Results are presented for on board sensing of the Gases NO, NO2, SO2 and CO2. The optical fibre sensor was connected downstream of the Diesel Particle Filter (DPF) of a Fiat Croma and the measurements from the optical fibre sensors were recorded simultaneously using high specification reference instrumentation mounted in the boot of the car. In this way the results from the optical fibre sensors and the reference instrumentation could be directly compared. The results from the optical fibre sensors indicate that they are capable of measuring single ppm values of NO, NO2 and SO2 as required by the EURO IV standards and CO2 up to a concentration of 15% which is more than adequate for in car monitoring. The optical fibre sensors therefore performed well when compared to the reference instrumentation in tests conducted on a rolling road and during "free driving" on an urban road. © 2008 Springer-Verlag Berlin Heidelberg.