What is Car Exhaust Diagnostics?
The gas concentrations that are measured in a car exhaust can be used to diagnose problems or faults within the engine or its management system. The difference in exhaust readings between cars with and without catalytic converters is huge.
Note that NOx is only created when an engine is under load. To test for NOx the car must either be driven on the road or use be made of a dynamometer. When using a dynamometer for NOx testing the exhaust gases are extremely hot (the engine is under heavy load and there is no slipstream ventilation) so a high temperature exhaust probe must be used. NOx levels of 3000 to 4000 ppm are common even for new well tuned engines when under load.