Vehicle emission norms are getting more strict and India is moving towards BS6 Stage 2, meaning cars have to run cleaner. 

The new RDE norms require vehicles to have an on-board self-diagnostic device that will monitor the emissions in the catalytic converter and the O2 sensor. This eliminates lab testing the vehicles.

Smaller diesel engines, mostly the 1.5-litre diesel mills used the Lean NoX Trap technology that is inexpensive. However, to comply with BS6 Phase 2, cars will have to use Selective Catalytic Reduction method, which is expensive.

Also, dwindling sales numbers for diesel vehicles in the hatchback and sedan category does not make sense for carmakers to invest in this new method.

However, for larger diesel engines, 2.0-litre units and above, are ready to be compliant under the new rules.