ccnova

I bought a 97 GMC 1/2 ton 2 wheel drive 5.7 Suburban with 170,000 miles and intake gasket problems about 2 years ago and with the help of this forum fixed the intake problems and replaced the fuel injection spider also. It runs great ever since but in 10,000 miles since has had code P0430 about three times and only if it is driven in stop and go traffic for more than a few days. I mainly use it on the road and have no problems but if used "in town" for a week or so it will throw this code. I borrowed a code scanner and it told me that;
O2S B1, S2 STF X (No value)
And
O2S B2, S2 STF X (No value)

Can anyone tell me what this means and if it means I need to replace an O2 sensor which one?
Thanks for any help.
ccnova

J-Ri

Well, that "no value" is what might tell us something, if there were a value there. You might want to find a scan tool that is more capable and see if it gives you anything. If it's got the original O2 sensors, replace all 4, they usually last about 100k miles before they start reading off. See if that fixes it, if not, it's probably a problem with the cat.

Although the code if for bank 2 (could be either sensor, need to check the voltage on an oscilloscope to see which one), if they're all the same age, just replace them all.

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ccnova

the scanner I am using does actually give values for the sensors but for this one it just gives an X which I assumed meant no value. I will probably check tomorrow when my son gets home with it. Is it possible its defective and giving no reading?
Thanks,
ccnova

j cAT

as recomended if these o2 sensors are very old over 100,ooomi or operated with the intake manifold leak occuring they should be replaced....

on the cat failure ,,,I would swap out the down stream O2 sensors...then see if you now get the dtc o420 code if so its the o2 sensor....If the code repeats dtc0430 then is the cat that is defective..

WHENEVER THE CAT'S ARE REPLACED REPLACE THE O2 SENSORS UPSTREAM, OR MAKE SURE THEY ARE GOOD....

a bad O2 sensor will destroy a cat quicky ...

ccnova

Thanks for the help everyone! I will follow your advice and replace the downstream sensors first. Having two kids in college kinda cuts my funding alot! If the code comes back well then thats another day down the road a little and I take one day at a time! Its all I can afford !!! Again thanks for the help.
ccnova

j cAT

don't buy new O2 sensors YET...first swap the down stream sensors to see if the dtc changes to the po420 from the po430 dtc you have now....then you will know its only the O2 sensor that is bad not the converter..

the upstream sensors if bad will damage the cat so if these sensors have over 100,ooomi replace them..the downstream sensors are only monitoring the cat for any loss of effectiveness..in reducing pollution...

fp1529

I am not a mechanic but my 99 Suburban had an 0430 light on forever. I tried everything in the book and the only thing that worked is a new CAT on the passenger side. It was a little over 200.00 at a muffler shop. If you know how to weld I would cut the old one off and put an aftermarket one on. Mine is an aftermarket and no engine light after 1,000 miles. Good luck!