When did cars stop producing carbon monoxide?

They didn’t. Gasoline and diesel cars still produce some carbon monoxide (CO); what changed is that emissions dropped dramatically starting in the mid‑1970s with the widespread adoption of catalytic converters. Only vehicles with no combustion—such as battery electric cars—have zero tailpipe CO.

From high-CO exhaust to low-CO exhaust

Early, carbureted engines ran rich and emitted large amounts of CO, a toxic, colorless gas formed by incomplete combustion. Beginning in the 1970s, regulations forced automakers to add emissions controls that slashed CO output. Two-way catalytic converters—introduced widely in the United States for the 1975 model year—oxidized CO into carbon dioxide once the catalyst warmed up. In the early 1980s, closed-loop fuel control using oxygen sensors enabled “three‑way” catalysts to run at a precise air–fuel ratio, cutting CO, hydrocarbons, and nitrogen oxides simultaneously. Subsequent generations of engine management, tighter emissions standards, and on‑board diagnostics further reduced CO, especially after warm‑up. Still, any combustion engine can emit hazardous CO at cold start, under rich operation, or if emissions equipment fails.

Key milestones and regulations

The following timeline highlights how and when cars’ CO emissions were dramatically reduced, rather than eliminated.

• 1975 (U.S.): Catalytic converters become standard on most new gasoline cars; unleaded gasoline is required to protect catalysts.
• 1980–1981 (U.S.): Oxygen sensors and closed-loop fuel injection enable three-way catalysts to control CO, HC, and NOx together.
• 1992 (Europe): Euro 1 standard effectively mandates catalytic converters on new gasoline cars across the EU.
• 2000s–2010s: Successive U.S. Tier and EU Euro standards tighten limits; modern powertrains and diagnostics keep CO very low when systems are working properly.
• 2020s: Rapid growth of hybrids and battery electric vehicles; only EVs produce zero tailpipe CO.

These steps converted the industry from high-CO exhaust to low-CO exhaust, but did not eliminate CO from combustion engines.

How much carbon monoxide do modern cars emit?

On standardized test cycles with a warmed catalyst, modern gasoline cars emit very little CO—orders of magnitude less than pre‑1970s vehicles. However, CO spikes at cold start before the catalyst lights off, and any malfunction (rich fuel mixture, misfire, or failed catalyst) can raise CO sharply. Diesel engines generally emit far less CO than gasoline engines because they run lean, but they can still produce CO under certain conditions. Hybrids emit no CO when operating purely on battery power, yet their engines still generate CO when they turn on. Battery electric vehicles have no tailpipe and therefore no tailpipe CO.

What influences a car’s CO output?

Several technical and operational factors determine how much CO a vehicle emits in real use.

1. Engine and catalyst temperature: Cold starts produce the highest CO until the catalyst reaches operating temperature.
2. Catalyst health: A degraded or missing catalytic converter can dramatically increase CO.
3. Fuel/air control: Rich mixtures, misfires, or sensor faults (e.g., oxygen sensor) elevate CO.
4. Vehicle/fuel type: Gasoline typically emits more CO than diesel; CNG is generally low; EVs have none.
5. Ambient conditions and altitude: Cold weather and high altitude can lengthen warm‑up and affect mixture control.

In practice, a well‑maintained modern car emits very little CO after warm‑up, but the same car can emit dangerous levels during cold start or when malfunctioning.

Practical safety takeaways

Because CO remains a risk with combustion engines, basic precautions still apply—even with modern vehicles.

• Never idle a car in an enclosed space (garage, workshop), even with the door open.
• Install carbon monoxide detectors in your home, especially near garages and sleeping areas.
• Maintain the exhaust and emissions systems; address check‑engine lights promptly.
• Be cautious with remote starts and cold‑weather idling; early minutes produce the most CO.
• Remember that hybrids emit CO whenever their engines run; only battery electric vehicles have zero tailpipe CO.

Following these steps minimizes exposure and keeps vehicles operating within their intended low‑emission range.

Summary

Cars did not stop producing carbon monoxide; combustion engines still generate some, notably at cold start or when faulty. What changed—starting in the mid‑1970s with catalytic converters and accelerating through the 1980s and beyond—was a dramatic reduction in CO emissions thanks to catalysts, electronic fuel control, and stringent regulations. Only electric vehicles eliminate tailpipe CO entirely.

Does an idling car produce carbon monoxide?

Cars produce more tailpipe emissions (including hydrocarbons, nitrogen oxides, carbon monoxide, and carbon dioxide) when idling—up to twice as much as when they are in motion.

Do cars still give off carbon monoxide?

Yes, modern cars with internal combustion engines produce some carbon monoxide (CO), but catalytic converters significantly reduce the amount of CO released into the atmosphere by converting it to carbon dioxide. While modern cars are much safer than older models without this technology, carbon monoxide can still accumulate to dangerous levels in enclosed spaces, such as garages, if an engine is running, making it crucial to remove vehicles from these areas immediately after starting them.
 
Why Modern Cars Still Produce CO

• Incomplete Combustion: Opens in new tabCarbon monoxide is a byproduct of incomplete fuel combustion. Even with advanced technology, the process of burning fuel in a car’s engine is not 100% efficient, leading to some CO production. 
• Fuel Burning Engines: Opens in new tabGasoline and diesel engines, which power the majority of cars and trucks, rely on burning fuel and inherently produce CO. 

The Role of the Catalytic Converter

• Reduction Technology: The catalytic converter is a vital component of a vehicle’s exhaust system designed to reduce harmful emissions. 
• Conversion Process: It heats the exhaust gases to a high temperature, converting the dangerous carbon monoxide into less harmful carbon dioxide. 
• Reduced Risk: This technology dramatically lowers the amount of carbon monoxide released by modern cars compared to vehicles from earlier eras that lacked this device. 

Situations Where CO Can Be Dangerous

• Enclosed Spaces: Opens in new tabDespite the effectiveness of catalytic converters, carbon monoxide can still build up to lethal levels in poorly ventilated or enclosed spaces. 
• Running the Engine: Opens in new tabNever leave a car’s engine running in a closed garage. The CO can fill the garage, posing a serious risk to anyone inside. 
• Malfunctioning Exhaust Systems: Opens in new tabA faulty or leaking exhaust system can also allow carbon monoxide to escape into the vehicle’s cabin, creating a dangerous situation. 

Do older cars release more carbon monoxide?

Old cars’ compromised exhaust systems are major sources of carbon monoxide (CO), as they degrade over time, allowing CO gas to enter the cabin.

What happens if you sit in a garage with the car running?

Sitting in a garage with a car running exposes you to carbon monoxide (CO), a colorless, odorless, and deadly gas that can cause headaches, dizziness, nausea, confusion, and eventually loss of consciousness or death. Carbon monoxide builds up quickly in enclosed spaces and is dangerous even if the garage door is open, as fumes can linger and even seep into an attached house. To prevent poisoning, never warm up your car or operate any engine in an enclosed or partially enclosed space; always use well-ventilated outdoor areas and install carbon monoxide detectors in your home and garage. 
Why it’s dangerous

• Carbon Monoxide Poisoning: Car exhaust contains high levels of carbon monoxide, a toxic gas that prevents your blood from absorbing oxygen, leading to a fatal lack of oxygen to the brain and other organs. 
• Rapid Buildup: Even short periods of running an engine in a garage can create dangerous concentrations of carbon monoxide. 
• Myth of Open Doors: The idea that a car is safe in a garage with the door open is false; fumes can still accumulate to dangerous levels, according to this YouTube video. 
• Lingering Danger: Carbon monoxide can remain in a garage at dangerous levels for hours after the car has been shut off. 

Symptoms of CO Poisoning
Symptoms often mimic the flu, making them easy to overlook until the situation is dire. Headache, Dizziness and weakness, Upset stomach and vomiting, Confusion, and Shortness of breath. 
What to do 

• Move Outdoors: Always warm up or run your car in a well-ventilated area, such as outside, away from your home.
• Install Detectors: Install carbon monoxide detectors in your home and garage to provide early warning of dangerous levels.
• Stay Safe in an Emergency: If you suspect a carbon monoxide leak, get to fresh air immediately and call for help.