Code P0139 of Honda CR-V 2005

My CR-V 2005 ( 190,000 miles) got a CEL on ( Nov, 2014)( Colorado). Dealer’s scan showed code: P0139 : O2 sensor 2( down stream) slow response( Dec,11,14). I took my car to a shop close to my house for replacement of O2 sensor. After replacement, the mechanist told me, my sensor( new) " still stuck full rich". he suggest if my CEL is on with same code ( P 0139), I’ll need to change the Catalytic Converter ( Jan, 8, 2015). So far my CEL has been on & off 3times ( by itself) with the same code P0139. 1st time was 2 days after the replacement, just almost a minute before the empty -gas-tank light was on, and off 3 days later. Ten days after that, CEL was on, just before I filled up my empty gas tank, and off 2 day later.The 3rd time was 3 days after the 2nd, my gas tank is half empty. I decide to fill up the tank and started my car , CEL was off right away.:-). I talk to my mechanist( Jan,28,15), he said My Converter is borderline ,still needs to be replaced :-(.My car has been running OK before, during & after the CEL on & off. Do you have any advices??
Thank you very much

Have the fuel pressure check when the tank is low
Possible causes

  • Faulty Rear Heated Oxygen Sensor Bank 1
  • Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
  • Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
  • Inappropriate fuel pressure
  • Faulty fuel injectors
  • Intake air leaks may be faulty
  • Exhaust gas leak

if your catalytic converter was that bad, you’d have P0420 catalyst low efficiency code. The downstream sensor would be fluctuating at the same rate, or nearly, as the upstream sensor

I’m very skeptical of the cat diagnosis. I think the mechanic is headed down the wrong path

One more thing . . . what brand sensor did the mechanic install?

The engine computer monitors the O2 sensor before the cat and the one after the cat and compares the readings. They should vary w/time in a certain way w/respect to each other. It sounds like the one after the cat isn’t doing what the computer thinks it should be doing. A full rich reading could indeed mean the cat is caput. But it could also mean the O2 sensor before the cat is caput, or that both sensors are good, but the engine is running very rich (too much gas) for some other reason. A cat can only do so much. If the input to the cat contains a lot of raw gasoline, the cat won’t be able to catalyze all of it, and a rich post cat O2 sensor reading would result.

Good comments above about things to try. The factory service manual for your car probably has a recommended step by step procedure on what the mechanic should do in this situation. Ask your mechanic to show you that procedure and tell you what the result of each step has been to date.

Hi knfenimore, db4690, GeorgeSanJose,
Thank u all for giving me the ideas. I’ll check the tank pressure & Upstream O2 sensor.
My New O2 Sensor ( downstream) is made by NTK ( japan) .
This morning, with gas tank is just half, my CEL is still off, I fill the tank up. Guess what: CEL is ON!!! I check the tank Cap:, seem like O.K. I don’t know how to check the pressure but I can learn.
My mechanic just said " my car needs new converter because it’s borderline".
Will contact u all, if something new coming up.
Thank you very much.

@tracdaubac If you filled up and the check engine light is on, it’s almost certainly not because of the catalytic converter

Best get the codes read again . . . might have a different code by now

Your mechanic is giving you just plain bad advice, in my opinion

If he knew how to check mode 6 data, he’d know if the cat was truly “borderline”

But I somehow suspect he’s not checked that yet, or doesn’t know how

I wonder if he’s even checked for a pending P0420 code

I wonder if he’s performed a backpressure test, or even up a vacuum gauge

I might be wrong about this guy, but I really think he’s grasping at straws as far as the catalytic converter is concerned

I know you’re just relaying information, but so far we haven’t heard one good reason why the catalytic converter should be replaced