What suould I change first

Tiny
JAMES STAGGS
  • MEMBER
  • 2001 BUICK CENTURY
  • 3.1L
  • 6 CYL
  • FWD
  • 1,800,000 MILES
Need to get it smoged but code reader and smog tech say that it will not pass, code reader say I. Hhave two incomplete sensors egr. And catalyst?What could be wrong
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Wednesday, September 7th, 2016 AT 8:56 PM

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Tiny
CARADIODOC
  • EXPERT
"Change first"? We don't fix cars that way. It sounds like you're trying to say you have two monitors that haven't run. Those are self-tests the Engine Computer performs, but only when a very specific set of conditions are met. Those tests take the place of some of what the people at the test station used to have to do manually. To say that a different way, if a monitor has run and "passed", that's all the tester needs to see to approve your car.

Unfortunately there is a huge variation in what it takes for those tests to run on different car brands, models, and years. Your best bet is to stop in at the dealership and ask at the service desk. The person there might have to enlist the help of one of their mechanics who can tell you what is needed during the "drive cycle". The conditions can include any variation of things like sustained highway speed for at least 20 minutes, a brief burst of wide-open-throttle, an extended period of coasting, and things like that. On a lot of GM vehicles you'll feel a little jerking or surging once in a while when the Engine Computer cycles the EGR valve or the purge valve, and watches the oxygen sensor readings to see if the expected results occurred. Those tests with their barely-noticeable hiccups in engine performance don't occur real often, so if a driver does notice something, it happens so seldom that they dismiss it or ignore it.
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Wednesday, September 7th, 2016 AT 10:02 PM

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