Hallo everyone good day to you
My 430 ls 2004 model showing check engine, trac off and vsc for more than 3 years. Scan tool says p0430 catalyst system efficiancy below threshold bank 2. Lately i checked both catalitic coverter, they where in perfect condition. I am driving the car with no trouble. I need to know what is going on I really love this car. If anyone knows how to fix it I would be greatful.. thanks

 

Could be a bad rear O2 sensor. A scanner with live data would make this easier to diagnose. A cheap "fix" would be installing a O2 sensor spacer on the offending sensor and see it that fixes it.

 

thanks for the quick reply, actually the o2 spacer didnt do any good.. I shall try live data next.

 

90% of the time these codes are for an exhaust leak. I had P0430. Take a leaf blower or reverse a Shop-Vac and put it in the tailpipe, seal it up with a rag. Blow air up the tailpipe (engine not running haha!). Take a spray bottle of soapy water and spray all around right before the catalytic converter and any joints etc in the exhaust. P0430 is the passenger side. When you see it blowing bubbles, you found your leak. Mine leaked a tiny amount out of the downstream oxygen sensor, i just removed it and put a dab of copper sealant on it and put it back. Then real leak was the pipe at the fitting right before that. $5 worth of high temp muffler sealant for the win. Been 6 months, no P0430. I've heard many people have to replace the Y-pipe or get it welded up. The live data on my scanner clearly showed the problem, but it is the downstream oxygen sensor being fooled because the leak is sucking in more oxygen than should be there.

 

Most common cause is a crack/split in the exhaust system between the primary CAT and the secondary O2 Sensor.
Mine was left side (P0420) and was caused by a crack in the weld on the flange that attaches the Y-pipe to the primary CAT.
As Treehan says it can also be cause by a leak from the O2 sensor or a leak from between the Y-pipe flange and the CAT flange.

 

update
Sorry for delay
I end up installing L shape spacer to oxygen sensors.. worning signs disapeared thankfully...
thanks to everyone tried to solve my issue, i hope you the best

 

Do you or anyone else have any more information on exactly what spacer you used? Maybe an old email receipt or something? I know if you do the wrong one it can pop a different code due to it not getting enough air to the sensor. TIA!

 

I just want to say thank you. I had the P0430 code and was going to try a spacer or replace my O2 sensor until I found this thread. I just hooked a leaf blower to my tailpipe and plugged the other one with a rag. It was super easy to find the leak just feeling for the air. My problem ended up being a tiny pinhole crack in the exhaust pipe just under the heat shielding clamp downstream of the O2 sensor. Likely from rubbing over time. I just removed the clamp, peeled back some of the shielding, and cleaned the area with a wire brush. Fixed with a $5 roll of exhaust repair tape.