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Analysis codes P1491 & P0172 on 2002 Acura MDX

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My CEL came on and remained. Local shop check reflected a temp code P1491-exhaust gas recirculating valve lift insufficient & perm code 0172-system too rich. What does this mean? Incidently, after the check the CEL went out but I am still concerned since a trip is coming up.
(1) Answer
The EGR Valve Lift problem is generally a defective electronic EGR Valve. It is the Sensor on the Valve that goes bad. The P0172 Fuel Trim code is a bit trickier. You will need to inspect the fuel trim numbers. An over-reporting Mass Air Flow Sensor will cause this, but have a good tech verify these issues.