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Discussion Starter · #1 ·
This is just a follow up thread since it seems I actually was able to fix my wife's 05 2.4 LX sedan. The P0141, "Sensor 2 Heater Circuit Malfunction" has been the one and only code to pop up so far on her car over its 112,000 mile life. I read all I could find web wide, and here, about the experiences others have had attempting to reconcile this, and I guess I got lucky, but I found a Bosch OE style replacement and installed it a couple of weekends ago, cleared the code, and she hasn't reported any sign of the light coming back on past its initial check yet. :thmsup: " 'Tis better to be lucky than good!"

In testing the original sensor's heater circuit I found it was setting a hard fault with a reading of 217 ohms. I really had expected to see a completely open circuit, so I learned something. Now, the new Bosch sensor's heater circuit reads down to 3.5 ohms, which had me a little concerned since there were a few reports out there stating the resistance was perhaps too low which would allow high enough current flow to somehow damage the ECU. I spent a lot of time researching this before using the Bosch sensor.

I found that the Oxygen Sensor Heater circuit is most likely (the best I could follow) powered up by the A/F Relay, so all the ECU does is control the operation of the relay, like flipping a switch, which means the heater circuit resistance has no relevance at all in relation to current draw through the ECU itself. So, I decided I'd give it a shot and go ahead with the Bosch installation ...and, so far no problems at all.

Oh, and something else we both also noticed, although I can't confirm for sure. Once I installed the new sensor and reset the ECU the car actually ran quieter, at idle, and has averaged slightly better fuel mileage. I'm only guessing it was in "fail safe" mode or maybe staying in "open loop", and the ECU had changed its priorities, or was just averaging fuel and ignition maps as long as the MIL was lit. Not that important, but an interesting symptom detail that I must have missed back in Fuel Injection class.

The wife says it's running like new again! :D

-Roger
 

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Discussion Starter · #4 ·
And, as my luck would have it... almost the same day I post this up the check engine light comes back on. I ran the scan tool, and guess what? P0139 ...so I'm going to hunt a Denso on line, as well as contact the seller of the Bosch sensor to see if he will refund my money as the part is defective.

So, lesson learned... hopefully this thread will help someone else here to not make the same poor decision about buying the cheaper part. That's just the way it goes sometimes.

-R
 
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