Faced with the dreaded Check Engine Light (CEL)?
This automotive alert is enough to make any driver’s heart skip a beat.
While it’s easy to jump to the worst conclusions, sometimes your vehicle may simply trigger the Check Engine Light for gas cap issues.
Let’s understand the connection between a bad gas cap and the Check Engine Light and how you can fix it.
This Article Contains:
- What Are the Symptoms of a Bad Gas Cap?
- Can a Faulty Gas Cap Trigger the Check Engine Light?
- Is it Safe to Drive with the Check Engine Light on for the Gas Cap?
- How to Confirm If the Gas Cap Is Triggering Your CEL
- How to Reset the Check Engine Light for Gas Cap
- 5 Other Reasons that Can Trigger the Check Engine Light
What Are the Symptoms of a Bad Gas Cap?
Before we dive into whether a faulty fuel cap can illuminate the check engine light, here’s what we mean by a bad gas cap:
- The cap won’t tighten completely: If your gas cap doesn’t click into place, it’s not sealing properly. This can lead to dirt and grime in the fuel system.
- It has a worn or missing rubber seal: A cracked or missing rubber seal can’t keep the fuel tank airtight, leading to potential issues.
- The metal gas cap is bent or damaged: Older cars with a warped or damaged metal gas cap can’t form a proper seal, allowing fuel vapors to escape.
Now, let’s determine if a bad or loose gas cap can activate your Check Engine Light.
Can a Faulty Gas Cap Trigger the Check Engine Light?
Yes! A missing, broken, or loose gas cap can indeed cause your car’s computer to activate the Check Engine Light. Some modern cars also have a separate “Check Fuel Cap” warning light that may illuminate along with the Check Engine Light, specifically indicating an issue with the gas cap.
Here’s why:
The gas cap is integral to your vehicle’s Evaporative Emission Control System (EVAP). It seals the fuel tank and helps store fuel vapors in a charcoal canister, preventing them from escaping. This way, the EVAP reduces emissions such as carbon monoxide (CO) and carbon dioxide (CO2) in the exhaust system fumes.
However, the emissions system requires a vacuum-sealed fuel system to function correctly. If your fuel cap is loose or damaged, it can create leaks. Your car’s computer is designed to detect these small gasoline vapor leaks, which can trigger the Check Engine Light.
Note: An Evaporative Emission Control System leak is less likely to result in a flashing check engine light. A flashing check engine light typically means a more serious issue like an engine misfire.
You may wonder if the check engine light on the gas cap requires immediate attention. Read on to learn why you shouldn’t ignore it.
Is it Safe to Drive with the Check Engine Light on for the Gas Cap?
Technically, yes, but it’s not recommended.
The gas cap’s rubber seal maintains proper pressure in the fuel tank, which is crucial for reducing emission fumes and keeping the engine running efficiently. A damaged or loose fuel cap can decrease engine performance, reduce fuel economy (or fuel efficiency), and allow contaminants into the gas tank. This can potentially harm the engine over time.
So why risk such a simple repair?
That said, diagnosing a bad gas cap can be tricky in older cars with a single check engine warning light that alerts for everything. So, keep scrolling to know how you can confirm this issue on your vehicle.
How to Confirm If the Gas Cap Is Triggering Your CEL
If you’re not confident with vehicle repair, it’s best to call a mechanic to fix your engine light. But if you wish to do it yourself, follow these steps:
- Read the error code: Connect a scan tool or code reader to your vehicle’s computer and check the message it throws up. If the gas cap is at fault, you’ll see codes related to EVAP system leaks, like P0455 or P0457.
- Check the gas cap: Inspect the gasoline cap for any visible damage. Ensure it’s tightly secured with a firm “click.”
- Listen for hissing sounds: If the cap looks visibly fine, listen for any hissing sounds and gasoline smell near the fuel cap area. A hissing sound might indicate a vapor leak from the cap area.
- Replace the gas cap: If you suspect the gas cap is faulty and the CEL remains on, consider replacing it with a new cap. After replacement, drive the vehicle to see if the CEL turns off.
Fixed the cap, but the Check Engine Light is still on?
Let’s check out how you can reset it.
How to Reset the Check Engine Light for Gas Cap
Here are two ways to turn off the Check Engine Light on your car or truck:
A. Use a Code Reader
You can use a scan tool to clear the CEL. However, if the problem still exists, the light will come back on. In that case, it’s best to visit a vehicle repair shop, as the leak could be somewhere else.
B. Automatic Reset
The light may reset on its own after about three successful engine start cycles or three successful EVAP system leak tests.
However, for the EVAP leak test to run automatically, certain conditions must be met:
- The car or truck must be parked for several hours after a drive cycle, typically overnight.
- The previous drive cycle should be long enough for the engine to fully warm up; short trips might delay the test.
- The ambient temperature needs to be below 84°F, so avoid parking in hot garages.
- The gas tank should be between 1/4 and 7/8 full.
Now that you know how to reset the light, let’s examine the other potential causes of a lit Check Engine Light.
5 Other Reasons that Can Trigger the Check Engine Light
Modern cars are complex, with different electronic modules and sensors that can trigger the check engine light. Here are some alternative reasons why your CEL is on:
- Fuel system issues: Problems like a faulty fuel pump or injectors can disrupt fuel supply, lowering gas mileage and triggering the Check Engine Light.
- Faulty spark plugs and wires: Worn spark plugs or damaged spark plug wires can affect combustion and activate the warning light.
- Failing mass airflow sensor: A faulty mass airflow sensor sends incorrect air pressure data to the car’s computer, disrupting the air-fuel ratio and triggering the light.
- Damaged oxygen sensor (O2 sensor): A malfunctioning oxygen sensor gives inaccurate air-fuel data, causing the Check Engine Light to turn on.
- Clogged catalytic converter: A bad catalytic converter restricts exhaust flow, leading to misfires and triggering the light.
If your scan code reveals a related code for any of the above reasons, it’s best to consult an auto repair mechanic and resolve the issue promptly.
Put a Cap on Car Troubles with AutoNation Mobile Service
While the Check Engine Light needs immediate attention, addressing a damaged or loose gas cap is a straightforward fix that can prevent bigger problems down the road.
For added convenience, consider using AutoNation Mobile Service.
Our mobile auto repair experts can quickly resolve gas cap issues and other car troubles right from your driveway.
Contact us to book an appointment for any auto repair service.