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vwnewton
vwnewton, VW Owner,ASE Master and L1 Advanced
Category: VW
Satisfied Customers: 307
Experience:  25 years of VW obsession turned into a job, last 15 years as a VW Tech.
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Trying to fix my 2002 v6 Passat having the dreaded p0171 &

Customer Question

Trying to fix my 2002 v6 Passat having the dreaded p0171 & p0174 codes. Replaced MAF sensor, replace all vacuum lines, replaced pvc and hoses, replaced, air pump and can't find the source of problem, what next 02 sensors, intake gaskets, fuel filter ?
JA: Are you certain it's the fuel pressure sensor that's in need of attention? What about the fuel rail? Have you checked it yet?
Customer: No, I havent
JA: Are you fixing your Passat yourself? What have you tried so far?
Customer: all vaccum lines replaced, new Maf sensor and new air pump
JA: Anything else you want the mechanic to know before I connect you?
Customer: No
Submitted: 8 months ago.
Category: VW
Expert:  Canuck Tech replied 8 months ago.

Hi there

Expert:  Canuck Tech replied 8 months ago.

yes, the dreaded catalyst efficiency codes. How many miles on the car?

Expert:  Canuck Tech replied 8 months ago.

My apologies - fuel system lean...

Expert:  Canuck Tech replied 8 months ago.

Have you smoked the intake to look for vacuum leaks? Have you checked fuel pressure?

Customer: replied 8 months ago.
No
Expert:  Canuck Tech replied 8 months ago.

In a nutshell, the computer is having to tweak the air fuel mixture - adding fule - to compensate for a perceived lean condition. Low fuel pressure and volume can cause this. Extra air via a leaky intake can also cause this. Extra air entering the exhaust close to the upper oxygen sensors can set this code as well. I would be doing some smoke testing in the intake and exhaust before i threw any more parts at it.

Expert:  Canuck Tech replied 8 months ago.

*fuel

Expert:  Canuck Tech replied 8 months ago.

If you put a new MAF in it, you can cross that off the list. A used part... adds another varaible. The AIR pump is only for cold start emissions. If it ran all the time though, it would mess up the signals from the o2 sensors, and could cause these codes...

Expert:  Canuck Tech replied 8 months ago.

Fuel pressure

Vacuum Hose Connected 51psi, engine running

Vacuum Hose Disconnected 58 psi, engine running

Residual Pressure (after 10 minutes) 29 psi