Abstract: A vehicle carbon monoxide detection system 10 including internal 20 and external 40 carbon monoxide sensors operatively associated with the vehicle cab 150 and connected to a computer 60 that will selectively activate one of the sensors 20, 40 in response to the output of the vehicle speedometer 100. When the selected sensor 20, 40 detects excess carbon monoxide fumes relative to the vehicle cab 150, the computer will deactivate the vehicle ignition switch 110 stopping the vehicle motor 120 which is the source of the carbon monoxide fumes.