2001 golf gti had fault code p0420 come up had new rear lamda done still p0420 so got new front lamda, code still come up so then got a new cat, then fault code p0420 and p0120 come up,, then had new maf sencor,, still now im getting fault code p0420 come up please help

Can't by pass as oxygen sensors control your fuel

I suspect your exhaust converter has failed & the car has
been running rich for years & ruined it

Wouldn't your repair guy be able to solve all your issues,
after all you were at a shop for some work

Sounds like they sold some service instead of diagnosing
the reason you were there

Hello: Code 420 normally indicates a catalytic converter is operating below 60% efficiency. You need to take your car to another shop and request a COMPLETE diagnosis not a dart board guess.

1993-2005 Volkswagen Jetta, Golf, GTI, Cabrio (A3-A4) Hatchback & Sedan Workshop Repair Service Manual - 350MB PDF

1993 2005 Volkswagen Jetta Golf GTI Cabrio A3 A4 Hatchback Sedan...

This is a COMPLETE Service and Repair Manual for your 1993 1994 1955 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 VW Jetta, Golf, GTI, Cabrio (1.8L turbo, 1.9L TDI and PD diesel 2.0L gasoline, 2.8 LVR6) (A3, A4 Platform) Hatchback & Sedan. It covers every single detail. All models, and all engines are included.

This QUALITY manual is 100 percents COMPLETE and INTACT, no MISSING/CORRUPT pages/sections to freak you out! Detailed illustrations, exploded diagrams, drawings and photos guide you through every service repair procedure. This manual can be viewed on any computer, as well as zoomed and printed. All repair procedures are covered A-Z. This manual for VW Jetta, Golf, GTI, Cabrio makes any repair job easy to do with very easy to follow step-by-step instructions & pictures on all areas of repair.

1993 1994 1955 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 VW Jetta, Golf, GTI, Cabrio (1.8L turbo, 1.9L TDI and PD diesel 2.0L gasoline, 2.8 LVR6) (A3, A4 Platform) Hatchback & Sedan
===========
Format: PDF
System: All Versions of Windows, Mac, iOS, BB, Android, etc..
Requirements: PDF Reader.
Printable: Yes

TABLE OF CONTENT (example)

GENERAL INFORMATION *

ENGINE *
engine mechanical
engine lubrication system
engine cooling system
engine control system
fuel system
exhaust system

TRANSMISSION/TRANSAXLE *
clutch
manual transaxle
automatic transaxle

DRIVELINE/AXLE *
front axle
rear axle

SUSPENSION *
front suspension
rear suspension
road wheels & tyres

BRAKES *
brake system
parking brake system
brake control system

STEERING *
power steering system
steering system

RESTRAINTS *
seat belts
supplemental restraint system (srs)

BODY *
body, lock & security system
glasses, window system & mirrors
roof
exterior & Interior
Instrumental panel
seat

AIR CONDITIONER *
air conditioner system

ELECTRICAL *
wiring diagrams
starting & charging system
lighting system
driver information system
wiper, washer & horn
body control system
lan system
audio visual, navigation & telephone system
auto cruise control system
power supply, ground & circuit elements

MAINTENANCE *
maintenance

INDEX *
alphabetical Index

1993 1994 1955 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 VW Jetta, Golf, GTI, Cabrio (1.8L turbo, 1.9L TDI and PD diesel 2.0L gasoline, 2.8 LVR6) (A3, A4 Platform) Hatchback & Sedan

i would renew trhe pair of them to be honest ,and if that didnt clear the emmisions then a new cat as well

Diagnostic code produces P0420 catalyst system efficiency below threshold-Bank 1. Probable causes are listed as follows:
1-air leak in exhaust before rear 02 sensor, 3-Fuel system fault,
4-faulty catalytic converter.

PO420 code is for catalyst system efficiency below threshold (bank 1) Usually it means that it is time for a new catalytic converter on bank number 1. Cylinder bank number 1 is always the bank with the number 1 spark plug in it.

it is probably your door lock has gone into safe mode.you need a new door lock.try using the lock/unlock button on your remote or on the drivers door button and gently tap the door handle with your hand while pressing the lock/unlock button,carefull not to dent your car.if that does not work,try disconnecting the cars battery for a few minutes,but note the vehicle might pick up fault codes which need a diagnostic machine to clear...good luck

what about after 5 minutes of driving

try this site:
http://www.obd-codes.com/p0420

ive bought a cat back scorpion exhaust for my mk4 2.0 golf gti the problem is its banging off the bottom off the car witch is doing my nut in i bought a 4motion rear valance for the cut out for the tail pipe witch was a waist of time as the exhaust is no where near the cut out as it will not go any higher because its already hitting the body does any one else have this problem your advice on this would be helpfull thanks