What Does the 'Service Engine Soon' Light Mean?

What Does the 'Service Engine Soon' Light Mean?
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Modern cars use complicated onboard computers that constantly assess engine conditions and illuminate warning indicators when issues come up or maintenance is required. One of the most common warning lights is the “service engine soon” light. While firing up your car for the morning commute and seeing this bright warning light on your dashboard can be a bit unnerving, there’s really nothing to worry about.

So, what does “service engine soon” mean, and why should you care? Let’s get into it.

What does “service engine soon” mean?

When the “service engine soon” light is showing on your dashboard, it means that the onboard computer has determined your vehicle needs some sort of maintenance. Much like a sticky note, this brightly colored lamp is designed to get you to pay attention and take action.

The most common reason for an illuminated “service engine soon” light is to warn owners it’s time to change the oil. Depending on the manufacturer, some vehicles will also use the “service engine soon” light to indicate other crucial fluids like coolant and windshield washer fluid are running low, or that the air filter needs to be replaced.

Other possible reasons for an illuminated “service engine soon” light are:

  • Loose or failing gas cap
  • Low transmission fluid levels
  • Low brake fluid levels
  • Dirty cabin air filter

Unlike a “check engine” light, a “service engine soon” light is not critical but more of a gentle reminder. It’s also important to remember a “service engine soon” light may not look the same on every vehicle. For example, Toyota’s comparable indicator is “MAINT REQD,” while Hondas show a small wrench to indicate it’s time to change the oil.

How does my car know it needs service?

Most “service engine soon” lights come on due to system checks done by your vehicle’s ECU (electronic control unit). This computer is like a brain for your car; it works with sensors throughout the vehicle to constantly monitor critical engine components. The only exception to this rule is oil changes, which can go by a predetermined maintenance schedule that automatically triggers the “service engine soon” light.

For example, BMW pioneered the use of a specific onboard computer that compiles data such as distance, ambient temperature, engine idle time and more into an algorithm that determines the optimal time to change the oil. This method minimizes unnecessary oil changes and helps cut down on maintenance costs. This is known as Condition Based Servicing or CBS. Many modern manufacturers like General Motors, Honda and Ford now use CBS approaches on newer vehicles.

Other manufacturers like Subaru and Toyota use a scheduled maintenance method for determining when to service an engine. For example, older Toyota vehicles will illuminate the “MAINT REQD” light at 5,000 miles since it was last reset. There are many differing opinions around which process is better, but these indicator lights should not be ignored.

Other common “service engine soon” items such as a dirty air filter or low levels of coolant are determined when a vehicle’s ECU runs system checks during startup and while driving. A dirty air filter, for example, will restrict intake air to sensors like the mass airflow sensor (MAF), which can trigger a “service engine soon” light because the ECU thinks the reason for the restricted airflow is a dirty air filter.

“Service engine soon” vs. “check engine” light

It’s easy to see why folks can get the “service engine soon” and “check engine” lights confused, but these two indicator lamps are completely different.

“Check engine” lights indicate an urgent problem to address immediately. Although there are dozens of things that can cause a “check engine” light, the most common reasons are:

  • Bad oxygen sensors
  • Loose or failing fuel cap
  • Faulty catalytic converter(s)
  • Dirty or failing mass airflow sensor
  • Bad or worn spark plugs that misfire
  • Faulty ignition coil
  • Clogged fuel injector
  • Vacuum leak
  • Faulty ignition wires
  • Failing evaporative emissions purge-control valve
  • Stuck thermostat

On the other hand, a “service engine soon” light indicates that maintenance is required soon but does not necessarily indicate an urgent problem at that moment. Think of it as a friendly reminder that your maintenance is due soon, rather than an alarm that something is seriously wrong right now.

Conclusion

Proper maintenance is key to ensuring a vehicle goes the long haul. The “service engine soon” light is there to help busy owners remember to perform key maintenance items (like air filter and oil changes) on time.

We know it’s tempting to cover it up with duct tape or reset it, so you don’t need to see it every time you turn on your car, but the real solution to a “service engine soon” light is to make an appointment and get your car in for service as soon as you can.

Frequently Asked Questions

Can you drive with the “service engine soon” light on?

Yes, you can drive with the “service engine soon” light on. You’ll want to make an appointment for scheduled maintenance in the near future, but it is not urgent.

Should I be worried if my car says “service engine soon”?

No, you should not be worried. A “service engine soon” light is just a reminder to perform scheduled maintenance.

Can low oil cause a “service engine soon” light?

Yes, low oil can cause a “service engine soon” light. Sensors in the engine look for minimum volume thresholds of oil; if oil volume falls below these thresholds, the light can be triggered.

How do you fix a “service engine soon” light?

To fix a “service engine soon” light, you’ll need to first remedy the situation that caused the light (low oil, dirty air filter, oil change, etc.) and then have the light reset. Each manufacturer will have a different reset procedure.


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Disclaimer: The above is solely intended for informational purposes and in no way constitutes legal advice or specific recommendations.