I have a 1996 Ford Explorer Eddie Bauer Edition 5.0, the check engine light is on and my code reader gives P0161 and P0155 both stating that the O2 heater circuit sensor is bad. I replaced all 4 of the O2 sensors in the truck, cleared the codes but they still keep coming back. I have tried for a few days now to find something online similar to this but have had no luck. I am not sure what else to do. Please help!

 

Those diagnostic codes DO NOT state the O2 sensor heater circuit is bad, but instead point to the heater circuit. From the factory service manual: "Diagnostic Trouble Codes (DTCs) P0135, P0141, P0155 and P0161 indicate a short to ground, open, or short to VPWR in the HO2S heater circuit." There's more to diagnosing these codes than just replacing the sensor as the sensor would only partially address the "open" portion of the possible causes.

The P0155 points to the circuit for sensor Bank 2 sensor 1 and P0161 is for the circuit of Bank 2 sensor 2. You might start by looking for something common to Bank 2.

The power for the heater circuit on both bank 2 sensors is sourced from Splice S142. Confirming if you have power to both sensors with the key in the Run position would be a good place to start. The ground for each of the Bank 2 sensors is through individual wires that remain individual all the way back to the PCM. It's possible they could both be bad, but I'd start by checking for things common. That being said, splice S142 is also common to the Bank 1 sensor heaters, but maybe only part of the splice was damaged.

If you want a PDF copy of the troubleshooting section of the service manual for these codes along with the schematic diagram for the O2 sensors, send me a Private Message with the vehicle information, information being requested, and an e-mail address for you that can accept PDF attachments.

-Rod