Skip the auto shop - Our mechanics make house calls

Q: gas light loose and check engine light comes on I replaced gas cap and the issue still happens

asked by on

It says gas cap loose and check engine light comes on I replaced gas cap and it still is the same what could it be.

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

The gas cap is the most common source of evaporative emissions, which would be a reason the check engine light would come on. The evaporative emissions system is designed to limit the evaporation of fumes from the fuel in your fuel tank. We all know how easy it is to forget our gas caps at the gas station or simply not tighten it tight enough. This is the reason for the gas cap loose illumination. It often saves customers an unneeded trip to a shop for a gas cap.

Your evaporative emissions system consists of the fuel tank, vapor canister, several pressure sensors, valves and many feet of hoses running from the motor to the fuel tank. If there is a leak in any part of this system, the check engine light will turn on. At this point you need to read the code with a scanner and follow the diagnostic flow chart for that code.

It is often necessary to connect a smoke machine to the emissions system to locate the leak. Smoke machines are not cheap, so most people won’t be investing in one to diagnose their vehicle. There really isn’t another good technique to find a leak in an evap. system. You can do a visual inspection, but this will only reveal a problem if the leak is very large. The code will let you know if it is a large or small evaporative emissions leak.

If you wish to have an experienced technician to help you diagnose this, a certified YourMechanic technician can be dispatched to your location to inspect your vehicle’s check engine light and diagnose any repairs necessary.

Good luck!

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
  1. Home
  2. Questions
  3. gas light loose and check engine light comes on I replaced gas cap and the issue still happens

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: Loss of oil pressure

The oil sender may be bad causing the erratic readings. I would, however, suggest having the oil pressure tested with a gauge before replacing the sending unit for the oil pressure. If it tests okay and the pressures are normal,...

Q: when testing with code reader, testing monitors, 07 comes up saying that STS failed?

Hello. I would need to know more information about the vehicle in order to give accurate information. Depending on the year, make and model of the vehicle I would be able to determine what may be going on. It is...

Q: 02 Mitsubishi Lancer, no signal to injectors from ecm. Will the crank or cam sensor cause this? How do I check if it that or ecm?

You're right in that the crank sensor (CKP) is the primary trigger for the injection pulse. But the only way to reliably check the CKP output is with a scope. If you don't have a scope, all you can check...

Related articles

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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...