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recommendend diagnostic steps for p0302 and p0137

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Fivel, Jul 11, 2021.

  1. Fivel

    Fivel Junior Member

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    Hey Folks
    Just got some trouble codes today, looking for advice on troubleshooting.

    Got the above codes, car shuddering, some difficulty with acceleration. Weirdly, the check engine light was flashing, and would turn off after flashing for a bit. The shuddering would also go away. Later checked and also go p0301 and p0304. This happened out of the blue, haven't had any other issues.

    Car is a 2007, has just over 100,000 miles on it (I've only had it for a year though).

    I looked through several other threads (including this one, this one, and this one) and I have a few takeaways but would appreciate any suggestions or if I'm misunderstanding something.

    • The p0300-304 sensors are indicating misfires; my first step is going to be to replace the spark plugs. AFAIK, they haven't been replaced, so at 100,000miles this couldn't hurt, and it's inexpensive and relatively easy to do.
    • I know this may not be the source of the problem though. Is there something I should pay attention to/look at when I change out the spark plugs that might tell me more info? Other threads indicate it could likely be the fuel injector — is there a way to test, or should I just replace the plugs and then see what happens?
    • Regarding the Oxygen Sensor (bank1sensor2), is it possible that code went off *because* of the misfire? EDIT: I looked at the OBD while driving, and the sensor was moving between 0.2 and 0.9 volts, and was mostly ~0.7, which is seems normal/okay? (this was just local neighborhood driving though, not highway, which I gather is how you are supposed to check) If the O2 sensor is definitely unrelated (i.e., coincidence that they both went off now), should I just go ahead and replace it? Or start with addressing the misfire and go from there?
    Thanks for any tips/suggestions.
     
    #1 Fivel, Jul 11, 2021
    Last edited: Jul 11, 2021
  2. JC91006

    JC91006 Senior Member

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    It just seems strange you have 2 misfire codes come on at once, different cylinders. I would suspect it's not your plugs, failing at the exact same time.

    But since you are at 100k miles on a 14 year old car, I would just go and replace the plugs. Before taking them out, you should swap the coils around, see if the misfire jumps to a different cylinder.

    I would think this is more of a fuel delivery issue. Fuel injectors, fuel pump type of problem. But you should replace the plugs first, that's easy enough to do. Clean the throttle body and MAF sensor while you're in there
     
    #2 JC91006, Jul 11, 2021
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  3. ChapmanF

    ChapmanF Senior Member

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    There was a pretty good article on misfire diagnosis in the Second Quarter 2009 issue of Toyota Tech (starting on page 15).

    My only misgiving on mentioning it here is that it was specifically on how some of the ECU features for supporting the diagnosis changed for Gen 3, so it probably doesn't map seamlessly onto your Gen 2. But it's still a good source of general ideas and ways to look for information that can help.
     
    #3 ChapmanF, Jul 11, 2021
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  4. Fivel

    Fivel Junior Member

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    Thanks, that article was very informative indeed! I guess it doesn't map exactly onto the Gen II, but it is super helpful to understand what was going on with the misfire — and does seem to suggest that the O2 sensor code *was* caused by the misfire, given that misfire I had was a "catalyst over temperature," which the article informs is indicated by the MIL blinking (still not sure why it turned off rather than staying on, but I guess have to look more into how Gen II monitoring worked for an explanation).

    Hopefully will get to changing the spark plugs tomorrow, and then do a little driving with the OBD plugged in — it's not techstream, but I'll see what I can learn, based on what that article points out the computer will log. Hmmm.
     
    #4 Fivel, Jul 11, 2021
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    Depending on : the severity of the misfire, the emissions regulations for a particular year, HOW the OE interpreted and implemented those regs, (and solar activity vs lunar cycle) ; the engine ecu can do one of four actions. It can, 1) do nothing (but keep track of the misfire data) 2) set a pending code, then turn on the MIL if it happens again next drive cycle 3) set a hard code and turn on the MIL immediately or 4) flash the MIL if the misfire could damage the catalyst- and it can do most any of these actions in combinations. So in your case it flashed the MIL then set a pending code? Some cars can also disable the fuel injector for the misfiring cylinder- some might do so for a short time then turn it back on, some might leave it off until you cycle the ignition.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Jul 12, 2021
  6. Fivel

    Fivel Junior Member

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    So just to update/close this ticket (so to speak):
    I replaced the spark plugs last week. They were showing their age, and it definitely were ready to be placed, but I also didn't see any real problem (carbonization etc) with them that would have caused a misfire — I think anyway, not an expert on this, attached photos of the removed plugs, if more experienced folks notice something wrong with them would love to hear for future knowledge.

    Haven't had any problems since, but I think it was mostly a random occurrence (i.e., not specifically caused by the plugs, or other part). The other bits of information that might be relevant/for curiosity's sake: 1) the gas tank was nearly empty when the misfires occurred. Not single light blinking low, but on the last indicator light. I know low gas isn't going to cause a misfire, but I wonder if any impurities/water in the tank would have been more likely to cause a problem with the tank low? Just wondering. 2) I also put in a bottle of Techron Fuel Injector cleaner in the tank, and after that plus the spark plug change, I'm now getting ~52mpg, when I was getting ~46mpg before. Now I'm just a tad bit annoyed I didn't do them separately, so I don't know which change led to the mpg increase. Perhaps it was an issue of the injectors, and the cleaner removed the issue? So yeah, don't know what caused the misfires that day, but after this minor maintenance, the car is running better than it was before, so I can't complain.

    Thanks all for the suggestions!
     

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    #6 Fivel, Jul 20, 2021
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    The plug on the right looks to have a noticeably larger gap (the "pad" is gone from the ground electrode?). All it takes is enough increase in kilovolt demand to exceed the coil's ability to produce under load.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Jul 20, 2021
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