Car Maintenance Tips: My Check-Engine Light Won't Go Off

It’s the worst when you’re driving and you realize, “Oh no, my check-engine light won’t go off!” Unfortunately this warning light is not something you can just wish away. 

Here are car maintenance tips for what to do if that light stays on—and some possible triggers that caused it, from most common to least.

1. The first thing you should do when your check-engine warning light remains lit is check the gas cap, if your vehicle has one. A loose, ill-fitting or broken fuel cap can cause a vapor leak somewhere in the fuel-tank system, says Ford senior master technician Jim Twitchell. The Environmental Protection Agency has mandated that fuel-tank systems must be sealed, because as gasoline evaporates, it releases hydrocarbons into the air as contaminants, Twitchell explains. “Any break in that seal can cause a system warning light to be set.”

2. If adjusting your gas cap doesn’t do the trick, you’ll need to take your vehicle into a Ford Dealer Service Center to be checked. The check-engine light is activated when the engine’s computer has detected a code signaling that something is wrong; your service technician has a special tool to read the code and pinpoint the problem. If your state has a smog-check requirement, your vehicle will automatically fail the test if the check-engine light is on, notes Twitchell. So before doing a smog test, be sure to take care of any issues that would trigger this light. Besides a loose gas cap, other problems that could activate the check-engine light are:

• Damaged spark plugs, wires or coils. Spark plugs, wires and coils can be harmed by pressure-washing the engine (don’t force pressurized water into any wiring, fuse boxes, etc., under the hood, Twitchell advises) or by rodents gnawing on wires. That’s right: On cold evenings, your warm car is inviting to rats and mice, especially if you park near rodent food sources (such as garbage cans), or prime rodent nesting areas, such as ivy or other heavy groundcover. 

• Thermostat issues. Your check-engine light can come on if your vehicle’s thermostat detects overheating or if your car isn’t getting up to the correct engine temperature in the proper amount of time. 

• Malfunctioning catalytic converter. The catalytic converter cleans the exhaust coming from the engine before it’s released into the atmosphere. “The insides of the ‘cat’ may crack and/or come apart over time, and this can prevent these exhaust gases from getting out,” Twitchell explains. In addition to the warning light, you may notice a reduction in power and sometimes a rattling noise.

• Faulty mass airflow sensor. This sensor reads the amount of air coming into the engine. Either too much or not enough air can cause the check-engine light to come on. “The mass air sensor measures how hard the engine is working and calculates the load,” says Twitchell. A dirty or torn air filter can lead to problems with the sensor. “The seals keep dirt and other foreign elements out of the mass air sensor. Choosing a cheap replacement air filter can lead to an expensive repair down the road.”

• Malfunctioning oxygen sensor. The oxygen sensor measures the oxygen coming out in the vehicle’s exhaust. This information is used by the engine’s computer to determine how long the fuel injector stays on, and a damaged sensor can activate the check-engine light. (Twitchell points out that the oxygen sensor fails much less often in newer cars, so if your vehicle was built within the past five years, this is less likely to be the cause of the warning light.)

• Faulty exhaust gas recirculation valve.This valve takes exhaust gases and puts them back into the engine’s combustion chamber. If this valve becomes stuck either open or closed, the result can trigger a check-engine light. (Newer vehicles usually don’t have this valve.)

The most important thing to remember: Don’t ignore your check-engine light, because if you wait too long to have your car checked, you risk erasing the engine codes, which makes it more difficult to diagnose the issue. Once you fix the underlying problem, the check-engine light should go off. It’s as simple as that.