I`ve 96 gmc with a 305 and the ses light came on the scaner said it was o2 senser on the right side but thanks to gm. their 3 on the right side is there any way to test them ?

What was the code?

There are actually 2 on each side, but the catalyst for the bank 1 side is routed over to the bank 2 side before it heads into the muffler.

Just keep in mind there are a total of 4 HO2S on this vehicle (unless it happens to be one of the few v-8s with 3), one bank 1 pre-catalyst, one bank 1 post-catalyst, one bank 2 pre-catalyst and one bank 2 post-catalyst.

Very often you'll get an HO2S heater code. If this is the case, I'd get a schematic and find out if there is a good power supply and ground to each of the 4 HO2S. If there is and they're all original, I strongly advise you to replace all of them. The heaters degrade with age, and the first one to set a code is usually just the first, if you know what I mean.

Remember to use plenty of penetrating oil, and it wouldn't hurt to pressure wash the sensors before you replace them.

Please post back and let me know how it goes.

I never got any numbers just went to autozone they put it on their scan tool. they said it was on the right bank. the truck has 72.000 on it undone the battery cable and the light has`nt came back on <img src="/forums/images/graemlins/confused.gif" alt="" />