It was connected with old O2 sensor connector with heat shrink crimp connector. The CEL lights did not return. Engine is running normal again.
before the repair, the engine was running at high rpm, around 1200 to 1500 rpm when engine started. It did not go down at all even after engine was warm.
replace the o2 sensor with this product. wired it with heat shrink crimp connector to old sensor's connector.
the CEL warning light went away, but engine was still running at high rpm. It took about hour to two hours engine running to bring down the rpm to normal range.
now engine starts normal with normal rpm.
I drove about 10 miles and no more CEL lights.