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Engine Light On? Could Be Bad Gas!

Why is your check engine light on?

When your car’s internal computer detects a problem in the engine or transmission, it activates the check engine light. This light can signify various reasons, ranging from minor issues like a loose gas cap to more serious concerns such as a faulty catalytic converter or even a sign of internal engine failure. Ignoring this warning can transform what might be a potentially quick fix into a costly and time-consuming repair.

The common reasons for your check engine light to turn on include not just a loose gas cap but also internal problems with the engine, theft of the catalytic converter, faulty spark plugs or wires, malfunctioning oxygen sensors, or a damaged mass airflow sensor. Sometimes, using bad gas can also trigger the light. Remember, addressing these issues promptly can save you from more significant problems down the road.

What to do when your check engine light comes on

When the check engine light illuminates, it’s crucial to pay attention to how your car is driving. Does it feel off? If so, it’s wise to reroute to the nearest mechanic to get your car checked out. If your car is running fine, there could still be a couple of simple solutions. Often, a loose gas cap is one of the most common reasons for the light to go on. Ensure your gas cap is screwed on securely and in good condition.

For those whose vehicles are designed to run on premium gas with an octane grade of 91 to 94, using regular gas at an octane level of 87 can cause the engine to struggle. This issue can usually be safely solved by having a professional drain your gas tank, especially if you suspect bad gas is the cause. However, if you must drive until the tank is empty, watch out for signs of overheating or poor engine performance, as they may indicate severe damage. If you suspect something else caused your light to turn on, a foolproof method is to read the diagnostic code in the car’s internal computer. You can do this at home with an OBD-II scanner or at a local service station where a mechanic can determine the correct fix.

Why you shouldn’t ignore your check engine light

When your check engine light illuminates, it’s crucial not to confuse it with the maintenance required light, as they are unrelated. The maintenance required light typically goes on when your car is due for routine service, like an oil change. In contrast, the check engine light is an indication of something unexpected that has occurred within the vehicle’s system. Later models of cars might have different colors and modes for this light to help determine how severe the issue is. If it flashes intermittently or glows red, it’s a clear sign that you should visit a mechanic as soon as possible.

Depending on your car’s make and model, a solid yellow or orange light may indicate a lower severity problem, but it still warrants an appointment to diagnose and fix the problem. Ignoring this light can lead to more significant issues down the line.

What are the implications of ignoring your check engine light?

Ignoring the check engine light and putting off a visit to the mechanic can lead to more costly and time-consuming issues to deal with in the future. The initial problem that caused your check engine light to turn on could get worse, potentially impacting crucial aspects of your car’s engine or transmission. This neglect could result in long-term damage that your car insurance may not cover. Moreover, you won’t be able to pass your next car inspection until the check engine light is off and the problem is resolved. Your best option is to address the issue quickly. If you’re concerned about affording unexpected repairs, it’s wise to consider options like mechanical breakdown insurance.

The ‘check engine’ light came on after I had my car refueled. What happened?

If you suddenly see the check engine light come on after getting gas, a few reasons could be behind it. Often, it’s as simple as a loose fuel cap or a gasket that’s gone bad, leading to a damaged vacuum hose. Modern cars, especially those built since the ’90s, have a complex system known as the evaporative emission control (EVAP). This system is designed to collect fuel vapors and prevent them from being released into the atmosphere, keeping the environment clean. It captures vapor from the fuel tank and stores it in a separate canister, which is then siphoned into the intake manifold in controlled amounts. The ECU of the car monitors this sealed and pressurized system while the engine is running. If it detects a loss of pressure, it indicates a problem, typically a leak. This minor issue can often be resolved by ensuring the fuel cap is secure and intact.


Possible causes

When your car’s check engine light turns on, especially after being refueled, it could be due to various factors. A common issue is a loose fuel cap or a bad fuel-cap gasket that has degraded, causing a loss of pressure in the fuel system. This can lead to gas vapors being released into the atmosphere, a condition detected by sensors when the engine is running. Overlooking this can trigger the check engine light. Another possibility is the overfilling of the tank at the fuel-station, which can cause the EVAP system – comprising rubber hoses, valves, and a canister that collects and stores fuel vapors – to malfunction. An air-tight seal is crucial for this system to function optimally, and twisting open a damaged cap can disrupt this, leading to emissions problems. If any of these parts are not in good shape or if overfilling causes the valves in the canister to stick, it can result in the check engine light being activated.

What to do

If you face a situation where the check engine light suddenly turns on, especially after refueling, the simplest solution might be right at your fingertips. Start by checking if the fuel cap is tight. A loose cap can easily cause the light to come on. Ensure your car’s engine is turned off when the tank is being filled and avoid overfilling it. If the problem persists, the next step is to use an OBD-II scanner to check the code. Often, it could be something like P0442, indicating a leak in the EVAP system.

While seeing the check engine light can be concerning, it’s not always a sign of a catastrophic issue. However, it’s important to address the problem immediately to avoid bigger problems that might arise later. In most cases, it’s okay to drive for a few days until the issue is fixed, but try to get it resolved before you embark on longer trips.

Will bad gas cause your check engine light to come on?

Technically, bad gas can cause your check engine light to come on, often due to a misfire. In my over 30 years as a mechanic, I’ve seen this happen, but it’s rarely the actual cause. It’s the first thing often mentioned by customers, yet it seldom turns out to be true. It’s essential to gather facts, not just guesses. The first fact to be obtained is the actual code number that is stored in the car’s system.

For example, at VW dealers in the early 2000s, 1.8turbo engines often showed misfire codes when running on Arco brand gas. We recommended switching to Chevron, Shell, or 76 – all top tier brands with the correct octane level. Always run what the car recommends, nothing more, nothing less. For instance, a 1.8t engine that requires 91 octane will struggle with 87 octane, as observed through a scan tool, showing a pull of degrees in ignition timing advance. This can couple with crappy gas to cause a misfire.

Moreover, worse cleaning additives in lower-quality gas can clog injectors, altering their spray pattern and turning fine atomized fuel into dribbles or liquid, leading to misfires. Therefore, it’s crucial to run good gas, use the proper octane, and consider getting them cleaned and flow balanced every 100k miles. This is particularly important in direct injection or forced induction engines, where pressures from the combustion chamber and boost can force carbon into them.

In one instance during a smog check in California for renewal of registration, a car that tended to stall needed its throttle body cleaned. The check engine light came on, and error codes were read. A 420 code, indicating a problem with the catalytic converter system, was diagnosed when using Arco regular, the cheapest option. Switching to a better gas like Chevron or Shell with 91 octane and driving a hundred miles or so often clears the issue. It’s a process of driving off the remaining bad gas and filling up with the good stuff to pass the smog test.

In a personal experience with a 2005 Saturn Ion, switching to the most expensive Chevron grade and driving it for a while resolved the issue, as confirmed by a likable smog guy, John. The car passed, reinforcing what I later found in the manual: using a lower grade of gas can cause the engine light to come on, which clears by running a better quality of fuel. Now, I always opt for more expensive gas.

Will a check engine light come on if my car runs out of gas?

When your car is running out of gas, it’s not just a good situation to avoid; it may also cause your check engine light to come on. Modern cars are equipped with a fuel level sensor that monitors the amount of gas in the tank. As the fuel level drops, this sensor sends a signal to the car’s computer, usually triggering the low fuel warning light, which is different from the check engine light and often looks like a gas pump or a fuel gauge. However, if you ignore this warning and continue driving until the tank is empty, it could trigger a drop in fuel pressure, affecting the performance of the engine and its components. This might lead to the engine overheating, the fuel pump failing, or the catalytic converter malfunctioning due to unburned fuel in the exhaust system. Additionally, air entering the fuel lines can create air bubbles that interfere with the flow of fuel to the engine, potentially causing it to misfire or stall, which can then set off the check engine light. While it’s not guaranteed to happen every time you drive long with low fuel, how your car reacts to the loss of fuel pressure and how sensitive its system is to detecting faults can make a difference. To avoid this problem, always keep your tank at least quarter full and refill it as soon as you see the low fuel warning light.

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When exploring the relationship between bad gas and the check engine light, a curious question arises: “What happens if my car runs out of fuel?” In this context, there are two different scenarios to consider. When you’re driving with remaining fuel sloshing in the tank, the car is constantly regaining and losing pressure. This can piss off the Engine Control Module (ECM), leading you to see the light on your dashboard. In most cars (except Ford), the computer needs to wait and verify the failure.

A personal anecdote comes to mind: once, while sitting idling, my car ran out of fuel. The ECM was definitely not happy. As the fuel pressure drops, the engine may stall, which can set off codes related to fuel supply and RPMs dropped. This is a clear indication to the car’s system that something is not right, triggering the check engine light as a warning.

Why does my check engine light come on after getting gas?

There are a number of reasons why your check engine light comes on after you’ve filled up your fuel tank. When you open your gas cap, you are essentially opening a critical part of your vehicle’s fuel system – the evaporative emissions system. This system is designed to collect fuel vapors and prevent them from being released into the atmosphere. If the gas cap is not properly secured or if it’s leaking due to a worn-out o-ring, it can compromise the system’s integrity. This can cause the sensors in the system, which are still working even when the car is being refueled, to detect faults.

Another common cause is overfilling the tank, which interferes with how the system operates and detects these faults. If you’re experiencing this issue, the fix is often easy: make sure to turn off your car when you fill up, avoid overfilling the tank, and ensure that your gas cap is secured. If the light remains on, it might be necessary to have the issue diagnosed by a professional.

How do you fix a check engine light that is on after getting gas?

If your check engine light comes on after getting gas, a quick and effective solution often involves checking the code responsible for triggering the light. Many AutoZone stores or quick oil change places offer this service for free. These codes can often point to an EVAP system issue, be it a large or small problem. One common trigger is a loose gas cap – hence the light can sometimes indicate nothing more serious than a need to tighten the cap.

After tightening the gas cap, you can reset the codes using a code reader. If the light comes back on after being reset and tightened, it may signal a larger problem with your vehicle. In some cases, you might choose to leave the engine light on for a while as it might clear eventually once the issue is fixed. However, it’s always best to investigate the underlying cause to avoid potential complications.

What are the symptoms of a bad gas cap, and how long after a loose gas cap will check engine light come on?

A bad gas cap can be detected by the ECU within minutes, though some cars might have a reporting delay. The test to detect this is trivial, but sometimes a rapid temperature change can trigger a false alarm, which is monitored by the car’s system. The normal-pressure in the fuel tank is maintained by the evaporative emission control system (EVAP), which includes a canister only accessible when the ECU activates an electric solenoid. It’s a sealed system, so any loss of pressure without activating the solenoid points to a leak, often at the gas cap, which is the culprit in the majority of cases.

Symptoms of a bad gas cap include a worn-out rubber gasket, leading to an erratic idle. This occurs because any pressure build-up in the tank, meant to be burnt by the engine, is accounted for as fuel volume. However, with a bad gas cap, Nonburnable air replaces the fuel, causing the engine to receive mostly air instead of the fuel/air mix, particularly noticeable at idle.

Another thing to monitor is the sound when you open the gas cap. If you hear a Psst sound, like something trying to re-equilibrate the pressure, it’s indicative that something is wrong with the EVAP system. In such cases, it’s recommended to visit your favourite garage for a check-up.

Why does your check engine light come on when your gas gets low?

The check engine light, or MIL (Malfunction Indicator Lamp), coming on in response to a low fuel condition is not a direct diagnostic system display. In modern vehicles, there is no specific Diagnostic Trouble Code (DTC) in the OBD (On Board Diagnostics) system that directly correlates to low fuel. However, in some older cars, there was a Check Gauges light that would turn on for an unspecified condition, usually indicated elsewhere in the gauge cluster. This light was meant to prompt drivers to review their gauges, including the fuel level, and refuel as necessary.

In current vehicles, the “Check Engine” light illuminates when there is a malfunction detected by the car’s control module or onboard computers. This light typically does not go out until the malfunction is cured and the corresponding code is cleared with an automotive scan tool. Therefore, while a low fuel level might trigger other warnings, it’s not commonly linked directly to the activation of the Check Engine light in most modern vehicle diagnostic systems.

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Why Does Refueling Trigger My Check Engine Light?

The check engine light coming on after getting gas can be attributed to a number of reasons, often related to emissions fault codes. One of the most common leak issues is a loose or misplaced filler cap, which can cause a major leak code. Similarly, a failed seal on the cap might lead to a minor leak code. Your car’s fuel tank has a ventilation system to manage tank pressure changes, allowing air to enter when needed while preventing fuel vapor from escaping and being pulled into the engine’s intake system.

Another issue could be a mechanical failure or debris causing the charcoal canister shutoff valve to stick open. This problem can be exacerbated by consistent overfilling or age. The purge valve sticking open or closed and hard system leaks like a cracked hose or a seal at the level sensor assembly could also trigger the light. Overfilling the tank may affect the charcoal filter, causing the valve to stick and disrupt the system designed for vapor, not liquid fuel.

The fuel tank’s semi-flexible nature means the weight of the fuel can distort the tank, leading to leaks at dried or failed seals, with the leak’s severity often being fuel level dependent. In some unique cases, weird ones like an installation gone awry—for instance, a low-jack transmitter installed incorrectly—can cause issues. If installers accidentally screw mounts through the floor under the seat into the fuel tank, it can result in a minor leak code when the tank is full and the weight of the fuel pulls down on the screw. Plastic tanks can also be cracked at a seam, and issues like distortion and swelling from substances like E85 or MTBE, as well as metal tanks with braised hose junctions that have separated, can contribute to this problem.

Does Running Out of Gas Light Up Your Check Engine?

Imagine you’re driving and your car is running out of gas. You might think it’s just a matter of a walk to the nearest gas station to buy a can or a couple of gallons and then back to your vehicle to restart it. However, there’s more to this situation than meets the eye.

When a car runs low on fuel, fuel pressure in the system may start fluctuating. This could lead to a misfire as the engine starts struggling with inconsistent fuel supply. It’s indeed possible for the check engine light to come on in such scenarios. I remember a friend who faced a similar issue; their car’s check engine light turned on after running extremely low on fuel.

Now, after refueling and restarting, you might notice the Check Engine light remains on. This can be unsettling, but it’s often due to the car’s onboard diagnostics system running through its ignition cycles and clearing any stored codes. These codes can range from a lean exhaust to a random misfire, triggered by the initial lack of fuel.

In conclusion, while running out of gas is a fairly common occurrence, it’s important to understand the potential implications it has on your car’s health and the warnings it might trigger, such as the check engine light.

Why would a new gas cap cause the “check engine” light to shut off?

When considering how bad gas can trigger a check engine light, it’s intriguing to explore how something as simple as a fuel cap can play a pivotal role in this scenario. Vehicles require a well-sealed fuel system to control emissions and maintain a slight vacuum. This vacuum is essential as it prevents fuel vapors from escaping into the atmosphere, a key aspect of modern vehicle emission systems.

From personal experience, I’ve learned that a poor seal on the fuel cap can disrupt this balance. When the seal fails, it causes a vacuum leak in the engine’s intake system, leading to performance issues and, yes, the illumination of the check engine light. The system runs a check and detects this anomaly, notifying you of the issue.

Typically, the solution is straightforward: either tighten the existing cap if it’s loose or need a new cap if the old one is damaged. It’s a matter of maintaining the integrity of the fuel system, ensuring proper vent and emissions control. So, a new gas cap can indeed cause the check engine light to shut off, addressing a small but crucial part of your vehicle’s health.

Is it a bad sign if a check engine light comes on after getting gas?

When discussing bad gas and its impact on the check engine light, a common yet often overlooked scenario is what happens when this light illuminates after getting gas. I’ve encountered this a number of times myself. Sometimes, the attendant didn’t tighten the gas cap properly, and as a result, the check engine light came on.

In my experience, simply tightening the cap usually resolves the issue. It might take a day or two for the system to reset and the light to go off, but everything turns out to be fine. If your car’s check engine light comes on after refueling and you suspect a loose cap, wait a couple of days after tightening it. If you don’t feel comfortable doing this yourself, know that most auto parts stores will diagnose the issue for free. This simple check can save you time and worry, addressing a small but significant cause of check engine alerts.

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