First time Prius owner - Red Triangle of Death and Limp Mode

So I purchased my first used 2004 Prius (Gen 2) with 192k miles about 4 months ago, and really am in love with it. No major issues except for an airbag light that is always on. Interior/exterior is spotless for its age.

Anyways, the honeymoon phase is over, and it’s time to get down and dirty.

I was driving yesterday, coming to a stop, and out of nowhere the red triangle of death along with the check engine light and ABS light came on. The owner of the car said “you don’t need to worry until you see a big red triangle.” Now I’m worried since I rely on my Prius for gig income at the moment.

I’ve been doing some research online along with my own checks. Here’s the status of the car:

1. MPG: I religiously tracked MPG at the pump, was getting its normal 40/32 MPG leading up to this incident.
2. The HV battery level, as shown on the display screen in the car, was appearing to drain faster than what I initially bought it, but still quite normal BEFORE the red triangle of death appeared. After getting the red triangle, the battery level is now all of a sudden draining to 1 bar within the span of a minute or two, and then showing fully charged after a min or two of stopping/smooth driving.
3. The car at the moment will use the HV for acceleration, but it can be delayed/choppy at times. But I am able to get to 70MPH speeds like normal. Although, if I let the the energy bar dip below 2 bars while driving, then something happens where the car goes into a “limp” mode, and the 4 cylinder engine runs very hard just to barely get it to accelerate to 50 MPH, making it unsafe to drive in limp mode when needing quick acceleration. So it seems the HV turns off and the gasoline engine is the only system running. If I turn the car off, wait a minute, and turn it back on, then I can actually drive it normally again with the HV system engaged, and the bars will display around 3-4, allowing me to drive it again and use regen braking. I don’t have to disconnect the battery to drive it again.
4. The battery fan within the interior of car cabin is always running (I can hear it), whether in limp mode or not (or cold starting it in the morning).
5. I checked the engine coolant level and filled since it was low. I checked the inverter coolant tank, and it is normal level with the pump appearing to work after eyeballing it.
6. Went to AutoZone where they checked the 12V battery, and showing good (13.1V beginning, 12.6V under load)
7. AutoZone checked the ECU codes using their cheap scanner, two codes are popping up (C1259 - ECM Communication Malfunction | C1310 - Malfunction in HV System). I think the ECM code may have already been there with the Airbag light always being on, the C1310 is the new issue.

So with that background, what’s the most likely culprit? A corrupted HV battery cell (or a few)? If this is the case, why am I still able to drive it, and why would the battery level all of a sudden spike so erratically while driving?

And final question, so I have $50 in my bank account and going through job transition, I DoorDash daily so I am under obligation to continue driving this in its current state. What type of risk does this pose to the HV system? I plan on buying a few cells on eBay and replacing them myself when I have the money soon, but until then, is it okay to continue to drive in limp mode, or in semi-limp mode that it’s in now?

Basically, I need to get another 800 miles on this Prius within the next few days while in its current condition. Wondering if instead of me needing to buy 3 bad cells, it’ll require me to buy more replacement cells as the HV battery pack disintegrates rapidly due to the sudden charging/drain spikes.

 

I took a look at that thread and seems interesting. He had many other additional codes, and there was no mention of erratic limp driving that I’m experiencing. AutoZone only found 2 codes on my vehicle. It’s strange I don’t see additional P codes to indicate there are bad blocks/cells.


I’ve never opened the casing to the HV battery, but maybe corrosion or a nut is loose inside the bus terminals. I’ll have to check that for sure when I get tools.

 

I was going to buy this Bluetooth enabled sensor to monitor the health of the individual HV cells, do you think it will also read P codes?


NEXAS NexLink OBD2 Amazon

 

I’m looking for the cheapest option that’ll give me results, not able to afford a $600 techstream device (although I wish I could!).

The app review you linked to mentioned the Dr. Prius App. On the Dr Prius website it recommends the NEXAS NexLink OBD2 Amazon which another user said was not good.

Any ideas?

 

Thanks for recommendations, I will go through them all shortly.

UPDATE: So for the past couple days I’ve been able to DoorDash with it, leaving the car ON all day long mostly. For 2 days, if I didn’t allow the battery to dip below 2 bars, it would operate normally with both the gasoline engine and HV battery working together. I would have to turn off the car and back on only three times throughout the day if it ever entered limp mode, which relied only on the gasoline engine at that point.

But today is a different story. Now, the car will go into gasoline mode if it’s overcharged (if the display shows around 7/8 bars) as well as under 2 bars. So i have to turn on the AC periodically, flip the car into neutral when coming to a stop to prevent overcharging and it going into limp mode. Also important to note, it will go into gas mode if I brake hard, going over bump, brake and turning, or going up very steep hill. Anytime I stop and it goes into limp/gasoline only mode there is also an accompanying beep with the problem symbol on the screen.


When it’s in EV mode, it is able to accelerate normally, so I’m hopeful it may just be be a loose nut, corroded terminal, or similar within the HV battery. I read on this forum that if the HV battery was really failing, then the gasoline engine wouldn’t be running normally?

 

Yes, I’ll buy the scan tool when I can afford it, y’all really don’t know how broke I am right now.

I had enough money to find a complete HV battery pack at a local junkyard down the road from me, which I paid $100 for and will be picking up tomorrow. I’ll be borrowing a friends tools to replace the HV battery unit myself tomorrow which is a simple process according to YouTube.

If this fails, I will probably have to buy the scanner, a voltmeter, and a charge/discharge system and pick out the best cells between each HV batteries and then charge them up appropriately and install it. Then I’ll sell the remaining battery for more than I purchased the junkyard HV pack.

If I receive a dud battery pack from the junkyard, then I might as well just sell my Prius at a loss and move onto the next used car, as has been my life for awhile.

 

Ok, I succeed. Just bought the Autel MaxiAP from Amazon and it’ll be here tomorrow!

I’m sure driving it in it’s current state is doing some unknown damage somewhere, as I noticed an Oil indicator light pop up on the digital display a few times whenever it switches into limp mode.

Also, I don’t think it’s a complete “waste of money,” since I am getting a great deal on the battery. I only bought it for $100 and I can resell it for $200 or keep it as a spare if I have further issues with the HV system down the line. Another local guy who has a properly charged and tested HV battery is selling his for $700, so I’m definitely getting a better deal, especially considering we know for a fact that a high-mileage used Prius will with 100% certainty experience bad blocks occasionally.

 

So glad you posted that. I thought it had something to do with the failing battery alerts.

Took it into the shop today and was low on coolant and oil. I replaced oil just a month ago, and it had less than a quart in it. The mechanics said they didn’t see any visible leaks, and I drove 3,000 miles in a month, so they said it could be burning oil. But doesn’t explain the low coolant since I also filled that up recently as well. Probably a head gasket issue I’m guessing.

Would make sense since I’ve been driving this daily in this condition, and the 1.5 cylinder engine is constantly running at near full power.

 

The scanner arrived today so I’m headed to an area where I’m going to read the codes and then replace battery if that’s what the scanners codes implicate.

I have noticed that the oil light on the digital display is gone, along with the beeping every time I brake. So it was unrelated low oil pressure due to low oil level.

 

Update: The codes that are showing up using the AP-600 are as follows:

P0A80
P3011
P0A80
P3011

They all seem to hint at a bad battery

 

Okay, I just spent 5 hrs swapping the battery in a Walmart pharmacy drive-thru (it was raining) with the junkyard one I found for $100.

I freaked out because when I tried to power on the car it wouldn’t turn over, but there was still 12V power. So I closed all the doors, locked and unlocked the car, and it started up just fine. Been driving it for an hour and no new codes have popped up and it appears to be operating normally. What a freaking relief.

Thanks for the suggestions and the code scanner will come in handy in the future. Wonder where I should sell the bad battery I have, or to just send it to junkyard. It about broke my back lifting that thing by myself.

I’ll probably have to investigate the low coolant/oil issue another time.