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Ask the Mechanic: Why does my engine light keep coming on?

Some people think that the check-engine light is a complete mystery. It's supposed to be a warning about potential troubles and needed auto repairs. There is no definitive one-size-fits-all answer as to why the light is coming on. However, in this "Ask the Mechanic" blog entry we'll cover the top reasons and give you a brief overview of what to do about it.

Your Gas Cap is Loose or Leaking

If your gas cap is loose or cracked it's going to cause a problem. That's right, something as simple as your gas cap is causing your check engine light to pop on, then off again. Although simple enough for even a novice to fix, generally it's not something people think of. However, a faulty cap can cost you quite a bit in gas over time and throw the air to fuel mix out of whack.

A simple solution is just to stop the car and check it out. Take the cap off, then put it back on properly, then continue driving your car. If the light goes out, viola! On the contrary, if you've had the vehicle for a while it's possible that the seal is faulty or the cap is cracked and you need a new one. This is one of the most inexpensive repairs a car owner can do. A new gas cap shouldn't cost more than $5 to $15 from the auto parts store.

An Oxygen Sensor is Bad

These sensors are part of the emission controls on your car and they send data to your car's on-board computer. The computer then adjusts the air/fuel mixture so that you get the best mileage and emit the least amount of toxic fumes. Over time, as you drive your vehicle, residue slowly starts to foul the sensors, causing decreased gas mileage and increased emissions.

Although not difficult to repair, some vehicles can have as many as four sensors. The bugger is knowing which one to replace. Although you may not care too much about the reduced mileage, the authorities may care when you go in for inspection. Additionally, running your vehicle with bad O2 sensors can foul your catalytic converter, and this can cost up to $2,000 in parts and labour. So, it's well worth the few bucks to get it repaired by a professional.

Mass Airflow Sensor

This sensor regulates the amount of fuel and air entering the engine. When the airflow sensor stops working correctly, it will decrease your car's mileage significantly. Furthermore, a faulty sensor will cause a sharp increase in emissions and your vehicle may not pass inspection. It usually goes bad because the air filter hasn't been changed regularly, if at all.

When the MAS is going bad, the engine light has usually been on for a while. The vehicle also begins sputtering, stalling or it simply starts running poorly. This is another easy fix, but it's usually best left to the mechanic because these symptoms could also be caused by something else.

Spark Plugs and Wires

Older vehicles are more susceptible to bad plugs and wires, needing them replaced every 20,000 to 30,000 km. Newer vehicles can go as long as 100,000 km before needing service. If you're no stranger to working under the bonnet, you'll have no issue replacing them on an older vehicle.

However, newer vehicle's spark plugs can be buried quite deep and it can get a little confusing to keep things sorted out properly. If the latter is the case for you, dropping off your vehicle at a reputable mechanic while you shop or have a cold brew would be far easier and less hassle all the way around.

Catalytic Converter

Catalytic converters are also part of the vehicle's emission system and are the most expensive to repair. Replacing them is usually straightforward and they are easily accessible with a hoist or car ramps. However, because they are exposed to the weather, they can be rusted in place and may require a torch to remove.

Symptoms of a bad converter are a significant decrease in mileage and little to no power when you mash on the gas. Although easy enough to find, catalytic converters contain precious metals, making them quite expensive. Additionally, some vehicles have more than one converter. It can be pretty pricey to replace them all, which is what you'll have to do if you don't know which one is at fault. This again, is something best left to a professional service center to diagnose and repair.

If you notice the engine light coming on, it may be something as simple as your gas cap which is easy to repair yourself. However, if you think it's anything more, it's probably best to get it checked over by a professional mechanic to prevent a major repair bill. If we can be of any service to you, contact us. We'll be happy to answer any questions you have.

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