3 Common Check Engine Light Causes

Auto Facts Repair Manuals
Auto Facts Repair Manuals

Let’s review the three common check engine light causes that illuminate the dreaded warning light. Although mechanics like to say there are more than 1000 reasons for a code to set in the computer’s memory, some issues become more common than others. Sidebar: This reminds me of a joke a comedian told on a popular television show. The top prize for his amateur competition came in at a whopping $250,000.

For his semi final competition, he opened his set with a frequently asked question. What would you do with the money? He said he would take that quarter million dollars and finally find out why his check engine light was on. He explained that nobody could find the reason the light was coming on. They would charge him for a fix and the light would come back on two weeks later. He figured with a bankroll of $250,000 he might be able to get to the bottom of it. Here’s the good news. The majority of vehicles that set a diagnostic trouble code often fall into the category of three common check engine light causes.

Fortunately, last week we wrote an excellent article covering the first step of check engine light diagnosis. In that article we talked about solving a check engine light problem by extracting the code with an automotive scan tool. With this information you can obtain a vehicle specific auto repair manual and follow the factory diagnostic chart for this specific failure. Nevertheless, people are hesitant to make the small investment and would like to just know what’s wrong with their car. Although I can’t tell you for sure, I can cover three common check engine light causes.

Fuel Vapor Leak Codes

Plastic Gas Cap
Plastic Gas Cap

These diagnostic trouble codes in the P0440 range are exactly that, trouble. A lot of people call them the gas cap codes, but unfortunately, it’s not always a loose or defective gas cap that causes the issues. As a quick overview of why these codes are continually in the top three common check engine light causes let’s talk about what sets these fuel vapor leak codes.

The older the automobile the more likely you’ll run into this problem. In fact, the closer your original date of manufacturer to the January 1996 model year the more likely vapor leak issues become. You can find the automobile’s build date by consulting the driver’s side door jamb sticker installed at the factory. The federal government mandated 1996 as the official year we needed to monitor and control ozone damaging gases that leak from an automobile.

Car makers had to quickly design and implement the system to meet the new strict government regulations. As the years went on the systems improved. However, the costs involved with equipping every vehicle meant the manufacturer cut costs wherever possible. They accomplish this by using cheaply manufactured plastic components produced in extremely large numbers. First, let’s be clear that the possibility exists for the gas cap to be loose or leaking.

However, it’s just as likely for the on board components responsible for pressurizing and detecting leaks to leak themselves. This is why you want to find out the exact code set and then follow the diagnostic tree chart in a factory PDF car repair manual. These ladder diagrams zero in and test individual components. This saves you a lot of time and aggravation. Not only is this one of the top three common check engine light causes, but it remains the number one code that returns over and over again.

Oxygen Sensor Diagnostic Codes

Automotive Oxygen Sensor
Automotive Oxygen Sensor

When they first started using oxygen sensors on automobiles in the early 1980s, they designed the parts to last around 100,000 miles. First of all, the company that built the vehicle really didn’t expect too much more than 100,000 miles as the vehicle’s full life cycle. Unfortunately, rising automobile costs and tightening budgets meant that these automobiles stayed on the road longer than expected.

This meant a lot of people driving around with the check engine light on. First let’s talk about why this part only lasts so long. The oxygen sensor is mounted in the exhaust stream. On vehicles newer than 1996 there are more than one of these exhaust sensing components. The sensor mounted in front of the catalytic converter can see extreme exhaust temperatures over its lifetime. Another interesting thing about this emissions control part is that it produces its own voltage.

The reason the oxygen sensor makes this three most common check engine light causes list is because they should be replaced every 100,000 miles on older cars. With the increased amount of driving even automobiles built after 2000 find the odometer reading well over 150,000 miles. If an automobile falls into this category and sets a diagnostic trouble code for an oxygen sensor, consider replacing these parts. Then clear the diagnostic trouble codes and run the automobile and see if it returns.

Throttle Body Related Trouble Codes

Intergrated Throtle Position Sensor
Integrated Throttle Position Sensor

Professional mechanics are reporting an increased amount of diagnostic trouble codes that point back to throttle body related issues. Auto repair shops like to see these diagnostic codes so they can recommend a thorough cleaning of the throttle body. There’s no question that carbon develops in this area. With that said, the reason this issue makes the common check engine light causes top three list is because of the integrated throttle position sensor.

Often when we talk about common automotive problems, these issues closely correlate to new technologies. Automobile manufacturers do the best they can to hammer out issues before they deploy new systems. Unfortunately, some issues develop after a fair amount of time and miles. As car manufacturers prepared for driverless cars a decade ago, they found it necessary to design a drive by wire system. They switched from a throttle cable and a reliable throttle position sensor to an integrated setup.

Some of these older systems are now susceptible to common problems. Also note that these integrated throttle bodies also run traction control systems and stability related technologies. Therefore, this common check engine light code often coincides with other warning lights such as the reduced power light, traction control malfunction and stability track warning message. Fortunately, as this throttle body problem becomes more common the prices of replacement parts are coming down drastically. Furthermore, the repairs remain relatively simple and fall within the skill level of many do-it-yourself mechanics.