What else can cause the cat code?

[GeorgesBlazah]

Its a 2001 12v. Ive already replaced the rear o2 and that didnt solve it. I also replaced the cat and it didnt fix the problem. Ive also replaced the plugs and wires. I also heard about a computer flash for the early vr6s for this same issue, but I called VW and they said that the flash was applied to my car already. Is there anything else I should be looking at before I drive this thing into a wall?

[nyvwb4]

The P0420 -Catalytic converter system below threshold code- may be Bank1, front O2 sensor, but if youve scanned it already then you'ed know if that one was bad.

Any other codes besides P0420?

[GeorgesBlazah]

No other codes, just the cat one.

[Scotty_2.0]

Cat efficiency codes are either the post-cat o2 sensor or the cat itself. To know for sure you'll need a VAG-COM. Think there's a link in the mk4 FAQ about testing your car and post-cat o2 sensor.

[GeorgesBlazah]

Ive replaced both, thats what makes me angry.

[02GTIFREESKIER]

Have you checked the wiring for the 02 to make sure there is not a break or short in the circuit?

[Den9696]

Use a vag com an check to see if you might have a dirty fuel injector. Use Lucas injection cleaner and see if that helps at all. Could be your fix.

[deadleavesdie]

Maybe an anonymous misfire, not enough to throw a code but enough to have pushed a good amount of fuel in there and clogged it up.

[GeorgesBlazah]

Have you checked the wiring for the 02 to make sure there is not a break or short in the circuit?

I know Im late, but wouldnt that give me an O2 sensor code?

[nyvwb4]

Its a 2001 12v. Ive already replaced the rear o2 and that didnt solve it. I also replaced the cat and it didnt fix the problem. Ive also replaced the plugs and wires. I also heard about a computer flash for the early vr6s for this same issue, but I called VW and they said that the flash was applied to my car already. Is there anything else I should be looking at before I drive this thing into a wall?

assuming everythings stock oem and all the replaced items were new out of the box and no leaks in front of the cat, it might be the pre O2 sensor, maybe...was the code the P0420 you didnt really mention the DTC#

Hows it run, OK? getting 27-28 hwy?

[rivermann50]

99 Jetta VR6 P0420 On my car was the front bank one o2 sensor.

[nyvwb4]

Ill be changeing my front one out tomorrow. Glad to here that a front O2 sensor might fix it (fingers crossed).

Got a OEM Bosch @ Advanced Auto in Rochester for
51.00 after a 10% discount.

[Den9696]

I know Im late, but wouldn't that give me an O2 sensor code?

Did you ever get this resolved. I am having the same exact issue.

[gbagby]

I replaced the front O2 sensor and still get the P0420 code.
I do have 190k though. and haven't replaced my cat. i have replaced the maf sensor. back around 100k. and cleaned it with isopropyl.

[Den9696]

I replaced the front O2 sensor and still get the P0420 code.
I do have 190k though. and haven't replaced my cat. i have replaced the maf sensor. back around 100k. and cleaned it with isopropyl.

I placed and o2 spacer on the post cat o2 and now im all set

[poopsonu]

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