rtonder wrote: "there shouldn't be any bare wires in the harness. The right front should have red/black, brown/pink, white/orange, and blue. The brown/pink is 12v right from the fuse box and supplies power to the heater only. If it was shorted at some point it may have melted the insulation away over time using several fuses. The white/orange is grounded by the ECU to turn on the heater. The remaining two handle the signal generated by the sensor. There would be no output unless the engine is running, the exhaust of which reacts with the sensor to create the output voltage. That said, the 12v power has no effect on the signal, other than warming up the sensor after start-up."
"Just so I understand, you have 12v at the orange female connector that is clipped to the bracket on the bell housing, right? That is a brown and pink wire in the harness that goes up to the engine and ties into the main harness by the coil pack. If so there are no other fuses affecting the O2 sensor operation other than the main ECU protection. I think I see red and blue in the photo, so guessing the "switch" wire for the heater is burned. That would keep the heater on all the time if it is grounded. If not, and the short has burned away, the sensor will not heat, you will not get a reading when cold, it will go to open loop and post the code. It may be the two signal wires were damaged at the point of shorting."
"The wires go up to the big loom on the cowl, then over to the corner of the engine compartment, then down through the firewall and into the ECU. The total run less than six feet. The 12v wire breaks away before the firewall and gets to the fuse box through the big connector that is hooked to the cruise control bracket."
"You can check continuity by pulling the ECU connector, the pins are in RAVE under the electrical library. Specifications are in the workbook under emission controls, exhaust."
"OK update, I see the white black, so you have five wires in the loom?"
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Rtonder is exactly right, in all respects; pay attention to what he is writing. The oxy. sensor built in heater unit function only when cold, so the rest of sensor will function correctly while cold; throwing up normal small fluctuating voltages from heat as exhaust flows around end of sensor. Once heated from engine and exhaust, built in oxy sensor heater shuts off; no longer needed during engine running hot. So, the built in oxy sensor heater gets 12 volts from brn/pink wire, which is grounded by ECU from oxy sensor white/orange wire. Once heated up, the built in sensor heater shuts off, ECU ground becomes shut off regulator in doing so. Now that it is heated up, red/black wire and blue wire receive small fluctuating voltages from oxy sensor, normal operation. On my 2004 Rover, I found that a small oil leak on rear of valve cover gasket, leaking down onto the wires of oxy. sensor, allowed for periodic short, so oxy sensor gave periodic voltage variations. I bought a good spray oil cleaner that had no affect on electrical hookups or on oxy. sensors (advertised as such on spray can), instant evaporation too, and sprayed the wires/looms all down, fixed the valve cover leak, and problem was solved. So contamination of wires, or hookup plugs, oxy. sensors, is critical; they must be clean and dry. Now, Mine functions well with cheapo or with best Bosch oxy sensors.

 

I will definitely take care to do as instructed earlyrover, I'm still a bit perplexed at that "wire" wrapped with the red/black and blue wires. I've dealt with the V/C leaks once before and have the whole top end off performing headgasket replacement. So now is the time for this kind of stuff as the harness is easier to get at.

 

Little update for those reading.. took apart the front 02 harness plugs, no oil contamination. I did OHM the red/black and blue wires, including the white/orange power wires. I have good continuity. I'll replace the front 02s just because I have them. I'll go from there.

Somebody either mentioned in this thread, or I read it in another, about having the ECM reset. Any input on this?

Basic plan is to get the thing running again and continue to diagnose it.