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I just made my account hoping I could get some help. I just recently bought a 2004 Honda civic ex 5 speed and the check engine light was on I put my scanner on it and it was throwing a po135 so I changed the first o2 sensor with a denso air fuel ratio sensor because any other ones I put in there wouldn't work. Also I put a brand new catalytic converter and exhaust on it and I cleared the code and the check engine light went out for like 50 miles then came back on and now its throwing a p0138 code saying the voltage is too high but my second o2 sensor was good before why is it throwing this code now?

 
Rep Power: 519

Sounds like it might need the rear O2 sensor now.

 
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It was not malfunctioning before I don't understand why it would need one now

 
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I have been trying to fix this problem now for a couple weeks I'm trying to get it inspected and I cant get the light to go out. I put a new catalytic converter and exhaust on it also the oe denso air fuel ratio sensor because that is the only one that I got to work the light went out for 50 or 60 miles after putting that in and now the code is a p0138

 
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I have been reading that replacing the second o2 sensor will not fix the problem and I cannot find an answer for what to do

 
Rep Power: 146

Sounds like we are not getting the whole story here:



Why exactly did you do this extremely expensive repair? Did you have a cat code before you did this? There is really no reason to do this unless you have a code related to the cat.



Because things break?


P0138 - O2 Sensor Circuit High Voltage Bank 1 Sensor 2


Are you sure you didn't short anything when replacing the cat? No water or dirt in the O2 sensor connector?


Could be an ECU problem, but the sensor is literally $40 on Amazon, get the Denso one, as you have seemed to learn the hard way unfortunately with your Air/Fuel sensor.


Tell us more about what you did to the car and more importantly, why you did it.



What? Who told you that? Unless you know what the problem is, you don't know it ISN'T the sensor....and the sensor is relatively cheap....

 
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Alright so I bought this car right after Christmas and the previous owner said the reason the cel is on is because the upstream o2 sensor is bad and he said he took it to a mechanic and had it diagnosed. I have a scanner so when I got it home the code was p0135 o2s ckt no activity detected 1/1 so I replaced it with an after market I found on ebay for like 20 bucks then after I did that my light would go out for a minute and come back on and then the code was p0134 no activity so I looked into it more and found out my catalytic converter was bad so I replaced that and the rest of my exhaust but it still would not go out then I read some more and found out that most of the aftermarket o2 sensors do not work because of a narrow band so I ordered an oe denso air fuel ratio sensor and put that in and that seemed to work for me for like 50-60 miles then my light came back on and I scanned it and now its throwing a p0138 code

 
Rep Power: 519

You touched it ---- and now it's got a code for it.
If a mechanic had done the work and then it popped this code shortly afterward, you would be blaming him. Right? Right?


You ought to replace the specified sensor (use the correct brand) and see if it fixes the problem.

 
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yeah I touched it but why would my car drive fine for 60 miles with no light then come up with the code p0138 pending? I don't take my cars to mechanics

 
Rep Power: 519

It was good for 60 miles. Then it went bad.
**** happens.
Replace the sensor.
If it solves the problem, you're done.


Maybe your new cat is garbage, the guts aren't secured, they are moving around inside the can, the tip of the sensor has been broken off.
I've seen this more than once, but not on a brand new cat.

 
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why does it say pending after the code? it says p0138 high volts mod 1 of 2 and then you click the down arrow on the scanner and it says pending. I don't understand that

 
Rep Power: 519

The code set criteria would tell you that particular code is a two-trip type....meaning it has to fail two self tests in a row before it sets the code and turns on the CEL.


After the first fail it's flagged as a temporary or pending code.
If it fails the second test on the next trip or drive cycle, it gets moved from pending to permanent and turns on the CEL.

 
Rep Power: 519

I also have no idea what features your scanner has, nor what it is capable of.

 
Rep Power: 146

Yea, that $20 sensor will not work for the Air/Fuel sensor (bank 1).... ahh, you figured this out by reading, good....




Still not sure how you determined your cat was bad though? Did you have a code for this or just guessing?



Well, the A/F sensor probably IS working still, just now your O2 (Bank 2) sensor is shot.


This one is a cheap sensor! This one is the $40 Denso one that you need. Go to the Denso website and select your car to get the correct product number and get it off Amazon, or wherever you like.


Ezone, if the primary A/F sensor is malfunctioning, is it possible that the secondary O2 sensor may not throw a code, even if it is malfunctioning? Or can you have both malfunctioning and have them both throw codes at the same time?

 
Rep Power: 519

This would be accurate. There are many cases where a set code can preclude testing for another code or fault.
Quite often it's impossible to tell if there are other faults until the PCM has completed all of its self tests during OBD2 drive cycles.


An active AF sensor code will prevent the computer from running certain self tests for the rear O2 sensor.
The computer will not run self tests for P0420 (cat code) if there are any codes related to O2 sensors.