Can Refueling Your Car Contaminate IID Readings? Learn the Science Behind Why

You might be shocked to see a positive reading on your ignition interlock device right after pumping gas. Learn why this happens, what to do, and how to prevent it.

What the heck? You refueled your car at a gas station like normal, but when you blew into your IID, it registered a positive. You haven't had a drink in weeks, and you didn't eat or drink anything before the test.

So what happened? The good news is, you're likely not in trouble. It may be a contaminated reading caused by fuel vapors, not alcohol use. Here's what's really going on, how science explains it, and the steps you can take to stay compliant and stress-free.

This blog isn't considered legal advice; always consult with a qualified DUI attorney if you have specific questions. If you're convicted of a DUI and need to learn more about ignition interlocks, call our team at (888) 283-5899.

How Do Ignition Interlock Devices (IIDs) Work?

An ignition interlock device, also called a car breathalyzer, measures your breath alcohol concentration (BrAC) before your vehicle can start. Most IIDs use fuel-cell technology, a sensor that reacts only to ethanol, the type of alcohol found in drinks.

When you blow into the mouthpiece, your breath passes over a platinum-based sensor that generates an electrical current. The stronger the signal, the higher your BrAC. If you blow a BrAC above your state's limit, usually between 0.02 percent and 0.04 percent, the IID prevents your car from starting.

Can Refueling at Gas Stations Contaminate Your IID Readings?

Yes, it can happen, but it is rare. Gasoline fumes contain small amounts of ethanol and other volatile organic compounds. When these fumes mix with the air you breathe while standing near a gas pump, trace vapors can linger in your mouth or lungs.

If you immediately take a breath test after refueling, those vapors may enter your IID and temporarily mimic alcohol. The result is a short-term reading that looks like a failed test, even though you have not consumed alcohol.

How Common Is It for Refueling to Cause Contaminated IID Readings?

It is uncommon, but not impossible. Reports show that most contaminated readings happen when users blow into the device right after handling the pump or standing in concentrated fuel vapors. Because interlocks are extremely sensitive, even a small amount of ethanol in the surrounding air can register as a trace BrAC level.

Most of the time, these readings clear quickly during a retest once the air around you stabilizes. Knowing when and where you test makes a big difference in preventing unnecessary stress.

What to Do If Refueling Results in a Contaminated IID Reading

If you believe your ignition interlock reading came from fuel vapors, stay calm. You can take practical steps to protect yourself and your compliance record.

States Where Your IID May Prompt a Retest

Your state may require random retests, which occur after your car starts. If the first test shows contamination, you usually have the chance to retest within minutes. Passing that retest confirms to your monitoring authority, such as your probation officer, court, or state monitoring agency, that the first reading was environmental and not alcohol use.

Document the Contaminated IID Reading

Write down what happened right away. Note the time, date, and location. For example: "Refueled at 3:45 p.m. at Shell station, immediate test showed 0.02."

Use the Intoxalock Mobile App to view your reading history, appointment reminders, and test results in real time. Documentation explains any irregular readings in your compliance record, which is the official record your state uses to track your ignition interlock performance.

Contact Your IID Monitoring Agency

After documenting, contact your monitoring authority or Intoxalock customer support at (888) 283-5899. Explain that you refueled moments before testing and believe gas vapors caused the reading. Our team is available 24 hours a day, seven days a week, and can walk you through the next steps, including whether a service check or calibration is needed.

If you are unsure who to contact, our specialists can identify your state's reporting authority and explain how to reach them. Quick communication shows responsibility and keeps you compliant with your ignition interlock program.

Can Contaminated Interlock Readings Cost Me Money?

Not necessarily. Each state handles service and lockout fees differently. If you experience multiple failed starts or your IID does not clear after a retest, schedule a visit to an Intoxalock service center for recalibration.

At Intoxalock, affordable lease pricing starts as low as $1.96 per day, with flexible monthly or bi-monthly payment options to fit your budget. If you ever face a questionable reading, our State Specialists can determine whether IID service is required and how to minimize or avoid added costs.

What NOT to Do If You Get a Contaminated IID Reading

If you receive an unexpected reading after refueling:

• Do not disconnect your device. Removing or tampering with it can violate your ignition interlock program requirements set by your state or court.
• Do not drive until you pass a retest. Wait a few minutes, safely walk away from the fueling area, and retest when the air clears.
• Do not panic or ignore it. A calm, documented response protects you and keeps your compliance record intact.

How to Prevent Contaminated Breathalyzer Readings When Refueling Your Car

The best approach is prevention. Small adjustments to your routine can eliminate exposure to vapors before testing:

• Always turn off your ignition while refueling.
• Step several feet away from the pump while waiting for your tank to fill.
• Avoid testing immediately after closing your gas cap. Wait at least one to two minutes in clean air.
• Open your windows before taking a test if you smell gas inside your car.

Following these steps makes it far less likely that fuel vapors can interfere with your next breath sample.

What Else Might Cause a Contaminated IID Reading?

Gasoline is not the only product that can produce a contaminated sample. Other contaminant triggers include:

• Alcohol-based hand sanitizers
• Windshield washer fluid and glass cleaners
• Mouthwash, breath spray, or cough syrup
• Energy drinks or fermented foods consumed just before testing

In each case, trace ethanol vapors can enter your breath temporarily. Waiting five to ten minutes before testing usually eliminates false readings.

Contaminated Interlock Readings vs. False Positives

A contaminated reading happens when vapors or products interfere with your breath sample. A false positive occurs when your device records an inaccurate BrAC value.

Contamination is environmental and short-lived. A false positive is a recorded reading that may need to be reviewed or cleared during calibration. Understanding this difference helps you communicate clearly with your monitoring authority and avoid unnecessary penalties.

Prevention and Action for Contaminated Breathalyzer Readings

Getting a contaminated ignition interlock device reading can be frustrating, especially when you have done everything right. Understanding how environmental factors like gas fumes work gives you peace of mind and prevents future issues.

With over 5,500 locations nationwide, 35 years of experience, and 1.2 million licenses regained, Intoxalock^® makes the IID process as easy and transparent as possible. If you have questions about your device, your readings, or your next service visit, talk to a State Specialist anytime at (888) 283-5899.

We are here 24/7 to help you stay compliant, confident, and in control so you can get back on the road safely.

By staying informed and prepared, you can turn an unexpected reading into just another step toward regaining complete driving independence.