Carbon Monoxide Leaks in Vehicles (Cabin Air Quality)

Carbon Monoxide Detector, CO Alarm, CO Detector, Low Level CO Detector -

Carbon Monoxide Leaks in Vehicles (Cabin Air Quality)

Carbon monoxide gas entering or leaking into your vehicle may be a real problem. A low level carbon monoxide meter will be able to detect and warn of any carbon monoxide accumulation in your vehicle cabin. Carbon Monoxide in the vehicle may enter via various leakage pathways. Carbon monoxide is produced from the vehicle combustion engine.  We advocate using a portable vehicle CO detector that will alarm at 9ppm and a wall mounted CO detector in your garage to warn when a vehicle has been left running.

Pros

Cons

  • A low level carbon monoxide meter is a good way to determine if your vehicle is leaking and or accumulating in the cabin.
  • The CO detector for the car should alarm at 9ppm since the car has a small volume and CO levels can quickly increase.
  • Carbon monoxide may enter your vehicle if stationary and when moving.
  • A CO meter for the car costs less than $100 that will alarm when dangerous carbon monoxide ppm concentration levels are present.
  • Carbon monoxide ppm concentration in your car may cause headaches and compromise your motor skills.
  • CO gas is tricky to detect as it is odorless.
  • Many deaths and injures occur due to carbon monoxide poisoning in and around vehicles every year. Be cognizant of this danger.
  • Do not use a home CO detector to protect you in a car. Their preset alarm points are too high >70ppm.
  • Do not use the paper dots, chemical color change type of CO indicators either as they offer no audible warning alarm.

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. 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.

car carbon monoxide

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.

carbon monoxide detector for car

It is important to understand that a vehicle HVAC system has two operating modes.

  • 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).
  • 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 car

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.

    carbon monoxide car vehicle

     

    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.

    exhaust carbon monoxide snow car

    Carbon Monoxide Entering with HVAC in Recirculation Mode

    recirculation carbon monoxide climate control leak

    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.
    • 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.

    station wagon effect boat marine carbon monoxide

    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.

    carbon monoxide exhaust leak

    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.

    carbon monoxide in cabin

    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.

    user manual carbon monoxide

    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. 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.

      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
      UL2034 (USA)

      > 70 ppm (60 to 240 minutes)

      > 200 ppm (10 to 50 minutes)

      > 400 ppm (4 to 15 minutes)

      CO Detector Alarming Protocol
      EN 50291:2001 (Europe)

      > 50 ppm (60 to 90 minutes)
      > 100 ppm (10 to 40 minutes)
      > 300 ppm (3 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.

      carbon monoxide in garage

      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.

      vehicle NHTSA carbon monoxide

      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 are at play.

      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.  

      1. 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.
      2. 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.
      3. 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.
      4. 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.
      All in all, do not stick your CO detector or CO sensor at the tailpipe of your vehicle .

        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.

        carbon monoxide tesla

        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’’.

        carbon monoxide poisoning exhaust gas 

        What are the Best Carbon Monoxide Detectors for Vehicle Car Cabins?

        Based on customer reviews and the intended "vehicle" niche application, the best carbon monoxide detector for the vehicle is the Forensics Detector Car CO Detector, which alarms at 9ppm (LED) and 25ppm (Buzzer).
        • 🚗 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.

        What does Carbon Monoxide Smell like in the Car?

        Carbon monoxide is odorless. So when it enters your car cabin, you will have no idea or no indication it is there.
        Hence the importance of using a carbon monoxide meter.

        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.

        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.

        Final Words

        • A low level carbon monoxide meter is a good way to determine if your vehicle is leaking and or accumulating in your car cabin.
        • Carbon monoxide may enter your vehicle if stationary and when moving.
        • CO meters less than $100 can alarm when dangerous carbon monoxide levels are present.
        • Carbon monoxide exposure in your car may be cause you headaches and compromise your motor skills when driving.
        • It is tricky to detect carbon monoxide in the vehicle since it is odorless and can enter via pathways you would not imagine or simply cannot see.
        • Many deaths and injures occur due to carbon monoxide and vehicles every year. Be cognizant of this danger.

        About The Author

        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.

        gas detector expert

        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 having a cold beer. 

        Read more about Forensics Detectors here.

        Email:  drkoz@forensicsdetectors.com
        Phone: +1 424-341-3886


        4 comments

        • HENRIETTA R BORDERS

          My granddaughter drives a Ford Focus. At work with extended lunch hour she ate in her car, windows up with AC on. After lunch she reclined in her seat, set an alarm to return to work, and went to sleep. She awoke confused, said she felt funny, vomited and had a seizure. Co-worker called boss, EMS called and taken to the hospital. Car has been in the auto shop since 2/21/22. Her doctor request a report from shop and so far have not received a report. She was notified today that there is nothing wrong with her car. I am skeptical as he was agitated by the request to check for carbon monoxide getting into the cab and put it off for over 2 months. What should my next step be to assure my granddaughters safety? Another auto shop, fire department, Ford dealership, what remedies do you suggest?

        • Rhonda

          Can a faulty filter under the glovebox be a way for Carbon Monoxide to enter the cab of a vehicle, especially if driving in high volumn traffic areas?

        • Joe Mecca

          Carbon Monoxide buildup in car cabin when shutting down.
          Recently I purchased a Sensorcon Industrial Pro CO meter to check around my house. One day I decided to take it with me as we headed out to lunch and here’s what happened after picking up our food. It was cold outside and we found a place to park and turned off the car. At that point the cabin had 0 PPM after driving around 20 minutes. Once we turned off the car and within 2 minutes (windows closed) our Cabin CO climbed to 36 and eventually peaked at 86 PPM. What the heck, we thought it was the busy rd. We tried this experiment 4 times in different places – busy, not busy and the busy area always climbed to 80’s and teh non busy peaked at 42 PPM. So we tried this experiment in a different car and the results are identical. So here is what I hypothesized is that either a car released lots of CO minutes after it shuts down (cooled catalytic converter) and enters the cabin, or, CO from the outside roads or parking lots is sucked in but not released when windows are closed.
          I’d love to hear opinions and love for others to try this with their windows closed and the car turned off.

        • Gene Williams

          Dear Dr. Los, I purchased a used car Pontiac Gran Prix 2005 4 door, a few months back. I was hospitalized one day driving to work. I’m a healthy 54 year old man. I think I was poisoned by a carbon monoxide leak. What’s the BEST CO detector on the market to detect CO. And would I have a case to sue the car dealership?

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