I replaced the upstream O2 sensor with a Bosch brand, the same brand used in the down stream I replaced last year. Took the car out for the drive cycle, and came back home check engine light went off and put on My OBD-II reader and all systems are a go.
So it was the bad upstream O2 sensor putting out the PO420 Code. Just got back from emissions station passed with flying colors.
Thanks! for everyone for there input on this.

 

Hi in New to this and I have a 87 305. V8 4 barrel carb h.o with 93,500 on it stock, I just got a tune up wire plugs gas filter pvc cap ext, ever since then when I get on the high way around 65 my check engine light comes on and I'll pull over and let it idle for about 3 mins and lights goes off, I can drive around town and no light only when I hit that 65 ..please help ibalrwady changed the wires again ,, thanks

 

Viarella87SS
Have you had the car put on a code scanner to see if your putting out any codes?
If you have not go to Autozone or O'Rileys and they will check it on there scanner for no charge.

 

what auto parts store will read an ABS code for free? if any??

 

free scans are only for check engine codes. not abs or transmission. those need the more intense scanners that only mechanics and dealerships have.

 

Not entirely true. The scanners the advance auto parts locations have can read abs codes. I bet if claydoh called their local advance they could read it

 

Really??? they always told me they couldnt......they said if the check engine light isnt on they couldnt pick up any codes. i know they sell the scanners that are able to read it all. but they wouldnt use them for me when my abs light was on. had to go to my mechanic