The EGR System tends to get restricted or blocked with carbon after 100,000- 125,000 miles which will cause an emissions test failure for NOX. If the EGR system is equipped with an EGR temperature sensor it will trigger a Check Engine Light for improper EGR flow. The repair is to clean out the EGR passages and the EGR Temperature sensor. Our technicians tell this repair is pretty straight forward and takes about 1-1.5 hours. It is also wise to verify the EGR system components i.e. the Transducer, EGR Valve and VSV Solenoid at this time.Google+
Car Problem Reports
Toyota Tercel Failed Emissions Test Due to Blocked EGR System
Toyota Tercel Problem
Average Mileage: 141,800 mi (76,000 mi - 220,000 mi)
egr system was clogged with carbon. cleaned parts and reinstalled. after a couple of weeks/100 miles, check engine light came on with code 71. i havent managed to get this corrected yet.
Visitor, 1996 Toyota Tercel, 220,000 mi
I have changed the EGR valve