Owning a car comes with many stress triggers, from traffic jams to high gas prices, but few are as anxiety-producing as a check engine light. Even worse, these dashboard red flags can come with high repair bills, especially with older vehicles.
Fortunately, not every check engine light turns into a wallet-draining experience. The challenge is knowing when to handle the issue yourself or determining when a mechanic needs to be involved. With this in mind, let’s explore check engine light fundamentals.
Common Reasons the Check Engine Light Comes On
Modern automobiles are rolling computer networks with dozens of sophisticated systems for monitoring performance, emissions, and other conditions. All this technology means there are almost limitless opportunities for something to go wrong, often triggering a check engine light. Among the most likely problem areas are five trouble spots every car owner should be aware of:
- Loose or Faulty Gas Cap: The most frequent and easily fixable cause
- Oxygen Sensor Malfunction: Affects fuel efficiency and emissions
- Spark Plug Issues: Can cause misfiring and poor engine performance
- Catalytic Converter Problems: Often expensive to repair
- Mass Airflow Sensor Trouble: Affects engine operations and fuel economy
Let’s break down each of these issues.
Faulty or Loose Gas Cap
It’s easy to overlook the importance of the gas cap, but it plays a vital role in preventing harmful gasoline vapors from entering the atmosphere. Modern cars have systems that monitor this issue. All it takes is not properly securing the gas cap after a fill-up for a warning light to illuminate. A damaged gas cap, like a bad seal or cracked housing, can have the same effect. In addition, minimizing escaping gas vapors maximizes fuel economy.
Oxygen Sensor Malfunction
Oxygen sensors monitor the amount of oxygen in a car’s exhaust system and frequently cause check engine lights. A proper air-to-fuel ratio is vital for reducing emissions and squeezing every mile out of a gallon of gas. A faulty oxygen sensor can affect engine performance, lead to emissions testing problems, and ultimately cause more damage, including to the catalytic converter, which can cost as much as $2,500 to replace.
Spark Plug Issues
Spark plug and ignition system issues frequently trigger the check engine light as well. While modern spark plugs can last up to 100,000 miles, their eventual failure can cause significant performance problems. One side effect of a bad spark plug is an engine misfire, which can eventually damage the piston and cylinder wall. Motorists can also experience hesitation, stalling, and sluggish acceleration, creating hazardous driving conditions.
Catalytic Converter Problems
The catalytic converter is a central component of an emissions control system and converts harmful exhaust elements into less toxic substances. In theory, a catalytic should last the life of a car, but low-quality fuel, physical damage to the unit, improper maintenance (see above), and driving habits can shorten its lifespan. Platinum and other rare elements are integral to converter functionality and help make this part expensive to replace.
Mass Airflow Sensor Trouble
A mass airflow (MAF) sensor measures oxygen entering the engine, ensuring an optimum air-fuel mixture. This sensitive component is vulnerable to damage and dirt build-up. Problems here result in poor engine performance, starting issues, and reduced fuel economy.
When You Can Handle Check Engine Light Problems on Your Own
Not every check engine light situation requires an immediate visit to the auto repair shop. Looking at the top five causes of a check engine light, there are a few scenarios you can at least initially tackle on your own.
Your investigation should begin with a scan for diagnostic trouble codes (DTCs). A basic code scanner costs about $20 and plugs into the OBD-II (onboard diagnostic) port on every car since 1996. Bluetooth units that use a smartphone app and a small plug-in device are also options. Many auto supply stores loan DTC scanners or perform a basic scan at no cost.
Loose or Faulty Gas Cap
DIY factor: Easy
Even without the benefit of a code scanner, it never hurts to double-check that a gas cap is secure and damage-free. Otherwise, look for codes P0455, P0456, and P0456 that can point to a problem with the cap. Loosen the cap and re-tighten it until hearing a clicking noise. Additionally, inspect the gap for a damaged seal or cracking on the threaded area or rim. Replacing a defective gas cop costs $10 to $50.
Mass Airflow Sensor Trouble
DIY factor: Moderate
While most drivers aren’t comfortable replacing a problematic MAF sensor, a more fundamental step is cleaning the unit. Be alert for code P0101, but P0100, P0102, or P0103 could also be involved. Research where the MAF sensor is located in your car (YouTube videos can be helpful) and decide if you’re comfortable accessing the component (often requiring loosening a couple of bolts or latches). A can of MAF sensor cleaner (don’t use anything else) costs about $10. Don’t touch the sensor; thoroughly apply the cleaner to remove dirt or contaminants.
Spark Plug Issues
DIY factor: Moderate to Intermediate
The truth is that replacing spark plugs isn’t overwhelmingly complex, but there are adjacent aspects that can make this task somewhat more challenging. For one, no specific trouble code points to a “bad” spark plug. You’re more likely to uncover a code that points to a larger problem like an engine misfire, with the spark plug being one of the possible reasons for the DTC. In addition, accessing the spark plugs can be frustrating, especially in modern vehicles with cramped engine bays.
Lastly, changing the spark plugs requires the right tools. Spending money for equipment (spark plug socket/wrench, torque wrench, etc.) you may never use again won’t make sense for many owners. So, while swapping out the spark plugs is undoubtedly a reasonable DIY project, it may be beyond the capability or interest of many car owners.
PRO TIP: To avoid injury or more damage, don’t attempt any DIY repair if you’re uncertain how to proceed or don’t feel confident performing the work.
When Check Engine Light Problems Require a Professional
Most of the top five check engine light problems involve some degree of DIY repair, but two areas require professional attention.
Oxygen Sensor Malfunction
Like changing spark plugs, replacing an oxygen sensor isn’t that complicated. However, access requires working under the car, which usually isn’t something the casual DIYer wants to approach. In addition, replacing the oxygen sensor can involve resetting the car’s computer, which is beyond novice DIY skills. Further, specialized tools make the job a breeze for a mechanic. In short, leave this repair to the pros.
Catalytic Converter Problems
If there’s any common repair that requires an experienced mechanic, it’s replacing the catalytic converter. Pollution control systems are highly complex and require sophisticated diagnostic equipment, especially if you live in a state with emissions regulations. Equally important, a professional technician can help identify what caused the catalytic converter to fail in the first place, avoiding a repeat of the problem later.
Warning Signs That Require a Certified Mechanic
Certain car repair situations demand immediate professional attention from an ASE-certified mechanic. Understanding these warning signs can prevent costly repairs and ensure your safety on the road. Immediate professional attention is required when you experience critical warning signs, such as:
- Flashing check engine light
- Engine missing or running roughly
- Unusual knocking or tapping sounds
- Visible smoke from the exhaust
- Loss of power during acceleration
- Transmission engagement problems
A flashing check engine light is one of the most serious warning signs. It indicates a severe engine misfire that could quickly damage expensive components.
Why a certified mechanic?
While there’s no legal requirement that a mechanic be certified through the National Institute for Automotive Service Excellence (ASE), such qualification ensures car owners that a top-level professional performs repair work. Such standards are critical in independent shops that aren’t supported with automaker-level technician training. These skilled technicians:
- Must pass a rigorous certification process
- Receive the latest training
- Have experience using the latest tools and diagnostic equipment
- Require periodic recertification
Risks of Ignoring Serious Check Engine Light Issues
Have you ever postponed a trip to the dentist or doctor only to require an urgent appointment later for a more serious condition? The same applies to automobiles, as ignoring check engine lights while your car runs can lead to severe consequences. Understanding these risks helps emphasize the importance of timely professional attention to potential car troubles. Here’s what can happen if you procrastinate getting your vehicle looked at:
- Escalating repair costs
- Decreased fuel efficiency
- Lower resale value
- Higher maintenance expenses
- Potential warranty violations
Remember how we mentioned earlier that ignoring a faulty oxygen sensor can lead to worse consequences (e.g., a damaged catalytic converter)? Let’s do the math on how this inaction can cost you.
RepairPal estimates that a new oxygen sensor costs $374 to $430. While not the cheapest repair, it’s a far lower outlay than what might lay ahead. Postpone replacing a bad oxygen sensor and, in some instances, more gas will be introduced into the combustion cycle. As a result, some fuel will go unburnt, entering the catalytic converter. This extra gas will deteriorate the delicate inner workings of the converter, eventually causing component failure.
So, instead of paying for one small repair to replace the oxygen sensor, you’re faced with the following:
- Cost of reduced fuel economy: Even a few miles per gallon drop can add up over the months.
- Paying for additional diagnostic work: A mechanic will want to rule out all possible causes of catalytic converter failure.
- Buying a new catalytic converter: An outlay costing as much as six times the price of just an oxygen sensor.
Continuing with the oxygen sensor to catalytic converter scenario, there are other critical considerations, some of which apply to other ignored repairs:
- Increased harmful emissions and carbon footprint
- Failed state inspections
- Registration renewal problems
- Local ordinance violations
How Endurance Plans Help with Engine Repairs
An extended car warranty (also called an auto protection plan or vehicle service contract) can significantly reduce the financial uncertainty associated with check engine light repairs. For instance, all Endurance Warranty plans provide primary engine coverage (as well as safeguards for the transmission and drive axles). Other options protect:
- Expanded engine components
- Core and enhanced electrical modules
- Fuel system parts
- Select emissions equipment
Meanwhile, the Endurance Supreme plan is similar to a new car bumper-to-bumper warranty, having minimal exclusions. All Endurance customers enjoy an extensive array of benefits, including:
- Repair cost protection
- Rental car reimbursement
- Trip interruption protection
- 24/7 roadside assistance (with towing and other services)
- Flexible payment terms
- Freedom to choose any licensed repair facility
Check Engine Light FAQs
What is the average cost for a check engine light diagnostic?
RepairPal estimates that basic check engine light testing and diagnosis cost $88 to $144. Prices can vary depending on the location, type of service center, and vehicle. It’s always a good idea to check the diagnostic trouble code using your OBD-II scanner or borrow one from any auto parts store like AutoZone, Advance Auto Parts, or O’Reilly. There are other ways to assess a check engine light.
Should I go to a mechanic for a check engine light?
It can never hurt to visit a mechanic if a check engine light comes on. However, you can save time and money by using an OBD-II scanner or code reader to at least identify the diagnostic trouble code (or error codes) that triggered the warning message. At the very least, you’ll be more informed when going to the repair shop. That said, any check engine light accompanied by a loss of engine performance or apparent symptoms (such as a vibration, exhaust smoke, or unusual sound) should mean an immediate trip to the shop. Further, a flashing check engine light means a more urgent situation is often best handled by towing the vehicle to the repair facility.
What are some of the most common causes of a check engine light coming on?
There can be hundreds of triggers for a check engine light, with the most common being:
- Loose or Faulty Gas Cap
- Oxygen Sensor Malfunction
- Spark Plug Issues
- Catalytic Converter Problems
- Mass Airflow Sensor Trouble
For Engine Protection and Beyond: Endurance Warranty
Discover how Endurance can protect your car’s engine and more. Request a FREE online quote or visit the Endurance online store for instant pricing and plan details. Call (800) 253-8203 for personalized help from an Endurance plan advisor.
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