Carbon monoxide (CO) has no colour and no smell, and a running engine makes it. In winter the risks gather in a few places: warming up a car in the garage, sitting in a car stuck in snow, and driving with the tailgate open. This is what the CDC and NHTSA say.
Never run the car in an attached garage
The CDC is plain about it: do not run a vehicle in a garage attached to a house, "even with the garage door open". In a detached garage, open the door to let fresh air in while the engine runs. Warm the car up outside.
Stuck in snow: clear the exhaust pipe
Snow packed around the tailpipe can force exhaust into the car. If you are stranded, NHTSA says to clear any snow from the exhaust pipe and to run the engine only occasionally, just long enough to keep warm, and not to sit for long periods with the engine running and the windows up. What else to do is in the winter emergency kit guide.
The open tailgate trap
Driving with only the tailgate or boot open pulls exhaust into the car or SUV. If you must, the CDC says to open the windows or vents too.
Have the exhaust checked once a year
The CDC notes that a small leak in the exhaust system can let CO build up inside the car. A yearly check of the exhaust system catches it. Some recalls concern exhaust leaks too: check your car by VIN.
The warning signs
The CDC lists the most common symptoms as headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as "flu-like". People who are asleep or have been drinking can be overcome before they notice anything. Babies, older people, and people with heart disease, anaemia or breathing problems are more at risk.
If you suspect CO: turn the engine off, get everyone into fresh air at once, and call emergency services or a doctor.
Quick answers
Is it safe to warm up a car in the garage with the door open?
Not in a garage attached to a house. The CDC says never to run a vehicle in an attached garage, even with the garage door open. In a detached garage, open the door while the engine runs, or warm the car up outside.
Can you get carbon monoxide poisoning in a car stuck in snow?
Yes, if snow blocks the exhaust pipe. NHTSA advises clearing snow from the exhaust pipe and running the engine only occasionally, just long enough to keep warm.
What are the symptoms of carbon monoxide poisoning?
The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. If you suspect it, turn the engine off, get into fresh air and call emergency services.
More winter safety
- Winter car emergency kit: what to carry, and what to do if you are stranded
- Winter car safety checklist: what to check before the cold
- Winter coats and car seats: why the puffy coat comes off
Sources
Published 7 November 2026 by A.I.T. Multiverse Consulting Ltd, Nicosia, Cyprus. CarsMultiverse is an independent site, not an authority: the advice above is the named official bodies' own, reworded, and their pages are the ones to rely on.