P0420 code

**VTR99** · 08-21-2007, 03:51 PM

Just bought my WS6 with only 10,000 miles, and on the trip home I get a check engine light. The code is P0420 -- Catalytic efficiency below threshold (Bank 1). I already took it to my local shop, and had the Pontiac dealer look at it. Both said almost immediately that I would need a new catalytic converter. My question for the list experts is which O2 sensor is bank 1? Is it driver's side, or passenger side? I figure it only makes sense to check the sensor before letting them dick up my exhaust system.

**SeVeReDiStOrTiOn** · 08-21-2007, 04:46 PM

Bank 1 is the drivers side and the post cat sensor is sensor 2.

There's also a federal emissions warranty that's good up to 80,000mi...but that doesn't matter because you only have 10,000mi on the clock and GM extended the cat warranty to 120,000mi.

The pontiac dealer should've replaced it right there on the spot...I dunno why they didn't unless they're just being pricks.

**VTR99** · 08-21-2007, 05:08 PM

Thanks for the info... Any chance it's just a bad O2 sensor? Seems pretty strange the cat would go bad after only 10k miles...

**SeVeReDiStOrTiOn** · 08-25-2007, 10:30 AM

Yea it's possible...try swapping the driver side o2 with the passenger side...if you get a p0430 code (passenger side low efficency code) you know it's the o2.

**jag42420** · 08-25-2007, 01:44 PM

I'd let the dealer figure it out. New cat + labor = free ( http://www.ls1.com/forums/showthread.php?t=35957 ). If that doesn't fix it, then you'll know it's the sensor. The cats on these cars have been known to fail anywhere from 5k-130k miles. Could very well be the problem. I wouldn't waste my time.

**truckguy** · 09-08-2007, 02:16 PM

my wife's 2001 firebird is throwing a 420 code also. it has 84,000 miles and i changed the cat. still throwing the code. i was wondering if you changed the o2 sensor, and if so, did that fix the problem? thanks, ryan.

**2001NBMZ28** · 09-08-2007, 02:51 PM

GM extended the stock cat warranty on the LS1 00-02 F cars last December to 10 yrs/120K - even reimburse you if you had it replaced earlier. Rarely is P0420 the sensor if installed correctly and keeps coming back.

**truckguy** · 09-08-2007, 02:53 PM

why would it come back then if i already changed the cat?

**2001NBMZ28** · 09-08-2007, 03:19 PM

It won't go off immediately unless you clear it, assuming it's been changed for a while? Dunno. See www.gearchatter.com/viewtopic9138.php

**truckguy** · 09-11-2007, 04:16 PM

it was changed on sept 1st. light was still on and i reset it by pulling the negative cable on the battery. this lasted for two days. light is back on now. this is a v6. i don't know if that makes a difference or not.

**jag42420** · 09-12-2007, 04:11 AM

Go to Autozone and have them delete it with a handheld. I don't think removing the battery cable actually deletes a code on the OBDII system like it did the OBDI.

Just a thought. Did you replace the converter with an OBDII compatible one? Some of the cheaper ones don't do well and can set codes.

**truckguy** · 09-12-2007, 03:08 PM

i bought the one autozone's computer said was for the car. although it was not the most expensive one. i just had autozone reset the light. we'll see if it comes back. thanks for the help.