Skip the auto shop - Our mechanics make house calls

Q: Gas cap loose and check engine soon light comes on

asked by on

My gas cap says loose I replaced gas cap and it still says it and check engine light comes on what could be the problem

My car has 167000 miles.
My car has an automatic transmission.

A: Hi there. The vehicle's computer can th...

Hi there. The vehicle's computer can think that the gas cap is loose simply from there being a leak in the EVAP system. This will occur if the gas cap neck is not sealing well to the cap, or if there is a leak someplace else in the system and the check engine light will keep coming on and off.

Smoke test the system to find the leak as it may be a solenoid or a small hose leak that can be hard to find. If you are planning on having this EVAP system problem checked, consider getting a certified mobile technician, such as one from YourMechanic, to come to your location and see why the check engine light keeps coming on. If you suspect that the problem is due to a loose gas cap, get the cap inspected as well.

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・Save up to 30%

Get a quote

What others are asking

Q: My gas tank (where I open the lidoor and actually put the gas pump in) is literally detached from the car.

You will need to replace the plastic retainer for the fuel fill pipe. Have a certified mechanic, like one from YourMechanic, inspect the gas cap and order all the necessary parts. They will also help you install it. The mechanic...

Q: I got a alternator replaced on my car and now the Check Engine Light is on with the Battery Light. My headlights are still blinking.

Hi and thanks for contacting YourMechanic. This sounds like there is a loose ground or a wire was not hooked up to the alternator correctly. Check all of the wiring when that was removed when the alternator and battery was...

Q: Which make-model is best with least known problems

Hi there. I understand your needs and how cold it can get up there. However, trying to pick which used make/model is the best without a pre-purchase inspection is a bit like predicting the weather. One of the things I...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...