I have traced the wiring out. O2 sesors were connected correctly. If yoou connect the harness for the front O2 sensor to either sensor I get a readig on the scan tool. If you connect the wiring harness for the rear O2 sensor to eitherr sensor I get a 0 volt reading. I have traced the wires to the EC...

Have already disconnected battery for a couple hours. Battery went dead and was replaced. Yes it does have black smoke when operating on front sensor. If you connect front harness to rear sensor the black smoke goes away.

I am working on a 1998 Volvo S70 with a 2.4L nonturbo. I replaced the front oxygen sensor(customers request). The car was getting a po130 code and black smoke out the tail pipe. After replacing the front sensor and turning off the check engine light, the car ran ok. Soon afterwards engine light came...