Skip the auto shop - Our mechanics make house calls

Q: Check engine light

asked by on

Is it true that the 'check engine' light can come on when the gas cap isn't on tight enough?

A: This is true, but there are countless other...

This is true, but there are countless other reasons for an illuminated Check Engine Light as well.

A loose gas cap will typically set an evaporative emissions (EVAP) system code, such as P0440 or P0455.

The EVAP system is designed to keep fuel vapors from entering the atmosphere. The powertrain control module (PCM) monitors this system and sets a trouble code if it detects a leak, such as a loose gas cap. I suggest you have a trained professional, such as one from YourMechanic, diagnose your vehicle to determine the cause of your Check Engine Light.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Anti-Skid Brake Service Required

This message comes up when the computer detects a problem that will keep it from properly controlling this system. Most of the time, it is caused by a failure in the steering angle sensor or a wheel speed sensor. I...

Q: RPMs erratic during idling, Check Engine Light on, P0174 code

Hello. The P0174 code deals with the truck running lean. That means that the PCM is restricting fuel to the injectors. This is usually caused by a vacuum leak in the engine. There could be a leaking intake gasket, or...

Q: Brakes not working

There are many reasons why brakes stop working. Low fluid level, leaking master cylinder, air in the lines, bad brake booster, etc. Since brakes are a safety concern, I suggest seeking out a professional to help you properly diagnose your...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.