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

asked by on October 27, 2016

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.

Check Engine Light is on Inspection $94.99 - $114.99 Get a Quote

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!

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Detecting strong gas smell.
The EVAP system is used to prevent fuel vapors from escaping into the atmosphere. The powertrain control module (PCM) monitors this system to ensure it is completely sealed. If a leak is detected, the PCM will illuminate the check engine...
Can't keep antifreeze in car
If your vehicle is losing coolant (antifreeze) you probably have a leak. I recommend having a trained technician, like one from YourMechanic, pressure test your cooling system to locate where the coolant is leaking from (https://www.yourmechanic.com/services/coolant-is-leaking-inspection). From there, they will...
How can I start my car remotely?
There are a number of after market options (https://www.yourmechanic.com/article/how-to-buy-a-good-quality-remote-starter) available. They require installation by someone who can read a wiring diagram and connect to the vehicles starting and PCM systems. If your comfortable working on your own car, google remote...
Why is my car stalling when reaching operating temperature?
Hello. This is a common problem on this generation of Impala. Some solutions I have seen work with this problem are replacing the mass air flow sensor (https://www.yourmechanic.com/services/mass-airflow-sensor-replacement) or crankshaft position sensor (https://www.yourmechanic.com/services/crankshaft-position-sensor-replacement). The mass air flow sensor relays to...
Oil pressure low
Hi there, thanks for writing in. It's very possible that the crank position sensor (https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-crankshaft-position-sensor) is either sending faulty data or is broken and needs to be replaced. The car is shutting off automatically as a safety precaution due low...
Car check engine light is off. Car accelerates by itself in drive from 0 to 60 miles an hour. Replaced aci, no codes on computer, 1999 Ford Taurus
Hello - your Taurus has a Recall (#98V204000) against the cruise control, which can cause unintended acceleration. In a related later issue, new Taurus models had problems with twisted accelerator cables - again, from the cruise control, which may have...
I have a 2006 Acura TL it's leaking green fluid and running hot
You should not let the engine get low on coolant until the leak is identified and fixed. You may have a water pump or radiator leaking. You should have the cooling system pressure tested to locate the leak in the...
I have a 2000 Chevy Blazer automatic. When I turn the key over it starts grinding horribly as soon as it cranks over. Ive replaced
If the starter motor does not release once the engine is running, the cause could be starter misalignment or failure of the circuit to open, and release the starter solenoid, the instant you release the ignition key. If the noise...

Related articles

P2067 OBD-II Trouble Code: Fuel Level Sensor B Circuit Low
P2067 P2067 code definition? Fuel Level Sensor B Circuit Low What the P2067 code means The Engine Control Module (ECM) utilizes a sensor either built into the fuel pump, or into the fuel tank, which communicates to the ECM the...
P2193 OBD-II Trouble Code: System Too Lean at Higher Load Bank 2
P2193 P2193 code definition System Too Lean at Higher Load Bank 2 What the P2193 code means P2193 is an OBD-II generic code for the Engine Control Module (ECM) detecting the fuel control has reached its rich limits when the...
P0618 OBD-II Trouble Code: Alternative Fuel Control Module KAM Error
P0618 means an error with the alternative fuel control module, due to its malfunction or electrical issues within the CAN.