my engine light came on--replaced o2 sensor now it's on again for open circuit on rocker arm?

Question

Our engine light on 98 chevy s10 4 cyl. came on and said o2 sensor behind catalytic convertor.Turned it off and it came back on and read the same. We replaced it. 24 hours later it came on again. Auto zone read it as rocker arm with open circuit. Advance read it as the same o2 sensor we had just replaced. We recently had the rear seal and clutch replaced before all of this happened. The truck has 135,000 miles on it.

Answer 1

When the code reads for the O2 sensor, it means that there is either somehting wrong with the O2 sensor's circuit or that it is seeing a reading that is out of tolerance. The O2 sensor could be bad but that is not necessarily the case as you have discovered. You need to have a full diagnostic run by a qualified emissions tech to determine the cause.

Since it's the downstream O2 sensor, I'd bet that your cat is worn out and needs replacing. The mileage on your truck supports that conclusion. However, you should go with a full diagnostic run as I said above. Reading the code tells the technician where to start looking; it does NOT tell you what part to replace!

The "rocker arm" reading doesn't make any sense.

Answer 2

the rocker arm repair is a joke, you would have a misfire code. the rear 02 sensor measures how much 02 is coming through the cat and if it sees to much oxygen it will turn the light on and usually it is the cat/efficiency is to low. very rare the 02 sensor is bad, but proper diagnostics will determine if the cat. is weak or not.