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Unread 07-20-2011, 01:20 PM   #1
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Default 2003 Golf GL 2.0 Catalytic Converter problems

Hey guys,
So my check engine light has been coming on over the past few weeks (Error code P0420), turns out it's front oxygen sensor (?) reading that the catalyst efficiency is below threshold, meaning it's running rich I guess.

Turns out that jettas/golfs 01-04 have catalytic converter problems so it's very possible that this could be a catalytic converter problem but could also just be an oxygen sensor problem.

If I leave it be, no damage to the car but next emissions test I fail.

What would you guys suggest I do?

Much appreciated.
Current Car
2002 WRX Stage 2+ w/ Cobb intake, Cobb EBCS, Mishimoto performance radiator, Cobb 3" downpipe, Greddy Evo2 3" Catback, StopTech slotted rotors & pads, stainless steel brake lines, 17x7.5 Gold BBS
Past: 2005 Volvo S60 R, 2003 VW Golf, 1998 Honda Accord

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Unread 07-20-2011, 02:09 PM   #2
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The rear O2 sensor, the one after the cat, monitors the efficiency of the cat. If it's not doing it's job you get a P0420 code.

The proper fix is to replace the cat, a cheap fix is an O2 spacer.

Oxygen sensor extender spacer HHO HYDROGEN Test Pipe O2 | eBay

Oxygen Sensor Spacers & Isolators

But eventually the cat will become so bad the light will come on again. maybe years down the road.
2003 GMC Envoy 5.3

Last edited by Mr Car Guy; 07-20-2011 at 02:13 PM.

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Unread 01-14-2013, 08:49 PM   #3
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Default code p0420 in golf volgswagen 2003 model gl

chances are is not the catalytic converter...don't swap parts without knowing what caused the don't want to spend more money later...the cause could be the a bad coil is exactly what my volgswagen golf 2003 check engine light was telling me (poo420)...cracks in the coil pack will cause a misfire...gas will not be burned ...then raw gas will pass to exhaust system...then code po420 will set... turn your car engine on... then spray some (use a bottle with sprayer) water on the coil pack.. if you notice sparks coming out around the coil pack or where spark plug boots connect to coil...get the coil pack off the car check it for small cracks...they might be hard to be seen but believe me they are also have a choice to fix the can buy a new coil pack (that's what I did, because my car is still in very good shape) or you can buy some jb weld epoxy from auto parts and apply it to the cracks in the same coil pack...let the epoxy to cure for 24 hrs...this will save you a lot of money...

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