Colour tells you most of what you need to know. Carmakers use roughly the same system as a traffic light:
- Red: a problem that affects safety or can cause damage right away. Stop somewhere safe and deal with it before driving on.
- Amber or yellow: something needs attention soon. You can usually keep driving carefully, but book it in.
- Green or blue: information only. Headlights on, high beams on, cruise control set.
Symbols vary a little between makes, and some lights change colour depending on how serious the fault is. Your owner's manual has a page showing every symbol for your car. Find it before you need it.
The common ones
| Light | Colour | What it means | What to do |
|---|---|---|---|
| Oil can | Red | Oil pressure has dropped. The engine isn't being lubricated properly. | Pull over and shut the engine off. Check the oil level. If the level is fine, or the light stays on after topping up, have it towed. |
| Thermometer | Red | The engine is overheating. | Pull over and shut it off. Don't open the radiator cap while it's hot. Let it cool, check the coolant level and get it looked at before driving far. |
| Battery | Red | The charging system has stopped charging. The car is running on the battery alone. | Turn off the heater fan, seat heaters and radio, and drive straight to a shop or home if it's close. The car can stall once the battery runs down. |
| BRAKE, or an exclamation mark in a circle | Red | Parking brake on, brake fluid low, or a fault in the brake system. | Check the parking brake first. If it's off and the light stays on, stop and have the brakes checked before driving on. |
| Steering wheel | Red or amber | Fault in the power steering system. | Steering may get heavy, sometimes very heavy. Drive slowly to a safe spot and book it in. |
| Seated person with a circle | Red or amber, varies by make | Fault in the airbag system. Airbags may not deploy in a crash. | The car drives normally, but book it in soon. |
| Engine outline, steady | Amber | The engine computer has stored a fault code. Could be minor, could be the start of something bigger. | Make sure the gas cap is tight. Book a diagnostic soon. |
| Engine outline, flashing | Amber | A misfire bad enough to damage the catalytic converter. | Ease off, avoid hard acceleration and heavy loads, and get it in the same day. If the car is shaking badly or losing power, stop driving it. |
| ABS | Amber | The anti-lock system is off. Normal braking still works. | Brake gently on slippery roads and book it in. |
| Tire cross-section with an exclamation mark | Amber | One or more tires are low on pressure. | Check all four with a gauge and inflate to the door placard. If the light flashes for about a minute at startup and then stays on, the sensor system itself has a fault. |
| Car with wavy lines | Amber | Flashing: traction or stability control is working. Steady: the system is off or has a fault. | Flashing: ease off, the road is slippery. Steady: check you haven't switched it off, then book it in. |
The check-engine light in more detail
This is the light people ask about most. When it comes on steady, the engine computer has seen a reading outside its normal range and stored a trouble code. That could be a loose gas cap, a failing oxygen sensor, a small leak in the evaporative emissions system, or the early stage of something more serious. The car often drives normally, which is why people put it off.
Don't leave it for months. While the light is already on, a second fault won't give you a fresh warning. Small problems left long enough can also turn into larger ones, a misfire that eventually takes out a catalytic converter being the classic example.
A flashing check-engine light is a different situation. It usually means the engine is misfiring badly enough that unburned fuel is reaching the exhaust, where it can overheat and destroy the catalytic converter. Reduce the load on the engine, stay off the highway if you can, and get the car in that day.
A code is not a diagnosis
Some parts stores will read your code, and inexpensive plug-in readers do the same job. The code tells you which system reported a problem, not which part failed. P0171, for example, means the engine is running lean. That can be a vacuum leak, a dirty airflow sensor, a weak fuel pump or several other things. Proper diagnosis means testing until the actual cause is found, before anything gets replaced.
Lights that show up with the cold
The first cold mornings of fall turn on a lot of tire pressure lights. Pressure drops roughly 7 kPa (1 psi) for every 5 to 6 °C the temperature falls, so tires that were fine in September can be low in November. Check and adjust them cold, before driving. Weak batteries also show themselves in the cold, often as a slow crank before any light ever comes on.
If a light comes on and you're not sure how serious it is, call us at (647) 568-7110 and describe what you're seeing, including the colour and whether it's steady or flashing.
