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A Field Guide to Dashboard Warning Lights

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A new symbol on the dashboard rarely shows up at a good moment. It tends to appear on the highway, after dark, with the next exit eight miles away. You don't need to recognise every icon to make the right call, though, because carmakers use colour the same way traffic lights do. Red means stop safely and soon. Amber or yellow means get it checked. Green and blue are just telling you something is switched on.

The guide below covers the lights most drivers will meet, grouped by colour. Symbols vary a little between brands, and your owner's manual has the definitive list for your car.

Red lights

  • Oil can (oil pressure). Of all the lights on the dash, this is the one that can turn a cheap problem into a new engine. It means oil pressure has dropped, and an engine running without pressure can be wrecked within minutes. Pull over, switch off and check the dipstick. If the level looks normal and the light comes back when you restart, call for a tow.
  • Thermometer in wavy lines (engine temperature). The engine is overheating. A counterintuitive trick buys you time: switch off the air conditioning and turn the heater up to full. The heater core works like a second radiator and pulls heat out of the engine, at the cost of a very warm cabin. Stop as soon as you safely can, and leave the radiator cap alone until everything has cooled, because the coolant is under pressure and can scald.
  • BRAKE, or an exclamation mark in a circle. Often nothing more than a parking brake that isn't fully released. If the brake is off and the light stays on, the brake fluid may be low or there may be a leak. That isn't something to test on the drive home.
  • Battery symbol (charging system). Despite the picture, it usually means the alternator or its drive belt has stopped charging, so the car is running on whatever is left in the battery. This is the one red light you can usually drive on, briefly. Turn off the stereo, heated seats and anything else you can spare, and drive straight to a garage rather than home.
  • Seated figure with a circle (airbag). A fault in the airbag system. The car drives normally, but the airbags may not deploy in a crash. Get it looked at promptly. Depending on the make, this light may be red or amber.
  • Steering wheel with an exclamation mark (power steering). On cars with electric power steering, this warns of a fault in the system. Steering will still work but may suddenly become very heavy, so drive gently to a garage. Some brands show it in amber.

Amber and yellow lights

  • Engine outline (check engine). This covers hundreds of possible faults, from a fuel cap that didn't click shut to a failing catalytic converter. A steady light means the car is safe to drive but needs a diagnosis. A flashing light is the exception to the colour rule: it signals a misfire bad enough to overheat the catalytic converter, so slow down and treat it as red.
  • Horseshoe with an exclamation mark (tire pressure). The tire pressure monitoring system, standard on US cars since the 2008 model year. It comes on when a tire is roughly 25 percent under its recommended pressure, which you can't reliably spot by eye. Cold mornings often set it off because air contracts, so check the pressures with a gauge before assuming a puncture. The correct figures are on a sticker in the driver's door jamb.
  • ABS in a circle (anti-lock brakes). Your normal brakes still work, but the anti-lock system won't step in during an emergency stop. Leave more space and get it checked. A faulty wheel-speed sensor is a common cause.
  • Skidding car (stability or traction control). A brief flicker on a slippery road means the system is working. A light that stays on means it has switched off or has a fault, often the same wheel-speed sensor behind the ABS light.
  • Coil-shaped symbol (diesel glow plugs). On diesels, wait for this to go out before starting the engine in cold weather. If it flashes while driving, the engine has a fault that needs checking.
  • Fuel pump. Low fuel. Most cars have a reserve of somewhere around 30 to 50 miles when it first comes on, but the figure varies widely by model, and running very low is hard on the fuel pump.
  • Wrench or spanner (service due). A maintenance reminder, not a fault. Book the scheduled service.

Green and blue lights

These confirm that something is on: headlights, fog lights, cruise control, a turn signal, or an eco or hybrid driving mode. The one blue light worth knowing is the high-beam indicator, which other drivers will remind you about if you forget it.

Two habits that save money

Watch the dash for a second when you start the car. Most warning lights flash on briefly as a self-test. If one that normally appears stays dark, its bulb or circuit has failed, and you would never get that warning when it mattered.

When the check engine light comes on, get the code read before anyone starts replacing parts. Many auto parts stores will read it at no charge, and a basic OBD-II reader costs about $20 and plugs into every car sold in the US since the 1996 model year. Write the code down before it is cleared, so the next mechanic can see what the car reported.