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David H
David H, Cadillac Technician
Category: Cadillac
Satisfied Customers: 2677
Experience:  18 years cadillac dealer.ase master master certified
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Cadillac Deville: Diagnostic trouble codes P0171 and P0174

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Diagnostic trouble codes P0171 and P0174 have been registered. These are Fuel Trim System Lean Banks 1 and 2 respectively. If I re-set these, they re-appear the next time I am under heavy load. I presume continued operation under these circumstances will result in engine (ie. valve and/or piston) damage. What are possible causes and solutions?


I would start with a new fuel filter.Also remove the gray engine cover.With the engine idling spray water around the intake manifold pat attention to the area between the throttle body and intake manifold where the rubber plenum boot is.This boot tears and leaks vacuum on all 2001 deville's at some point.To replace the plenum boot requires intake manifold removal and new intake seals as well as the new plenum boot.
Customer: replied 5 years ago.
What am I looking for while spraying the water? Should the idling smooth out? Or am I just looking for the water to disappear into the intake at a leak?
The engine will either start to run very rough or stall out if water hits a vacuum leak.
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