How to Test a Generator Carbon Monoxide Sensor

Why test the CO sensor

Carbon monoxide is an odorless, colorless and toxic gas that can kill you before you are aware it is present. The U.S. Consumer Product Safety Commission (CPSC) warns that a single portable generator produces as much CO as hundreds of cars and that using a generator indoors can kill within minutes. Because CO is invisible and odorless, the sensor on your generator is your first line of defense against this silent hazard. If the sensor fails, the automatic shutdown may not activate, leaving you and your family exposed to dangerous CO levels. A functional test verifies that the sensor and the shutdown system work as designed.

Voluntary standards such as UL 2201 and PGMA G300 define CO emission rate limits and shutoff levels for portable generators, and the CPSC has proposed a federal safety standard that includes CO shutoff system requirements. These standards exist because the consequences of a failed sensor are severe. Testing your CO sensor regularly is a simple, low-cost way to ensure that the safety system works when you need it most. For more context on what the regulations require, see generator CO sensor requirements.

• A working sensor can shut down the engine in seconds when CO builds up.
• A failed sensor may not trigger the shutdown, leaving deadly CO undetected.
• Regular testing is recommended by safety agencies as part of generator maintenance.

What the test checks

A functional test of a generator CO sensor verifies two things: the sensor's ability to detect elevated carbon monoxide, and the engine's ability to shut down automatically when that detection happens. Most generators with CO sensors have a self-test feature, often a button labeled "Test" on the control panel. Pressing the button simulates a CO reading and should trigger the shutdown sequence. If your generator does not have a test button, the manufacturer's instructions will describe an alternative procedure, such as starting the engine and monitoring the sensor behavior under specific conditions.

The test does not require you to expose yourself or the generator to actual CO. Instead, the self-test exercises the sensor and the solenoid that kills the engine. It is important to perform the test outdoors, away from windows, doors, and vents, because the engine will run briefly during the test and produce real exhaust. The CPSC advises never operating a generator inside a home, garage, basement, or shed, and keeping it outside well away from any opening. Review the generator safety checklist for outdoor use before you begin.

Step-by-step functional test

Before you begin, read the generator owner's manual for the specific test procedure for your model. The following steps are a general guideline based on typical generator designs and safety recommendations from the CPSC and the Centers for Disease Control and Prevention (CDC).

Step 1: Perform the test outdoors, at least 20 feet from any window, door, or vent, with the exhaust facing away from the home. Step 2: Make sure the generator is on a level surface and has enough fuel and oil. Step 3: Start the generator according to the manufacturer's instructions, then let it run for a few minutes to reach normal operating temperature. Step 4: Activate the CO sensor test by pressing the test button on the control panel, or follow the manual's alternative. Step 5: The engine should stop automatically within a short time, usually seconds. Step 6: If the engine does not shut down, turn off the generator manually, do not run it again, and contact a qualified service technician.

• Test outdoors, never in a garage or enclosed space, even with the door open.
• Keep the generator at least 20 feet from any opening to the home.
• Have a battery-operated CO alarm in your home to alert you to any CO entry.
• If the sensor fails, stop using the generator and have it serviced before further use.

When to test

Test your generator CO sensor at least once per season, or before each long outage. If you run the generator monthly as part of an exercise routine, include the sensor test in that routine. The manufacturer may specify a test interval in the manual; follow that guidance. If you have ever dropped or damaged the generator, test the sensor before the next use, because physical shock can damage electronic components.

The CPSC recommends checking the batteries of CO alarms in the home twice a year, such as when you change the clocks. Apply a similar schedule to the generator sensor test, and also check that the sensor's indicator light, if present, is functioning. A sensor that does not respond to the test button may be an early sign of a failing component. For a full maintenance calendar, see generator exercise schedule.

What to do if the sensor fails

If your generator does not shut down when you activate the CO sensor test, do not continue to use the generator. A sensor that fails the functional test cannot be trusted to protect you. Turn off the generator and disconnect it from any loads. Contact the manufacturer's support line or a qualified small-engine repair shop to diagnose and replace the sensor or control module. Do not attempt to bypass the sensor or disable the shutdown system; doing so removes the primary safety feature.

While you wait for service, you can still use the generator if you absolutely must, but only by following all safety rules: operate it outdoors, far from windows, doors, and vents, and have a working CO alarm in the living area. However, the safest course is to stop using the generator until the sensor is repaired. Remember that the CO sensor is a life-saving device, not an optional feature. Adding an external CO alarm can provide extra protection in an emergency.

Beyond the sensor: other CO precautions

The CO sensor on your generator is a backup, not a substitute for safe placement. As the CPSC emphasizes, never run a portable generator indoors, in a garage, basement, crawlspace, or shed, even if doors and windows are open. The engine should be placed outside, at least 20 feet from the home, with the exhaust directed away from any openings. The CDC adds that a battery-operated or battery-backup CO alarm should be used in the home whenever a generator is running.

Even with a functioning sensor, CO can enter the living space through open windows, vents, or if the generator is placed too close. A home CO alarm provides an additional warning. It is also wise to learn the symptoms of CO poisoning, which the CDC lists as headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. If you suspect CO exposure, get to fresh air immediately and call emergency services. For more on placement, see generator CO sensor and placed outdoors. You can also brush up on general generator CO safety to keep the whole family safe.

What to pick for your use

Questions

Do all portable generators have a CO sensor?

No. Newer models, especially those built to voluntary safety standards like UL 2201 or PGMA G300, often include CO detection and automatic shutdown. Check the spec sheet or packaging for a CO sensor mention. The generator guide lists models with and without this feature.

How often should I test the CO sensor on my generator?

At least once per season, or every time you do routine maintenance. If you run the generator monthly, include the test each month. Always test after any physical damage or before an extended outage. You can also tie it to your generator exercise schedule to remember.

What should I do if the test button does not stop the engine?

Stop the generator manually and do not run it again until the sensor is repaired. Contact the manufacturer or a qualified technician. Do not attempt to bypass the sensor.

Can I test the CO sensor by placing the generator near a car exhaust?

No. Do not expose the generator to exhaust from another source. The self-test button or the manufacturer's procedure is the correct way. Running the generator near a car exhaust could create unsafe conditions and may damage the sensor.

Does a CO sensor last the lifetime of the generator?

Sensors are electronic components and can fail over time, similar to CO alarms in a home. Follow the manufacturer's recommended replacement interval, which may be several years. Regular testing helps identify failures early. For more details, see our article on CO sensor requirements.

Is it safe to run a generator with a CO sensor if the test fails?

No. The sensor is a critical safety feature. Running the generator without a working sensor removes your protection against CO poisoning. Stop using the generator and have it serviced. Consider an external CO alarm for extra safety.