This paper describes an optical fibre based system suitable for monitoring the presence of carbon dioxide in the exhaust system of a motor vehicle. Conventional automotive pollution sensors fail to meet monitoring requirements as specified by the European Commission for various reasons. The sensor was designed using low cost and compact mid-infrared components, which make it suitable for insertion into a vehicle. The response of the sensor to carbon dioxide supplied from a cylinder in the laboratory is presented. In addition results taken in-situ in an exhaust of a Fiat Croma diesel engine are presented. ©2008 IEEE.