Vettehappy

Hello again,

I need some help and advice on my 96 LT1 Auto Coupe. SES Light is on and I have a DTC P0420 Which is TWC System Low Efficiency Bank 1.
Per the FSM I have checked for exhaust leaks and HOS wiring and connections, all seems good. Next step per FSM is to change TWC.
My questions are; Code was set after 1/4 tank of Chevron super premium, could this have anything to do with it? I have since run through severa tanks of Chevron mid range, no effect; Also if I do need to change the TWC, should I change both? Also what replacement would you recommend?
Any ideas would be welcome.
Thanks in advance.

LouisvilleLT4

I have a '96 as well. Changing your TWCs is a pain. I have made several posts/threads about it so search for them. If your TWCs are clogged, you should notice pinging sounds and hesitation when you floor it in high gear at low rpm (oh wait, just noticed you have a friggin slushbox so I guess you can't try this without your nanny transmission downshifting for you, ha ha, that sucks.).

If this is not the case, it was probably just bad gas as you said. Go to autozone and make them clear the codes out once all that gas is out of the system, and see if the code comes back. I bet it won't.

Vettehappy

Thanks for the quick reply, I have already cleared the code and it's back, even took it on a highway 300 mile trip yesterday, but no luck.

toptechx6

OBDII cars use the downstream O2 sensors to monitor cat function, slower cross counts compared to the upstream indicate a good cat. If your scan tool will monitor the sensor in question see what it is doing.
Personally, I would try a new sensor before buying a cat simply from the cost/benefit standpoint
You don't say how many miles you have, but if you do need to replace the cat be sure you do not have an underlying problem that is damaging the cat especially if the miles are low, good luck.

Vettehappy

Hi,

Thanks for the input, I have 89K miles on the car and no other codes or problems that I know of. What would suggest to look for in underlying problems?
Since I am having this problem I decided to do some PM I have four new HO2 sensors ordered and am pulling the TB and intake manifold (leaking) will clean TB and replace all vacuum hoses that I can, 12 years under the hood is taking its toll, also new PCV, EGR & Solenoid, and fuel filter.
Thanks

toptechx6

Some maintenance can't hurt but I prefer a less shotgun approach. If you do get lucky and fix it you will never know what did it.
I would try to address the problem first then do the maintenance. You could still need a cat after spending all that money, good luck.

Vettehappy

Thanks, I will start with the HO2 sensors and work from there. Any other suggestions would be appreciated.