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Hi, I'm new to this forum but not new to Civics. My problem: P0139 Slow downstream oxygen sensor. 2005 Civic LX Special Edition Standard transmisson. 160,000 miles. Computer 378230 PLM A14. I have a new downstream Honda Oxygen sensor. $400. Rebuilt Computer same #. $600. Checked all wires for continuity from Oxy Sensors to computer. All good. Checked all 4 grounds from computer to chassis. All good. Both oxy sensors register on my scanner. Scans are both are good. Power to Oxy Sen heater is good. I can not get the computer to ground the oxy sen heater. I connect a test probe to heater circuit , power to probe to ground and test probe will not light during key on or during engine running. I refuse to spend any more big $ to take it to Honda. PS, The civic runs great and I currently have black tape over the engine light. Can anyone help me fix this P0139? Thanks, Rick

 
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OK, no replies yet. Let me try another approach. The secondary oxy sensor heater ground is a black and white wire going into pin A 14 in my ECU. This grounds through, I believe, a transistor. It grounds when the ECU determines it needs heat. Where does this actually ground to? It must be a pin out from the ECU going to the chassis somewhere. Any ideas? Thanks,

 
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It would go to one of the ECMs grounds, there are quite a few.

Here's the entire troubleshooting for that fault, I know it isn't very helpful.

 
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Thanks. I have found 4 grounds that could be the ground I'm looking for but they all check out OK. I'm hoping some one knows a 5th ground. I've done that procedure at least 10 times.

 
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Honda issued a Software update for that specific code on certain cars. Search for honda tsb 07-019 for more details.
Go to your Honda dealership,

 
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Post #17 in this thread has a copy of TSB 07-019. https://www.civicforums.com/forums/3...placement.html

 
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Thanks for the info on the update. Yes, I know about that. Honda will charge me $200 to test my computer to see if it is OK, then update my computer and to link my key to the computer. If the computer is bad, I still get the charge and they can do the same thing to my $600 rebuilt computer. After spending over $1000 already, I really don't want to spend more and find out both computers are bad. If I could find a salvaged honda with the same computer as mine, I could replace the computer, keys, and ignition module. But then, the problem may not be the computer and I then spend more money.

 
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That's funny. You didn't read the bulletin?
Only do what the bulletin says to do.

The bulletin says to update software. That's it.
Not test it. Not replace it. Just update it.

Call your dealer. Call some other dealers. Ask the price to update software in your pcm..

 
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Thanks for the responses. If I thought the bulletin would fix my civic I would do it but I continue to know the problem, just not the fix. I wired an LED between Ox1 heater positive and negative. It blinks on/off quickly exactly as expected in order to heat the Ox1 to that certain temp. I then wired an LED between Ox2 (P0139 is Ox2) heater positive and negative. It didn't turn on or blink any indicating the heater circuit is bad. The positive wire does work. Just not the negative. The negative is turned on and off by a transistor. The transistor gets it's signal from something. It is grounded some where. Any help is appreciated before I just loosen the fuel injectors and drive it up a mountain until it burns up.

 
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My question from before: "The negative is turned on and off by a transistor. The transistor gets it's signal from something. It is grounded some where. Where?" I started getting a P0420, cat converter below threshold. I bought/installed a CARB compliant converter. It's been 6 days and I haven't gotten any codes. Today I went to a salvage yard and traced the computer wires into the engine compartment looking for an unknown ground. I only found the 4 ground wires bolted onto the water thermostat. Mine are all OK. So I think there is NO other missing ground to the ox sen heater circuit. Any thoughts? Rick

 
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ECU controls the heater on pin A14 by applying a ground. It would go to one of the ECM's internal grounds. The ECM main grounds are on four pins (A4, A5, A23, and A24), all of these ground to G101 (top of thermostat housing). There is still another ground from the battery to the engine.

The troubleshooting for that code mentions measuring the sensor output voltage with the engine warm and at 3k rpm. What was yours reading?

 
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Update, My car threw a new code. P0420 Cat converter below threshold. Comparing scans of OxSen1 and OxSen2 showed that the cat was not functioning. I replaced the cat with a CARB compliant. I cleared the codes. No codes since I replaced it. None. So, to my surprise, for the last 4 years everything was OK except the cat converter. The heater on OxSen2 still doesn't work but that doesn't throw a code. DONE.

 
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woah, so it was the cat?
thanks for the update, it might help someone else in the future