Carbon monoxide (CO) is a dangerous gas that can leach into your vehicle's cabin, posing a severe health risk. To protect yourself and your passengers, it is crucial to use a low-level carbon monoxide meter specifically designed for vehicles. These portable CO detectors can alert you to the presence of carbon monoxide at concentrations as low as 9 parts per million (ppm), ensuring early detection of any potential leaks. Carbon monoxide typically enters the vehicle through various leakage pathways from the combustion engine, making it essential to monitor CO levels continuously while driving. By utilizing a sensitive and reliable vehicle CO detector, you can take proactive steps to maintain a safe environment inside your car and prevent the potentially deadly consequences of carbon monoxide exposure.
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Best Carbon Monoxide Detector for a Car?
- 🚗 USES: Exhaust leaks in vehicles (i.e. SUVs, aircraft, school buses, trucks & fleet vehicles that triggers headaches, nausea & driver fatigue.
- 🔬ACCURATE: CO low-level alarm at 9ppm & 25ppm alarms WHO, EPA, ASHRAE, OSHA, NIOSH CO recommended exposure levels.
- 🔔 FAST ALARMS: Alarms at >9ppm @ 60 secs, compared to home CO detectors that only alarm >70ppm @ 60-240 minutes. Bright RED LED and buzzer alarms.
Can You Get Carbon Monoxide Poisoning While Driving Your Car?
Yes you can.
There are various ways the carbon monoxide can enter the vehicle. Generally speaking, carbon monoxide is produced by your engine, and may find its way into your vehicle either when your vehicle is stationary or moving.
Why is it Dangerous to Breath Carbon Monoxide Whilst Driving?
Being exposed to carbon monoxide whilst driving will impair your motor skills, reflex time and hand-eye coordination - increasing your risk of a collision.
What Is Considered a Low Level Carbon Monoxide?
Carbon Monoxide less than 50 ppm is considered as a low level of CO concentration. Depending on who you ask, this definition may change or vary. Although it is termed "low level," these CO concentrations can still be dangerous especially when driving.
Symptoms of low levels of CO exposure include:
- Mild headache
- Mild nausea
- Shortness of breath
- Compromised motor skills
Can Cars Release Carbon Monoxide?
Yes they can.
Combustion engines burn fossil fuel (gasoline) and then produce emissions such as carbon monoxide (see a real car exhaust demo here undertaken with a Carbon Mononxide Exhaust Gas Analyzer). Even with a functioning catalytic converter, carbon monoxide is still released from the exhaust of the vehicle.
The amount of carbon monoxide release from the vehicle increases when:
- Acceleration or Loading can easily generate over 1000ppm carbon monoxide tailpipe emissions - even when a catalytic converter is present.
- Catalytic converter is compromised (life and temperature).
- Dynamic driving situations where the vehicle engine management system cannot maintain an optimal air fuel ratio and hence producing inefficient combustion and higher than normal carbon monoxide emissions.
How Does Carbon Monoxide Enter the Vehicle?
There are various ways carbon monoxide can leak into your vehicle.
The most common method of carbon monoxide entering the car is via the HVAC system, sometimes referred to as the climate control system. The HVAC is the Heating, ventilation, and air conditioning that is designed to provide comfort to passengers. One can control the temperature, A/C, heating and speed of the fan including if air is to enter from the outdoors (Fresh Air) or be recycled (i.e. use the supply air from within the vehicle cabin).
A typical climate control panel in a car is shown below - notice the recycle button.
It is important to understand that a vehicle HVAC system has two operating modes.
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Recirculation OFF (Fresh Air Mode)
- When the Fresh Air Mode is enabled and the fan is blowing, a positive pressure exists in the car cabin so it is less likely that outside air enters the cabin compartment through leaks or any "unintended" pathways. It will enter only from the fresh air intake that resides below the front windshield (in a typical vehicle).
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Recirculation ON (Recycle Mode)
- In the recirculation mode, the recirculation door shuts the fresh air intake path so that only cabin air circulates. Such a function helps eliminate external dust or pollution for increased passenger comfort.
Carbon Monoxide Entering with HVAC Fresh Air Mode in Motion
Carbon Monoxide can enter the cabin in fresh air mode as follows:
- Air enters the front of the vehicle and then air leaves the vehicle cabin through the air-relief valves or through uncontrolled leak paths, which are generally a result of unintentional gaps in the vehicle body.
- Relief valves (air extractors) are usually placed in the trunk areas and employ one-way, self-closing flaps that open only when there is a positive pressure differential between the cabin interior and exterior.
- Carbon Monoxide may enter the cabin if:
- the outdoor air contains carbon monoxide due to heavy traffic or a polluted vehicle in the direct path of yours
- carbon monoxide leaks from the exhaust, exhaust manifold and engine bay
- carbon monoxide accumulates in a quasi indoor environment such as a parking structure or garage and is drawn into the cabin via the fresh intake vent
Carbon Monoxide Entering with HVAC Fresh Air Mode Stationary
Polluted air may enter the vehicle via the HVAC system in fresh air mode. Air may be sucked into the vehicle by the blower - intake is usually passenger side under the windscreen.
If the vehicle is stationary is may draw in polluted air. Dangerous scenarios when stationary include:
- Parked and engine is on. Downwind direction from exhaust to HVAC intake can draw exhaust gas into the cabin.
- Parked and engine is on in a quasi indoor environment with poor ventilation such as a parking structure, garage, or home garage. In this case, exhaust gas and carbon monoxide does not dilute with the outdoor environment and can be drawn into the vehicle cabin.
- Neighboring station vehicle emits pollution and is drawn directly into the cabin.
- Parked and engine is on. Obstructions such as snow or debris can redirect the emissions back into the vehicle.
Carbon Monoxide Entering with HVAC in Recirculation Mode
When a vehicle is in motion, a pressure differential occurs between the exterior rear and the cabin. It works like this:
- The surface pressure is higher at the rear of the vehicle than the internal cabin. For those interested, the pressure difference may be up to 0.5 inH2O at freeway speeds.
- As the vehicle moves, it pushes the air to make way for its motion. At the rear of the vehicle, it abruptly ends, creating a void where a low-pressure “near-wake” region forms.
- The cabin has even less pressure than the rear of the vehicle.
- The faster the vehicle travels, the higher the pressure differential between the cabin and the rear of the vehicle.
- Exhaust components mix with eddies (swirling air) in the near wake region and if any leaks exist in the rear vehicle surface, polluted air will be drawn into the cabin.
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In the recirculation mode, and whilst in motion, cabin pressure is less than the rear of the vehicle. If any leaks exist, exhaust gases mixed with external air will be drawn & leak into the cabin.
The phenomena of carbon monoxide from the exhaust coming into the vehicle in this fashion is sometimes referred to as the station wagon effect and also occur when a boat is moving.
Can an Exhaust Leak be the cause of Carbon Monoxide Entering the Car?
Yes it can.
If there is an exhaust leak in your engine bay or under the vehicle, the gases can easily mediate through any openings or orifices and enter the vehicle.
If the leak is in the engine bay due to a cracked exhaust manifold or exhaust leak, exhaust gases such as carbon monoxide can enter via the engine bay into the vehicle, or directly be drawn into the intake vent via a compromised rubber hood engine bay seal.
Can Carbon Monoxide Enter the Cabin from the Trunk of the Vehicle?
Indeed it can.
To get a better grip of how this may happen see the animation below.
- When the HVAC is in recirculation mode and as the vehicle travels, a pressure differential between the cabin and the rear of the vehicle is produced.
- Exhaust components mix with eddies (swirling air) in the near wake region and if any leaks exist in the rear vehicle surface, polluted air will be drawn into the cabin.
This is also a simulation shown below.
This phenomena is well known and not controversial as it is warned against in most automotive user manuals. Text like the example below can be readily found. This is a real problem hence we recommend to follow this advice and never drive a vehicle with the trunk lid or rear tailgate open.
Can You Get Carbon Monoxide from Sitting or Sleeping in Your Car?
Yes you can.
Do not sleep in your vehicle with the engine running. Also do not sit in your car as sitting will prolong the time you are exposed to carbon monoxide in your car gas chamber. In addition, do not run the engine and sit in your car for long periods of time.
Unknowingly, carbon monoxide may enter and accumulate within your vehicle cabin as it has done to many that have died from sleeping in their vehicle due to carbon monoxide poisoning.
When stationary, Carbon Monoxide may build up around the vehicle, be redirected or obstructed back into the vehicle and accumulate within the vehicle. Debris, snow or exhaust redirected to the HVAC intake may direct dangerous carbon monoxide into your vehicle. Deaths occur in this fashion every year, so be very cautious.
Can Carbon Monoxide Enter from Another Vehicle?
Yes it can. Below is a photo I took (Dr. Koz) when I was stopped at a set of traffic lights and an old truck pulled up next to me. I was not happy!
Carbon Monoxide can infiltrate your vehicle when another car or truck stops beside you. This is especially concerning if their exhaust pipes are directed towards the side of your car. This happens at traffic lights or in congested start stop traffic jams. It can be frustrating when trucks or vehicles with strong emissions stop next to you, as their exhaust fumes may enter your vehicle. This situation is extremely hazardous and should be avoided. To stay safe, either position your car ahead or behind the emitting vehicle and keep your windows rolled up.
Please exercise caution. If you suspect that exhaust fumes have entered your car from a nearby parked vehicle and you decide to close the windows, it's essential to know that you haven't made the situation safe. By doing so, you may have trapped the carbon monoxide toxic gas inside the cabin. Therefore, once you resume driving, make sure to obtain fresh air by properly ventilating the vehicle.
What Are Dangerous Levels of Carbon Monoxide in My Vehicle?
No standards for CO have been decided for the air within your vehicle. It can get confusing since various agencies and organizations have different recommended exposure levels. There are some guidelines that can be extrapolated for personal safety. Below is a table that summarizes the carbon monoxide exposure:
Agency |
Limits |
WORLD HEALTH ORGANIZATION (WHO) |
9 ppm average over 8 hours |
ENVIRONMENTAL PROTECTION AGENCY (EPA) |
9 ppm average over 8 hours |
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) |
9 ppm average over 8 hours |
National Institute for Occupational Safety and Health (NIOSH) |
35 ppm average over 10 hours 200 ppm ceiling value |
Occupational Safety and Health Administration (OSHA) |
50 ppm average over 8 hours |
American Conference of Governmental Industrial Hygienists (ACGIH) |
25 ppm average over 8 hours |
CO Detector Alarming Protocol
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> 70 ppm (60 to 240 minutes) > 200 ppm (10 to 50 minutes) > 400 ppm (4 to 15 minutes) |
CO Detector Alarming Protocol
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> 50 ppm (60 to 90 minutes) |
Forensics Low Level Carbon Monoxide Detector |
> 25 ppm (1 minute) |
Is it Dangerous to Park my Car in the Garage?
Yes it is.
Deaths occur annually from carbon monoxide poisoning due to vehicles left accidentally running in home garages. Problems have occurred with:
- elderly forgetting their engine on
- vehicles with keyfob start/stop confusion
- hybrid vehicles left ON due to confusion if engine is on/off
Also, do not back up your vehicle into the garage, this may also create carbon monoxide accumulation in the garage and or attached home.
Good news is that some manufacturers are implementing "idle times" to switch off engines left running to reduce this risk.
Which Cars Leak Carbon Monoxide?
Nobody really knows until carbon monoxide tests are performed.
However, checking the NHTSA website and performing a "carbon monoxide" keyword search to review complaints can give you some insight. Some vehicle models and brands that have made nation news regarding carbon monoxide concerns include:
Dr. Koz did undertake an analysis and collated data from the NHTSA keyword search 2013-2019 that identify carbon monoxide incidents/complaints with various automobile makes and suspected defects. The results are in the below table.
How do you Know if you Have a Carbon Monoxide Leak in Your Car?
A tell tale sign of carbon monoxide poisoning may be headaches or nausea whilst driving (it is for me). To confirm, we recommend using a low level CO meter to confirm any carbon monoxide accumulation.
Do not use a generic "home" CO detectors as their pre-set alarm thresholds are too high. They alarm at 70ppm and those with displays start showing displaying CO levels only above 30ppm.
To determine how CO leaks into the car is not trivial. There are many technical methods and protocols Dr. Koz has developed to determine how CO enters a vehicle. In general however, finding carbon monoxide leakage paths into a vehicle may be obvious (visually) or may require additional physical techniques to identify.
Can Car Exhaust Set Off a Carbon Monoxide Detector?
It may or it may not. Many factors exist.
To properly test your CO meter or detector with household items, follow our recommended CO test procedure.
When somebody sticks their CO detector direct to the tail pipe of their exhaust there are many "bad" things occur that the lay man may not be considering.
- The carbon monoxide concentration is NOT constant. Exhaust gas varies in CO level. Sometimes it is low and sometimes it is high. When it exits the tail pipe, it quickly dilutes with atmospheric air, and may further be manipulated by a cross-wind.
- It has a large amount of humidity and is expelled at a high temperature. The combination of high temperature and humidity will likely damage the CO sensor and present a false reading or alter the CO sensor calibration, making it inaccurate for further use.
- The high content of humidity in the exahust will create a "false positive" to the CO detector. In other words, high humidity will make the CO sensor react as if it is actually reading carbon monoxide.
- The exhaust gas has acidic gas components such as NOx that cancel the real CO sensor output. Special filters are needed to remove humidity, treat acidic gases, and condition the exhaust stream before it is exposed to the gas sensor of your CO detector. Furthermore, the acidic gas itself may permanently poison the CO sensor element.
Do Cars Have Carbon Monoxide Sensors?
Air quality sensors that detect noxious exhaust gases such as Carbon Monoxide are commonly found in some vehicles made by General Motors, Volvo, Ford, Nissan, BMW and Mercedes. In fact, Tesla has a carbon monoxide sensor in their Model S and X.
These sensors systems are typically supplied by OEM component and system supplies such as Delphi (Germany), Valeo (France) and Sensata (Netherlands). Specifically, these “air quality sensors”, sometimes known as “air quality systems”, “air quality monitors” are physically incorporated within Heating, Ventilation and Air Conditioning (HVAC) systems and most often marketed as a “comfort feature” where, based on the sensors’ gas concentration reading, will trigger a ventilation flap mode change, either recirculation or fresh air mode, in order to minimize ambient noxious gases from entering the car cabin, and ultimately, increasing the “comfort” of vehicle occupants.
It is not far fetched these same sensors can be engineered to also warn when CO levels within the cabin are on the rise. Such systems have been proposed, by Dr. Koz, however yet to be factory implemented by vehicle manufacturers. Until then, it is best to rely on an aftermarket CO detector for your vehicle.
Is Suicide a Problem in Vehicles due to Carbon Monoxide Poisoning?
Unfortunately yes it is and has been a big problem for decades.
When Bogart found Hepburn trying to commit suicide via exhaust gas in the 1954 movie Sabrina, awareness of carbon monoxide (CO) poisoning dangers were still at their infancy. During the same year, a correspondence letter sent by Mr J. Hynes published in the British Medical Journal stated1 ‘‘I am wondering how many non-fatal CO poisoning are occurring...the practice of heating bedroom by means of portable paraffin heaters is common...the gas cooker may also be a source of slow poison to the unsuspecting housewife’’.
What does Carbon Monoxide Smell like in the Car?
Is Carbon Monoxide poisoning a Problem for Trucking, RVs, Campers, Buses and Big Rigs?
Yes it is.
Vehicles that are designed to "sleep" occupants are extremely dangerous. Sleeping in confined spaces such as a camper, truck or RV whilst having a generator of engine operating is dangerous and the more reason to have a working CO detector. Precarious situations include:
- RVs and Campers: Extra dangerous since they have multiple carbon monoxide sources such as generators, propane appliances or may be parked close to neighboring generator exhausts.
- Trucking Big Rigs: truckers both drive and sleep in their trucks, spending so much time allows even the smallest carbon monoxide leak to accumulate from a portable heater, engine leak or generator leak.
- Buses: Older school buses have a high likelihood of leaking exhaust into the bus. Poor maintenance and inspection (due to funding and cost savings) result in poorly operated school buses.
Can Carbon Monoxide enter a School Bus?
Yes.
There are many reports of kids being sick due to carbon monoxide entering a school bus. There are several ways that CO can enter a school bus:
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Exhaust from other vehicles: If the school bus is in traffic or parked near other vehicles with running engines, exhaust fumes containing CO can enter the bus through open windows, doors, or vents.
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Malfunctioning exhaust systems: If the school bus's own exhaust system is not functioning properly, CO can build up inside the bus.
Advice for Carbon Monoxide Detectors for Cars?
- Do not use the paper dots, chemical color change type of CO detectors either as they offer no audible warning alarm.
- Do not use a standard "home" CO Detector, they are not sensitive enough.
- Place the CO detector in line of sight, so you can view the digital display when driving. Its install location regarding height is not a concern, most important is to see it and hear it.
- Carbon monoxide may enter the vehicle via the trunk. A good idea is to undertake a test by placing a CO detector in the trunk. After a test drive for 15 minutes, open the trunk and inspect the carbon monoxide meter readings (typically when HVAC is in recycle mode).
- Do not use the paper dots, chemical color change type of CO detectors either as they offer no audible warning alarm.
- Do not back up your vehicle (exhaust) first in your garage. Also, do not "warm up" your car in a garage.
- Do not use a CO2 detector. We are talking about a CO detector. Dont get CO2 and CO confused, they are totally different gases. CO is much more dangerous.
Can You Detect Carbon Monoxide Leaks From Vehicle Exhaust Systems Through Smell?
No, carbon monoxide from vehicle exhaust leaks cannot be detected by smell. It remains odorless regardless of its source, making mechanical inspection and CO detectors essential for safety.
Do Cars Produce Carbon Monoxide?
Because vehicles have catalytic converters, most people think cars do not produce carbon monoxide gas. This is false. It is indeed true that catalytic converters reduce toxic gas emission, but they do not eliminate it. Situations such as high RPM, vehicle under load and a vehicle restricted of oxygen, say running in a closed garage with depleted oxygen, are situations where the carbon monoxide emission can be extremely high and deadly.
Do Cars Emit Carbon Monoxide or Carbon Dioxide?
Cars emit carbon monoxide (CO) and carbon dioxide (CO2). Carbon monoxide is a toxic gas that can be harmful to humans in high concentrations, while carbon dioxide is a greenhouse gas that contributes to climate change.
Exhaust Gas Emissions from Cars
California OSHA regulations limit emissions to 1.5 percent CO for the larger engines (above 140 cubic engines), with higher limits for smaller engines.
Standards for Internal Combustion Engine Exhaust Emissions
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Engine displacement in Cubic Inches |
Carbon Monoxide (CO) Concentration %vol / (ppm) |
| 50-100 |
2.3%vol (23,000ppm) |
| 100-140 | 2.0 %vol (20,000ppm) |
| 140 or greater |
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Final Words
About The AuthorDr. Kos Galatsis ("Dr.Koz") is the President of FORENSICS DETECTORS, where the company operates from the scenic Palos Verdes Peninsula in Los Angeles, California. He is a subject matter expert on gas sensor technology, gas detectors, gas meters, and gas analyzers. He has been designing, building, manufacturing and testing toxic gas detection systems for over 20 years. 
Every day is a blessing for Dr. Koz. He loves to help customers solve their unique problems. Dr. Koz also loves spending time with his wife and his three children going to the beach, grilling burgers, and enjoying the outdoors. Read more about Forensics Detectors here. Email: drkoz@forensicsdetectors.com |