About a month ago I replaced my catalytic converter, a few weeks later the O2 sensor went out. I replaced that too and I'm still getting a check engine light code for the same sensor. What else should I do? The guy at autozone said to make sure that the O2 sensor is getting power and that it's plugged in and it looks like it's getting power and it's plugged in.

Update- last two oil changes they've also said that my oil levels are dangerously low.. even though I've been changing the oil on time. Not sure if that's relevant or not.

  • You had the codes read again and cleared? – Pᴀᴜʟsᴛᴇʀ2 Aug 3 '16 at 21:42
  • Yes I have! Same code – Katherine Aug 3 '16 at 21:43
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    What is the make/model/year/engine of the car? What exactly is the code you are getting? – Pᴀᴜʟsᴛᴇʀ2 Aug 3 '16 at 21:45
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    To break in a cat, basically, run it at idle for 5 minutes on first startup, then bring it up to 2500 for another 2 minutes, shut the vehicle off and let it cool completely. This gives the honeycomb a chance to expand as it's supposed to. If not done correctly, the cat can self destruct in a month or so. – Pᴀᴜʟsᴛᴇʀ2 Aug 3 '16 at 23:18
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    What engine do you have? On the Impala there shouldn't be a p0136 code. p0135 is for the b1s1 heater. A low voltage code on b1s2 would be a p0137 and a heater code for b1s2 would be p0141. – Ben Aug 3 '16 at 23:32

Check the O2 sensor connector for pin fit and corrosion. You will have (I assume) ignition voltage (it may be 5v) on one heater wire and a pulse width modulated ground on the other heater wire.

If you don't have power and the Emissions 1 fuse isn't blown, voltage drop test the wire to find the break. If the fuse was blown I'd expect more codes than just the p0036 code.

If you do have power, check the ground wire. You would want to do this with a digital storage oscilloscope to check the waveform for drop outs. I think you can do this with a digital volt ohm meter as well since it's PWM you would see half the voltage you see on the power wire. Or if you had a known good spec you could try to get a hertz reading on the PWM wire.

If the wiring checks out try replacing the O2 sensor again before replacing the pcm.


Depending on the maker of the cat it’s also possible to have a defective new aftermakrket cat if it’s not an oe supply

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