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Multiple Error Codes - P0138, U0293, U0100

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jake Miller, May 16, 2023.

  1. Jake Miller

    Jake Miller New Member

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    Hey all,
    I've perused the forums before but I finally signed up today for some feedback on a recent problem. I just got a check engine light the other day and was waiting for a good time to sit down and run the codes, but today I got full lights when I turned it on (red triangle and all).

    When I pulled codes, I got the following errors:
    P0138 07E8
    O2 Sensor Circuit
    High Voltage Bank 1
    Sensor 2

    U0293 07E8
    Lost communication with hybrid Ev power train control module

    U0100 07EA and 07EB
    Lost communication with ECM/PCM A

    Last time I got the red triangle, I got the P0138 code, and based off of some feedback, I cleaned the air sensors, and it seemed to work alright after that. I don't remember getting other codes at the time. This time seeing these other codes pop up, I'm a little more hesitant to try the same fix.

    So does anyone have some good starting points? I'm not a very knowledgeable person with electrical fixes yet, but willing to learn. I saw some other threads where people solved 0293 codes by checking/replacing fuses, but I don't know if that same issue could cause the 0138. Perhaps a battery problem? It does show that it has a roughly 2/3 charge on the energy monitor.

    Any help or another thread recommendation would be greatly appreciated. Thanks.
     
    #1 Jake Miller, May 16, 2023
  2. dolj

    dolj Senior Member

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    If you're really serious about becoming more proficient in diagnosing electrical/electronic issues, then you need to purchase a mid-tier multimeter (if you do not have one already) then you need to learn to use it by finding some good tutorials on YouTube that can teach you the basics of multimeter use and follow that up with some on basic automotive diagnostics.

    Search this forum for Prius Repair Manual or Prius Electrical Wiring Diagram to download as you will need that information to guide you in diagnosing any codes you might pull from any of your car's ECU.

    The P0138 indicates a problem with the electrical circuit of the upstream oxygen sensor. It is seeing voltage higher than it should be. The wiring damage may have in turn damaged the sensor or the sensor heater.

    The U0100 indicates a communication problem between the power control module and the engine control module.

    So, it seems likely you could have wiring damage in wiring that is common to both areas. Or, two unrelated wiring issues.
     
    #2 dolj, May 17, 2023
  3. Jake Miller

    Jake Miller New Member

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    Yeah, my neighbor/friend has a multimeter that I can surely borrow.

    I have had a feeling that this could be an electrical problem especially because I have an uncovered fuse box (have a new cover on order). Coincidentally, we had a ton of rain (torrential at times) right before this started popping up. It would be nice to rule it out, so does anyone know what fuses could effect all or some of these systems? Does it make more sense to check all of the fuses?
     
    #3 Jake Miller, May 17, 2023
  4. mr_guy_mann

    mr_guy_mann Senior Member

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    P0138 code description is Bank 1 sensor 2 (downstream) oxygen sensor circuit - "high". The signal from that O2 sensor varies from near 0.0V (lean condition) to near 1.0V (rich condition). If the signal is "out of range" high, or if it is higher than the ECM expects - then it can set this code.

    You really want to look at engine data with a decent scantool. With a warmed up engine, normally A/F sensor reads around 3.3V, short and long term fuel trims are "near" 0% (+/- 5%), and O2 reads "around" 0.7V with a good catalytic converter.

    One possible fault, the A/F is bad and "lies" (a little)- fuel trims go to maybe +10%, and O2 reads 0.8 to 0.95V. Still in normal range but sets a P0138- and the problem is the A/F sensor.

    Or something in the O2 sensor is bleeding voltage from the heater circuit into the signal. Scantool shows about 1.25V (the max it can display) and sets P0138- this time it is the O2 sensor.

    Or maybe there's corrosion or damage to wiring somewhere. Almost anything is possible.

    But a blown fuse ain't really on the list for this.

    A fuse problem can cause a U-series comm code, but if it was a fuse, then the car wouldn't run if one of the "major" ecu's (ECM, hybrid control, power mode, etc) couldn't communicate at all.

    Also, the code listing on your post make me think that you're using a scantool like CarScanner, that only talks on the CAN network. Many systems on a Gen2 Prius don't talk to a scantool via CAN. You might have additional codes in other systems that can help in diagnosis.

    I prefer a scantool that reports what systems it can communicate with and which ones have what codes.

    You might want to read this thread that reviews several scantool apps and OBD2 devices. Some can scan all 15-16 systems on a Gen2.

    https://priuschat.com/index.php?posts/3290690

    Posted via the PriusChat mobile app.
     
    #4 mr_guy_mann, May 19, 2023
    Last edited: May 19, 2023
  5. Jake Miller

    Jake Miller New Member

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    I don't remember where I read it, but the tool that I ended up with was an Ancel AD310 OBD2 / EOBD scanner, but I could totally understand if that doesn't cover anything.

    Maybe some other interesting background is that last summer I had a P0101 code or something in that ballpark for the MAF sensor which I removed and cleaned. Haven't had any problems since then, but maybe they are related.

    The engine idles a little bit harder than some other Gen 2s I have driven, so is it a possibility that I have a bit of a misfire that could be tripping the O2 sensor, and the other codes are a different issue entirely? The communication codes are odd because I can still move the vehicle.
     
    #5 Jake Miller, May 23, 2023
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