SIAM is the Apex National Body representing Indian Automobile Industry

In-use Vehicle Norms

Petrol/CNG/LPG Driven Vehicles



Measured at idling:

Vehicle Type CO (%) *HC (ppm)
2&3 wheelers (2/4 stroke) (vehicles manufactured before 31/3/2000) 4.5 9,000
2&3 wheelers (2 stroke) (vehicles manufactured after 31/3/2000) 3.5 6,000
2&3 wheelers (4 stroke) (vehicles manufactured after 31/3/2000) 3.5 4,500
Bharat Stage -II compliant four wheelers 0.5 750
Four wheelers other than Bharat Stage -II compliant 3.0 1,500

Four Wheelers BS IV               Low Idle                                                                                                                                         0.3                 200

                                                High Idle   ( Lambda @ 2500 +/- 200 rpm : 1+/- 0.3 or as per manf. specification)                       0.2                 

* For CNG & LPG vehicles the measured hydrocarbon value shall be converted using the following formula and then compared with the limits
· For CNG Vehicles- non methane hydrocarbon, NMHC = 0.3 X HC

· For LPG Vehicles- reactive hydrocarbon, RHC = 0.5 X HC


Diesel Vehicles


Free Acceleration Smoke Test

Method of Test Maximum Smoke Density
Light Absorption Coefficient (1/m) Hartidge Units

Free Acceleration Test for Turbo Charged engine and Naturally aspirated engine

Free Acceleration Test for BS IV vehicles                                            







  1. Test should be done at authorised Pollution Check Centers
  2. Test should be done every six months or as per the directions of the State Government
  3. No vehicle shall ply in the country without a valid pollution under control certificate
  4. BS IV Vehicles : Test to be done once in a year