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I have an intermittent P0138 that has been popping up the last two weeks. I've cleared the CEL and watched the voltage but it continues to trip due to occasional high voltage. I just ordered a new sensor from eBay to replace it. I realize I am rolling the dice on not buying the Denso 234-4364 to replace the failing OE but there was a $130 difference... Has anyone used one other than the Denso? Rockauto had a cheap one but it wasn't valid for shipping to CA.
It looks like a pretty straightforward replacement. Any tips for replacing?
Start soaking with PB Blaster or equivalent today. You will be happier when it is time to replace it :P Those can get hard to remove. Mine actually came out pretty easy when I changed CAT's but I did soak it the day before just to be sure.
Did you check all wiring and are you sure the CAT is indeed operating correctly before deciding it was the sensor?
I haven't gotten under the car yet but I have not noticed any rattles that would indicate issues with the CAT. Any suggestions on how to check otherwise?
I was able to remove the secondary sensor with just a regular 22mm combination wrench...soaked the sensor in penetrating oil overnight, and hit the end of the wrench with a mallet.
In the meantime... I got a P0420 this morning. Does this confirm the TWC is bad or just a symptom of the bad O2 sensor?
A temperature test is one method (testing temps on both sides of the cat. You can find instructions around for that.
A pressure test can also be performed, but requires more tools, drilling a hole before the cat (you just screw a plug in after), etc.
A bad cat will not necessarily rattle. As a matter of fact, the two I have dealt with you could not tell outside the tests above. If they are bad you will notice a lack of power, but if it happens slowly over time you actually can become accustomed to it and not even notice that until you fix it and notice the power came back all at once.
In the meantime... I got a P0420 this morning. Does this confirm the TWC is bad or just a symptom of the bad O2 sensor?
0138 just means that the voltage on sensor 2 (the one monitoring CAT effectiveness) is not lower than 1.2V or lower than sensor 1 voltage (read by the ECU as too much oxygen in the exhaust stream). So that can either be due to wiring, bad sensor, exhaust leak or bad cat.
0420 means the cat is operating below threshold. Again, could be wiring, bad sensor or a bad cat. But the 0420 is much more likely to be the cat and not the sensor.
Happy to report a completed o2 sensor replacement and catalytic converter. I picked up an OEM TWC off eBay with 14k miles on it. Over the course of the last few weeks, the catalytic converter developed a loud "bucket of bolts” rattle. This all but confirmed I’d be replacing it.
Upon finally getting all 5 bolts off (thanks for the PBlaster suggestion) I replaced all hardware and gaskets with new ones. Liberal anti-seize was applied. It was a 1 to 1.5 hour job including the o2 sensor. The TWC was crumbling and moving around inside. The cheap o2 sensor from eBay that I bought plugged directly in and is working perfectly. The old o2 was clearly abused by the catalytic converter. Thanks!
I went through this very thing this summer. Eventually the O2 code came back because of the aftermarket cat I used. Ended up using the defouler trick to make it go away.
Oxygen Sensor Bank 1 sensor 2 - P0138
