Can you shed some light on the "monitor requirements"?

Question

My 1999 GMC Suburban has no check engine light (error codes) spent over $600 clearing 6 codes. 3 sensors,replaced plug and hoses. Still wont pass smog because of 3 "monitors" still active. The smog station said to drive 50 miles, and bring back. They always say this, been back many times.

Answer 1

The monitor need to be set once the CK ENG LT gets cleared, when all the monitor set it mean the vehicle has met all the drive criteria. This is usually set within 12 minutes and 1.5 mile of driving if you drive at a set required criteria. The smog place will tell you you need to drive it 50 sometimes a 100 miles they say this this because somewhere within this driving mileage you will meet that criteria. The hard one to set are the catalytic monitor and the EVAP monitor. If the catalytic is holding the monitor back to set . Its is because the ECM needs to see a 2 trip criteria. That means it needs to see a cold start up 1 trip is when the engine is at a cold start up and it is driven. this needs to been done twice. Or the monitor will not set. 2 thing that will hold you back, not doing the 2 trip criteria, or there is a pending code, You need to also have more than 1/4 fuel in the tank this will ensure the EVAP will run.