Low Voltage in Rear Power Outlet

Discussion in 'Prime Technical Discussion' started by PiPLosAngeles, Nov 27, 2018.

  1. PiPLosAngeles

    PiPLosAngeles Active Member

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    I have a 300W inverter that powers nothing more than a 60W load while driving. It worked for 5 years in my 2012 PiP, but I can't use it in the 2018 Prime because it constantly shuts off due to low voltage (10.5V). When parked in READY mode it doesn't happen, but when I drive it starts happening so there's no real way for me to get a multimeter on it while it's happening.

    I just wanted to see if other people had experienced any voltage issues with the power outlets in the Prime. I checked the 12V battery and it's at 12.4V when the car has been off overnight.
     
  2. jerrymildred

    jerrymildred Senior Member

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    If it was me, I'd get one of these:

    Get an extension cord for it if you can't find someone to watch it while you drive. See what it does with no other load. Gather data like that with and without a load and then go see the dealer. It should be under warranty.

    Or it may be that the wire feeding it is not big enough to power a 60W load plus the overhead of the inverter itself, which would pull down the voltage, but ought to blow the fuse. Does the manual give a maximum load for the outlet?
     
  3. PiPLosAngeles

    PiPLosAngeles Active Member

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    The 12V outlet is 10A and the inverter draw with 60W load and overhead is just shy of 6A. The 120V outlet shuts down at 2.75A for more than 2.5s (330W). I would think I would have experienced this issue in the PiP if it were something related to the inverter or cable.
     
  4. jerrymildred

    jerrymildred Senior Member

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    Yeah, if it worked in the PiP, it should work in the Prime. I'd head back to the dealer. Might be a poor connection in the wiring causing a voltage drop, and that's a potential fire hazard.
     
  5. PiPLosAngeles

    PiPLosAngeles Active Member

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    Taking some measurements has me more confused. The open circuit voltage of the outlet is 14.2V when the car is in READY. When I place a 6A load on the outlet the voltage drops to 11.4V. What's even more strange is that when I shift into DRIVE the voltage drops further to 10.5V. That's the point where my inverter gets mad.
     
  6. PiPLosAngeles

    PiPLosAngeles Active Member

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    At first I thought it might be that Toyota may have used wire that was too thin, but the only way to get that kind of voltage drop would be to have used something like 24AWG, and I really doubt that it's that bad. I don't know what else could cause that.
     
  7. jerrymildred

    jerrymildred Senior Member

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    A loose connection or bad solder joint could do that as well. Dealer should fix it for free.
     
  8. ChapmanF

    ChapmanF Senior Member

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    If you move your voltmeter to various other spots in the car's electrical system, do you find other spots where shifting to D makes it drop by a volt? That puzzles me.

    -Chap
     
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  9. SteveMucc

    SteveMucc Active Member

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    does it happen on the front outlet as well?
     
  10. PiPLosAngeles

    PiPLosAngeles Active Member

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    It happens everywhere in the 12V system, even at the battery. It's at the dealer now, who's had trouble figuring it out. They're working with Toyota technical support and may need the car the whole weekend. Fourth Toyota and the first time I've ever experienced an issue. Disappointing in a brand-new car, though. The worst feeling is the doubt that will forever be with the car once it's known to harbor electrical gremlins. I'll always be wondering when it's going to malfunction again. :(
     
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  11. bisco

    bisco cookie crumbler

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    agreed. free loaner?
     
  12. ChapmanF

    ChapmanF Senior Member

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    Anybody else's Prime reduce the DC/DC converter output by a volt when shifted into Drive? I wonder if that could be by design. I don't have a ready guess as to why that would be a useful design, but it sounds very deterministic, from the description. Perhaps to charge the aux battery at a higher rate when just sitting around, preserve more power for other purposes when driving.

    Anything about it in the Prime New Car Features manual?

    -Chap
     
  13. PiPLosAngeles

    PiPLosAngeles Active Member

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    I suspect a defective 12V battery that is interfering with the proper operation of the 12V system (maybe an internal short or something). The dealer just called and reported that Toyota has the same suspicion and they're going to try and replace the 12V battery. Murphy's Law in full effect, though, and they didn't have any so it took the whole day to locate one and get it to the shop. I'm supposed to pick it up in an hour or so. I'll keep you posted.
     
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  14. priuscatprimeguy

    priuscatprimeguy Senior Member

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    I have a scanguageII connected with volts as one of my options when car is in ready or drive the voltage is 14.2 volts, when I turn the car off the voltage drops to 12.3 volts, the next morning the battery voltage is at 11.9 volts before I put car in ready mode. It always jumps to 14.2 volts when I put the car in Ready mode or drive mode.:cool:
     
  15. bisco

    bisco cookie crumbler

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    you need a new 12v my friend
     
  16. ChapmanF

    ChapmanF Senior Member

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    Only if I do too, and on my list of things to worry about that's nowhere near the top.

    Rather like the voltage readout on the MFD, the voltage readout on a ScanGauge II is actually what's measured by the ScanGauge itself on the always-hot pin 16 of the diagnostic connector. That's downstream of the battery by several small voltage drops, and if I saw those numbers on mine, any thoughts of imminent battery shopping would be far from my mind.

    -Chap

    Edit: as an exercise, walked right out to my car just now, opened driver door, waited for brake pump to finish, pushed button on ScanGauge, read 11.9 on the nose. Not having any battery-related difficulties and not expecting any. Maybe I'll be wrong....
     
    #16 ChapmanF, Nov 30, 2018
    Last edited: Nov 30, 2018
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  17. PiPLosAngeles

    PiPLosAngeles Active Member

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    I spoke too soon. Went to the dealer to pick up the car and they informed me that they thought the other dealer had the battery, but it turned out to be the wrong battery and that they can't get one for 1 - 2 weeks. No loaner car because theirs are all loaned out already. So I took my car back and found another dealer about 60 miles away that reports having the battery in stock. Will take it to them in the morning.

    The tech's write up reads:

    Customers states low voltage while driving. Tested battery and notice that the battery failed load test. Unfortunately parts doesn't have battery in stock. 5 - 7 working days before part arrives.

    What scares me is that the low voltage happens when in READY mode and when the ICE is running. Unless there is some sort of fault in the battery that's causing the voltage sag, I fear the battery is dead BECAUSE of the 12V system and not the cause of the issue. I can't figure out how the DC/DC converter could be correctly generating 100A of 12V power only to have voltage sag when I draw even 5A with the car running.

    Further experimentation seems to confirm that it's a voltage sag due to load. I can turn on the vent fan and watch the voltage plummet. I can even see it when I push the brake pedal. This is in READY and even with ICE on. I really hope it's not a bigger problem. I suppose I could disconnect the battery after the car is running and see if it cures the problem. If it doesn't I'll be pretty sad.
     
    #17 PiPLosAngeles, Dec 1, 2018
    Last edited: Dec 1, 2018
  18. Elektroingenieur

    Elektroingenieur Senior Member

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    There’s a general explanation of the charging system, as summarized in a previous thread, but nothing quantitative, other than the basic specifications for the auxiliary battery. If the auxiliary battery failed the load test, it should be replaced, of course, but I wonder if the battery state sensor assembly might also be faulty, which could lead to improper control of the DC-DC converter output.

    If I were diagnosing the problem, after replacing the battery, I’d do the complete procedure in the Repair Manual (more info) under Power Source/Network: 2ZR-FXE Battery/Charging: Charging System: On-Vehicle Inspection. I’d also compare the current and voltage measurements during the last steps of that procedure, and a thermometer measurement at the sensor assembly, with the values for Auxiliary Battery Current, Auxiliary Battery Voltage, and Smoothed Value of Auxiliary Battery Temperature, respectively, shown in a Toyota Techstream diagnostic system connected to the car under Powertrain > Hybrid Control > Data List, just to verify that the data reaching the hybrid vehicle control ECU from the sensor assembly are reasonable.

    Sensor faults are supposed to be detected automatically, but the detection limits for the associated diagnostic trouble code (DTC), P058A01, Auxiliary Battery Monitor Module Range/Performance, as listed in the Repair Manual, are fairly loose, and I can imagine that a sensor reading could be wrong enough to cause odd behavior but not far enough out of range to cause the DTC to be stored.
     
  19. PiPLosAngeles

    PiPLosAngeles Active Member

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    In the event of some failure of the battery or battery state sensor assembly, shouldn't that mean the DC-DC converter would start outputting a constant 12V? Shouldn't that mean as I draw more current the DC-DC converter ramps up to keep the voltage constant? Because I'm not seeing a constant 12V I'm really worried that there's a much larger problem. Maybe a sensor is telling the ECU that the 12V battery is full and so the power production never ramps up.
     
  20. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes—though the constant voltage should be closer to 14 V than 12 V, I’d expect—but only if the failure is one that the hybrid vehicle control ECU has been programmed to detect, or if at least one of the other programmed conditions for constant voltage control mode is satisfied.
    Perhaps; that’s the kind of insidious failure I meant to suggest above.
     
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