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CEL from rear O2 sensor on a 2006 Forester X


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I attempted the $5 mechanical fix, and apparently broke the O2 sensor (the housing got twisted and bent). Now, both the sensor and heater lines ohm out to infinity. Prior to my ham-fisted efforts, the computer was throwing the code for reduced catalytic converter efficiency. Now it's issuing a P0037 (heater control circuit low bank 1 sensor 2), which is understandable. Also understandable, and very annoying, is the fact that this code is issued again immediately upon a second start-up, after clearing the codes with a battery disconnect and pump of the brakes. At least the catalytic code was delayed by a 100 miles or so.

 

To beat the P0037, I've tried bridging the heater supply lines (the black wires) with various resistances, starting with 4.7K. The code stopped issuing when I got down to 330 Ohms, and the voltage across that resistor in-circuit was pulsed (didn't haul out my O-scope to the car yet).

 

My reading concerning O2 sensor heaters indicate a cold resistance of 3 to 7 Ohms is typical, and that the resistance increases as heater temperature increases. I measured the resistance across the sensor and heater lines of a universal O2 sensor at the auto parts store, and found 3.4 Ohms for the heater, and an immeasurably high resistance across the sensor lines. The later surprised me, but I suppose an unheated sensor could present such a high resistance.

 

My question is this: What resistances are optimal to bypass the O2 sensor? Can I fool the ECU with constant resistances across both the heater and sensor lines?

 

If not, does anyone here with a Tactrix OpenPort live in my neck of the woods (Dayton, Ohio)? If I understand correctly, one may selectively "mute" selected codes with an OpenPort and EcuFlash, preventing them from causing a CEL fault, and forcing limp-home mode.

 

Any and all advice is appreciated and welcome!

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You said it threw a code for reduced cat. conv. efficiency..P0420? I would be taking the car back to the dealer for a warranty repair for that one...Those cats are warrantied for something like 8 yrs/80k miles, Or if your vehicle is an 06' It might still be under the manufacturers warranty of 3 yrs/ 36k miles....This is what I would be checking into first....

I do have a Tactrix cable for my WRX which is obviously tuned by Romraider OS..I'm all the way over by Philadelphia PA though..:lol:

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