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P0138 code

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    I am having an issue with the p0138 not clearing Problem originally started with a P420 code. Replaced the upper O2 sensor and that code cleared and never came back. But right after that, I got the P0138 that won't clear. Replaced the lower O2 sensor (that i replaced 6 months earlier) and that did not clear it Monitors also not completing are evap (most the time) O2 (some of the time) and HTR O2 (some of the time). Not sure if it is all the samer issue or a couple issues. Any thoughts? Someone said something about something that heats the O2 at start up so it gets to temp quick. Is there a module for that I can check? A fuse? I have been googling for a few weeks and can't come up with anything. Thanks in advance.
    • Edited 1 times, last by MR_LUV on .
    Thanks. That is one of the things I found in my google search. Was hoping someone who has had this issue could advise what worked for them.

    To add more info, other than the check engine light I am having no other symptoms. No foul odors, no driveability issues, no misfires..... just the p0138 code (and sometimes the incomplete monitors). I checked and cleaned connectors with electrical cleaner last night and did not see any issue there. Let the car idle on the driveway for 30 minutes and no codes. Code came back after 10 min of driving this morning. Hoping to avoid a diagnosis charge at the dealership
    backroad101 wrote:
    I am having an issue with the p0138 not clearing Problem originally started with a P420 code. Replaced the upper O2 sensor and that code cleared and never came back. But right after that, I got the P0138 that won't clear. Replaced the lower O2 sensor (that i replaced 6 months earlier) and that did not clear it Monitors also not completing are evap (most the time) O2 (some of the time) and HTR O2 (some of the time). Not sure if it is all the samer issue or a couple issues. Any thoughts? Someone said something about something that heats the O2 at start up so it gets to temp quick. Is there a module for that I can check? A fuse? I have been googling for a few weeks and can't come up with anything. Thanks in advance.


    ok.. couple of things.. as MRLUV posted, did you check to see if you have any exhaust leaks, intake leaks?

    and look at what MRLUV posted.. see that curve of voltages around stochiometric? which is the optimum air/fuel ratio, that voltage ranges from 0.1v to 0.9v. Using your obd2 scanner, look at the live data of the 2nd o2 sensor, is it within those values?

    If you have an obd2 scanner that can look at mode6 data, check the 2nd o2 sensor's data. Is it within the values or at the limits?

    And.. you're not going to want to hear this.. just because you put a "new" o2 sensor in doesn't mean it wasn't defective! I had that on my project civic car. Had a brand new ntk brand sensor, was faulty! You can also check the o2 sensor via a multimeter, in my case, the resistance was infinity! Which means the heater of the o2 was bad.

    I believe that the tC uses denso or ntk brand's of o2 sensors. If by any chance you used bosch, then I'd say there's your problem. They are notorious of not working with japanese vehicles.

    check all those things, there is NO need for you to waste your $$$ at a dealership when you can do all these checks yourself. you've already done most of the work, just need to know what/where to look.. keep us posted.
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