solid check engine. Tighten the gas cap until it clicks. It can take a few drives for the light to clear. If it doesn't, get the code read this week.

Tire pressure. A horseshoe shape with an exclamation mark in it. Check all four tires at the next gas station. The correct pressure is on the sticker inside the driver's door jamb, not the number on the tire sidewall. That one's the maximum the tire can hold, and it's the wrong target. Cold mornings drop tire pressure, so the light often shows up on the first frosty day of fall. If one tire is much lower than the others, look for a nail.

ABS. Your normal brakes still work. The anti-lock system doesn't, so a panic stop on a wet road won't behave the way you're used to. Leave more room and book it in.

Airbag. A seated figure with a circle in front of it, or the letters SRS. The car drives normally, which is why people ignore this one for months. The airbags may not deploy in a crash. If you carry children, this goes to the top of the list.

Traction or stability control. A car with squiggly tracks behind it. If it flickers on a slick road, the system is doing its job. If it stays on solid, the system is switched off or has a fault.

How to actually pull over

Stopping is a skill too, and most people have never practiced it.

• Signal early and get as far off the road as you can. An exit ramp, a gas station or a parking lot beats any shoulder.
• Hazards on.
• On a busy highway shoulder, get out on the side away from traffic, or stay put with your seatbelt on. Standing between your car and passing traffic is the most dangerous place you can be.
• Take a photo of the dash before you turn the car off. It helps the shop, and it helps you later when you're explaining what happened.
• If it's dark and the spot feels wrong, roadside assistance first, then your husband, your dad or a friend. Pride doesn't get you home.

Walk into the shop already knowing

Every car sold in the US since 1996 has a diagnostic port under the dashboard, usually near your left knee. A basic code reader plugs into it, many of them talk to an app on your phone, and you can find one for under thirty dollars. Big chain parts stores like AutoZone and O'Reilly will also read the code for free in their parking lot.

The reader gives you a code, something like P0420. Look it up. Now you're walking into the shop knowing what the car has already said, and you're a lot harder to upsell. If a shop tells you something unrelated to the code needs urgent work, ask them to show you. A good mechanic will happily walk you over to the car. One who won't has told you something useful too.

This isn't about distrusting mechanics. Find a good one and stay loyal. It's just that a customer who knows the basics gets treated like a customer who knows the basics.

A one-time setup worth an afternoon

Do this once and you're ahead of most drivers on the road:

• Find the warning light page in your owner's manual and photograph it, so you have it even if the manual goes missing.
• Keep a quart of the exact oil your car takes in the trunk. The grade, something like 0W-20, is printed in the manual and often on the oil cap.
• Add a jug of premixed coolant and a cheap tire gauge.
• Plug in the code reader once while everything's fine, so you're not learning the app on a dark shoulder.
• Teach your teenager the colors before they get their license. Five minutes in the driveway.

And if a light comes on while you're driving someone else's car, tell them the same day. Don't hand it back with the light glowing and say nothing. Call them, get it sorted, and return it with a full tank.

Stopping for thirty seconds costs you nothing. Driving thirty more miles can cost you the engine.