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I am stumped

Discussion in 'Gen 2 Prius Technical Discussion' started by Desert Flier, Aug 10, 2024.

  1. Desert Flier

    Desert Flier Member

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    Vehicle:
    2005 Prius
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    Hello All. My 2005 Prius has me baffled. I don't even know what to put in the thread title. The car has 209,500 on it. I'm an aircraft mechanic by trade and have more than kept up on the maintenance for this car. At 150,000 miles all cooling pumps, belts, hoses, spark plugs, all fluids, etc were changed. The hybrid battery was also changed about that time due to a few cells starting to show weak charges. I replaced it with an OEM Toyota Panasonic from the dealer. The car has ran great until recently when it started doing a variety of strange things. When it acts up, it seems like it has a hard time figuring out if it should be charging or pulling from the traction battery. The monitor will show as low as one bar and the arrow between the motor and the battery will flip flop back and forth as if it can't decide what it needs to do. Acceleration is poor as you would expect and the transmission feels like it is actually shifting gears when accelerating. It will start out normal from a dead stop and then almost immediately feel like it kicks down trying to accelerate. With your foot is into the pedal the car will eventually reach what ever speed your'e attempting to maintain. Decelerating may or may not charge the traction battery according to the monitor. When the car is acting up the AC blows warmer than normal and the power steering feels weak and requires more muscle to turn the wheel. The headlights also flicker bright and dim like you would see on a police car (regular halogen).

    Using my Techstream I have thoroughly gone through every system and module without finding the slightest hint that something is wrong. Absolutely no codes, sub codes or any errors on the Techstream, dash, or display. Ever. The traction battery is strong and the highest difference between cell charges is about .03V, the 12V battery is brand new (replaced but probably didn't need to). The starting battery maintains about 12.5V overnight and shows 14.3ish when in ready mode. I have checked grounds, plugs, harnesses-pretty much everything I can think of. The inverter pump is running strong. This mostly seems to happen when it is hotter out (I live in the desert) however it's never consistent. Rain and moisture don't seem to make a difference one way or another. Extreme heat 110F+ is about the only time that I might be willing to bet that it may act up and even then it's a crapshoot. Overall it's been acting up less often but still will act up out of the blue. Shutting the car off and turning it back on does not fix the problem.

    On two occasions over two back to back days the engine ran rough like it was misfiring and shook violently with a loud clatter but only for a brief moment. Once it happened immediately after starting and once while driving down the road. Both times by the time I got the hood opened it was running smoothly again. That particular issue hasn't happened for several months now. The engine purrs right along. Burns no oil between changes at 5,000 miles.

    This is throwing for a loop and I'd love to hear your thoughts. If I had to guess I'd say it has something to do with the inverter but being intermittent and throwing no codes I'm hesitant to tear into anything yet. The ONLY thing that I've possibly come up with is that the fins on I the lower part of the condenser have been mashed pretty good from rocks and debris going through the grill and I'm thinking that possibly the lower part of the radiator behind the condenser (which is for the Inverter/Transmission if I understand correctly) is not getting as much airflow as it could. Both fans are running low or high as necessary.
     
    #1 Desert Flier, Aug 10, 2024
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  2. ChapmanF

    ChapmanF Senior Member

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    Vehicle:
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    IV
    Do you have one of the kind of OBD-II device or smartphone/tablet app that you could stick on the dashboard and watch the various temperatures (battery, MG1 inverter, MG2 inverter, MG1, MG2, etc.)?
     
    #2 ChapmanF, Aug 10, 2024
  3. PriusCamper

    PriusCamper Senior Member

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    Vehicle:
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    Two
    Look inside the battery ECU next to the pack for signs of corrosion. That usually solves the symptom of the number of bars of charge on the pack suddenly dropping because the corrosion sends bad readings to the vehicle computers. Once the computer thinks the pack is down to one bar it creates the symptoms you're describing, which is using almost all engine and very little electric motor.

    As for the arrows flip flopping directions, that sounds normal, never heard of that being a problem...
     
    #3 PriusCamper, Aug 10, 2024
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  4. Desert Flier

    Desert Flier Member

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    2005 Prius
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    I've actually ran it and watched it on the Techstream. I've recorded live data and gone back and looked at it and never so much as found a hiccup. I just drove it about 10 miles today and it ran flawlessly haha. Ever since I looked at new Hybrid Camry's a few weeks ago it seems to be on its best behavior. So weird...
     
    #4 Desert Flier, Aug 10, 2024
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  5. PriusCamper

    PriusCamper Senior Member

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    It's an intermittent problem at first. Then it shows up as a P3000 error code and if you keep clearing the code while driving it fries the circuit board at the plug socket.
     
    #5 PriusCamper, Aug 10, 2024
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  6. landspeed

    landspeed Active Member

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    This is the key symptom : “When the car is acting up the AC blows warmer than normal and the power steering feels weak and requires more muscle to turn the wheel. The headlights also flicker bright and dim like you would see on a police car (regular halogen)”

    Your car is disabling systems as a ‘last resort’, to prevent destruction of (most likely) the inverter

    The 12v DC-DC converter comes online almost immediately after the car is started (less than 1 second). It powers the headlights, so … the only way the headlights would go dim periodically, would be if the 12v DC-DC converter is deactivating itself periodically, due to overheating (or thinking it is overheating).

    The air con pump has a dedicated circuit in the inverter also, and it is known to deactivate when that circuit in the inverter is overheating. Also, power steering is electric; I don’t know how that is powered, but steering going stiff does suggest the inverter is shutting that off, also.

    So - the car thinks the inverter is overheating, and is trying to protect it. It could be possible that some?all of these symptoms could instead be due to the hybrid battery overheating (or thinking that it is overheating), which would result in the car ‘not using’ the high voltage battery, which would probably be similar to the inverter minimising its workload, causing the above symptoms … but I would definitely consider the inverter cooling system as a suspect here.

    It is possible for the inverter pump to be working fine, but trapped air bubbles in the inverter can reduce cooling to parts of the inverter - this is fairly common after replacing the inverter coolant pump (even if the dealer does it!).

    I have some experience of inverter overheating; my Gen2 Prius inverter pump failed (but didn’t short circuit). It did all the symptoms you have, but only when pushed hard (such as deliberate discharge / charge of battery on an empty road, not realising the pump had failed). It even we tried into a weird protection mode where the engine RPM stayed high, and it was a bit hard to stop (I assume it was routing voltage between the MGs).

    I would recommend checking temperatures of the inverter; this is best done ‘live’. I’m not sure how well Techstream shows the temps; I used a phone with a WiFi OBD2 reader, and saw the temperatures going up, then realised the pump had failed. Doing a test drive with screen recorder on a phone / tablet connected to OBD2 can be invaluable here.

    The battery might also be involved - is the battery fan going full blast when the car plays up? My OBD2 reader can show the battery temp sensors, so hopefully Techstream can also.

    Please do check temperatures when the car is playing up (recording temps is best, and play back once parked up etc).

    The advice to check the battery ECU is also good advice; did you replace the voltage sense loom when you replaced the battery modules/cells? - the voltage sense leads absorb leaked electrolyte from the terminals (all batteries leak!), and this wicks up to the battery ECU connector, and can cause short circuits / fires (usually self contained). It is definitely worth checking the battery ECU voltage sense connector!
     
    #6 landspeed, Aug 11, 2024
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  7. pasadena_commut

    pasadena_commut Senior Member

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    Vehicle:
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    Never heard of this for an OEM pump, but the Dorman that was in our 2007 for a while would in some instances not start when the car did. At all other times it worked well. That was causing mysterious inverter overheating events which could not be (easily) replicated.

    I also note that the OP is from Phoenix, where the current forecast is for >= 105F for each of the next 10 days. A marginal inverter pump could easily find itself on the wrong side of the line in conditions like that. The OP indicates that the inverter pump has 60k miles on it, which is close to the average lifetime for that component.

    Lastly, do check the coolant level in that loop and the pH of the fluid. There could be a pinhole leak or some other problem, and if the level is low, problems will follow.
     
    #7 pasadena_commut, Aug 12, 2024
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