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Discussion Starter #1
Hi everyone, I have a 97 Thunderbird LX with the 4.6L V8, the check engine light came on recently and found 2 codes: P0155 and P0161, oxygen sensor heater circuit codes for both sensors on bank 2. I checked the resistance on the sensors and measured about 26 ohms on each sensor. I was not sure if this reading was good or not, but decided to replace the sensors anyway even though I thought it is odd for both sensors to go bad at the same time. Right after installing the new sensors, I cleared the codes and the check engine light came back with the same two codes. I cleared the light two more times and the codes still persist.

So I went back to the sensor connectors with my multimeter and found that I have 12V on the heater power wire but I do not have a ground on the heater. Do those two sensors share the same ground? How should I proceed in testing? Do they get a ground from the PCM?

Your help would be greatly appreciated.
 

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Yes, they ground through the PCM. The engine harness carries the front O2s to the PCM via the bulkhead connector on the passenger side and the rear O2s go through the transmission harness under the dash.

I had a P0155 and P0135 at the same time, which ended up being a short in the harness behind the intake. But the difference here is that those both share the same harness. Your issue does not.
 

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I don't know if this will help or not, but I had The CEL come on more than one of my Thunderbirds. I ran a can of Sea Foam thru the engine via the power brake booster vacuum hose, disconnected the battery afterwards and let it sit for a few minutes then reconnected it. This simple procedure corrected my CEL issue.
 

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Discussion Starter #4 (Edited)
Does anyone know which pins to test on the PCM for bank 2 sensor 1 and bank 2 sensor 2? If I check resistance between the pcm and sensors, and I get continuity then that means the issue is inside the pcm? Also just to make sure, bank 2 is on the driver side right? The sensors I replaced were on the driver side, just want to make sure I didnt make a silly mistake in testing the wrong side.
 

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I went through the same problem on my Cougar. Like you will find in the link Grog posted; it ended up being the EEC. Be careful because I went through two used ECCs that had the same issue as well. The Oxygen sensor heater circuits going out seems to be a more common problem that we all realize. I see a few posts on the Facebook page and here every once and a while with the problem.

My advice is get a good remanufactured EEC with a warranty.
 
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