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Codes PO171 & PO174 are both showing on Cadilac Deville DHS 2000

We have just replaced the air flow sencor! We think it may be the oxygen sencor but not sure if it is the up or down air flow sencor. We have rebulit the transmission and replaced the coil pack! There was a misfire on the number 8 cyclender! Replaced all spark plugs! Had more code got them off the light came back on with new codes! On Cadilac Deville DHS 2000 Codes are PO171 & PO174 Thank you!

Vehicle: 2000 Cadilac Deville DHS
asked Feb 18, 2012 by anonymous

1 Answer

Since these are lean codes that are affecting both banks, you need to check for things that are a factor on the banks. Start with fuel pressure, vacuum leaks after the maf sensor. It is not likely an issue iwith the Os sensors as it would indicate both upstream sensors failed at the same time. This is very unlikely. I would start with fuel pressure as a possible cause.
answered Mar 9, 2012 by Carguy1 (2,334 points)

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