Carbon Monoxide in Your Car

A car idling in a garage, a tailpipe blocked by snow, an exhaust leak under the chassis you haven't noticed — each of these can fill a cabin or living space with carbon monoxide in minutes. Because CO has no smell, carbon monoxide in car symptoms often get mistaken for fatigue or car sickness until multiple passengers feel ill at the same time. This guide explains how carbon monoxide (CO) can build up in or around your vehicle, the warning signs to recognize while driving, and the safest steps to take if you suspect exposure.

Quick Safety Summary

• If you feel sick while driving (headache, dizziness, nausea), pull over safely and get into fresh air immediately.
• Never idle a vehicle in an attached garage — CO can build up fast and seep into living areas.
• In winter, keep the tailpipe clear of snow; a blocked exhaust increases CO risk inside the cabin.
• Keyless ignition vehicles can run silently in a garage — always confirm the engine is off.
• Have exhaust system issues inspected by a qualified mechanic before driving again.

How Carbon Monoxide Can Happen in a Car

Cars produce CO as part of exhaust. Normally, exhaust is routed safely out of the vehicle, but several situations can create risk:

• Exhaust leaks under the vehicle that allow fumes to enter the cabin (especially at low speeds or with ventilation drawing air inside).
• Idling or running a vehicle in an enclosed or semi-enclosed space (garage, enclosed parking, repair bay).
• Wind patterns that push exhaust back toward the vehicle or into nearby openings.
• A tailpipe blocked by snow, ice, or debris, which can disrupt normal exhaust flow (winter risk).

Because CO has no smell, the absence of an odor does not mean the air is safe.

Symptoms and Warning Patterns

CO symptoms are often non-specific: headache, dizziness, nausea, unusual fatigue, and trouble concentrating. In vehicle-related exposure, a key clue is the pattern: symptoms appear or worsen while you're in the car and improve when you step into fresh air.

If more than one person in the vehicle feels unwell, or pets show unusual lethargy at the same time, treat it as a serious warning sign.

Unusual drowsiness or sleepiness while driving with the heater running can sometimes indicate exhaust fumes entering the cabin through a leak. If you notice that you feel unusually tired or foggy only while driving — and the feeling clears up after you step out of the car — consider having the exhaust system inspected. This pattern is especially worth noting if it happens consistently with the heater or defroster on.

High-Risk Scenarios

Idling in a Garage

Never run or idle a vehicle in an attached garage — even with the garage door open. CO can build up quickly and can also seep into the home through doors, walls, and ventilation paths.

Keyless Ignition / "Car Left Running" Risk

Modern vehicles can be quiet at idle. People sometimes believe they turned the car off when it's still running, especially with keyless systems. Treat "car running in garage" as an emergency scenario: shut it off if you can do so quickly and safely, then ventilate and leave the area.

Winter Snow and Blocked Tailpipes

In heavy snow, tailpipes can become partially blocked. If you're stuck, parked, or warming up the car near snowbanks, ensure the tailpipe area remains clear and never sleep in a running vehicle.

During a winter storm, snow can pack around the tailpipe in minutes while you're waiting for the car to warm up or while stuck in traffic. If you're stranded in snow, periodically check and clear the tailpipe area. Keep a small shovel or brush in the car during winter months. Even partial blockage can redirect exhaust gases under the vehicle and into the cabin through floor seams or ventilation.

Sleeping or Waiting in a Running Car

Sleeping in a running vehicle is high risk — especially if the car is parked near obstructions, in a garage, or in areas with poor airflow. If you need heat while stranded, follow official local emergency guidance and prioritize fresh-air ventilation.

Long waits in drive-through lines, school pickup queues, or rest stops with the engine running can also create risk — especially if the vehicle is close to walls, other vehicles, or structures that restrict airflow. If you regularly wait in your car for extended periods, turn the engine off when possible or park in an open, well-ventilated area away from obstructions.

What to Do If You Suspect CO in Your Car

1. If driving: safely pull over as soon as you can.
2. Turn the engine off and exit the vehicle into fresh air.
3. Check everyone for severe symptoms (confusion, fainting, chest pain, trouble breathing). If present, call emergency services.
4. Do not continue driving if symptoms are ongoing or if you suspect an exhaust leak.
5. If you were idling in a garage: leave the garage/home area and call for guidance if anyone feels unwell.
6. Arrange an inspection by a qualified mechanic — describe symptoms and request an exhaust system check.
7. Do not "test" the problem by sitting in the car with the engine running.

Emergency response guide: What to do if you suspect a carbon monoxide leak.

Prevention Tips for Vehicles

• Do not idle in an attached garage — back out immediately if you need to warm the vehicle.
• Get exhaust system issues inspected promptly (loud exhaust, rattling, visible damage).
• If you regularly drive in snow, keep the tailpipe area clear when parked or stuck.
• If you frequently sit in a parked car (work breaks, waiting), choose well-ventilated outdoor areas and avoid enclosed structures.
• In shared buildings, avoid running vehicles near doors, windows, and ventilation intakes.
• At home, maintain CO alarms — vehicle exhaust can affect indoor air near attached garages.
• Schedule an exhaust system inspection during routine maintenance visits — a mechanic can check for rust, cracks, loose connections, and damaged gaskets that could allow exhaust leak carbon monoxide into the cabin.
• Pay attention to warning signs: unusually loud exhaust, vibrations you haven't felt before, visible rust or holes under the vehicle, or an exhaust smell inside the car.
• If your vehicle is older or has high mileage, more frequent exhaust inspections are worthwhile — corrosion and wear increase the chance of leaks over time.

Full prevention checklist: Prevention of carbon monoxide poisoning.

Common Mistakes With Vehicles and CO

• "Just warming it up for a minute" — CO can reach dangerous levels in an attached garage within minutes, even with the door open.
• Assuming keyless cars turn off automatically — some vehicles stay running quietly; always confirm the engine is off before leaving.
• Sleeping in a running car — any obstruction to exhaust (snow, wall, ground) can redirect CO into the cabin.
• Ignoring exhaust rattles or smells — unusual exhaust noise or visible damage may indicate a leak that could admit CO into the cabin.
• Relying on open windows as a fix — windows reduce exposure but don't eliminate it; stop the source and get the vehicle inspected.

Sources & References

• CDC — Carbon Monoxide Poisoning
• US CPSC — Carbon Monoxide Information Center
• NHTSA — Vehicle Safety
• NHS — Carbon Monoxide Poisoning

Last updated: February 15, 2026