To control the Oxides of Nitrogen (NOx), there are only one method is available by Exhaust Gas Re-Circulation (EGR). NOx control system that recycles a small part of the inert exhaust gas back through the intake manifold through EGR valve, to the combustion temperature and this system is called EGR system. OBD-II, systems were designed to maintain low emissions of in use vehicles, including light and medium duty vehicles. As per Environment Protection Agency, (EPA) USA, and CARB standards the failure criteria for the catalyst monitor diagnostic are the following: 1.Linear EGR Flow rate: Abnormal low and high flow rate exceeding the specified low and high flow rate that will result in exceeding any of the applicable FTP x 1.5. 2.EGR system component: Any component of the systems performing outside of the speciation’s that will result in exceeding any of the applicable FTP x 1.5. Enable Linear Flow Diagnostic means, the inputs to Enable linear EGR flow diagnostics are : No fault active on TPS, MAP , vehicle speed, intake air temperature, Idle air control, EGR pintle , Misfire, Transmission and coolant temperature etc. EPA regulations required linear EGR system monitoring to determine if there is a restriction in the exhaust gas recirculation systems. The diagnosis is based on the fact in properly functioning systems, given all other things being constant and normal; there is a direct completion between linear EGR Flow rate and manifold air pressure (MAP) changes.

DR. PORAG KALITA, Ph.D. (Auto. Engg.)."Exhaust Gas Re-Circulation (EGR) and OBD –II: Allocation procedure for the Indian Automobiles". International Journal of Computer Engineering In Research Trends (IJCERT) ,ISSN:2349-7084 ,Vol.2, Issue 06,pp.403-411, June - 2015, URL :https://ijcert.org/ems/ijcert_papers/V2I605.pdf,

[1] Proceeding of SAE International Total Life Cycle Conference & Exposition in Michigan, USA, 2000. 
[2] SAE paper no. 2000-01-1477 by Dr.Porag Kalita, M R S Higher Secondary School, Titabor, Assam, India. 
[3] Seminar On Board Diagnostics – II, by Prof. S. Ganeshan, Oakland University, USA/2000. 
[4] SAE paper No. 2000-01-1417 by Sivanadi Rajadurai and M. Tagomori, USA 
[5] SAE paper No. 2000-01-1476, by Dr. Randolph E, Massachusetts Institute of Technology, USA. 
[6] SAE paper No. 2000-01-1499, by Dr. J.W. Bulkily, University of Michigan, USA. 
[7] Automotive Service Business, Volume I, a Book by Dr. Porag Kalita. 
[8] P. Kalita ( 2006), paper presented at the UGC and ICSSR sponsored National Seminar, R M College, Silchar, Assam, India, Feb 6th to 7th/2006. 
[9] P.Kalita ( 2006) paper presented at N.L College, Assam, India, at Ministry of Environment & Forests , N. Delhi Sponsored nat’l Seminar , January 28th to 29/2006.