Replaced hybrid battery 7/2025. Big red triangle today.

The red triangle can be anything, you can go to a local Auto supply (autozone or O'reilly) and they should be able to scan it for free. You should first check the oil level, make sure that's good.

If you've replaced the batteries with new batteries, that should not be an issue.

 

... and in relation to the big hybrid vehicle (HV) battery in behind the rear seat, we mean a factory brand new battery supplied by Toyota, not a new to you recondition/remanufactured/rebuilt/re-anything battery. The latter are a crap-shoot; the former is the most reliable option.

 

Did it start normally, engine ran, or just at a standstill with the warning?
Do you have a digital multimeter? If so you can get some idea of the 12 volt battery’s condition,

how’s the hybrid battery’s state-of-charge indicator behaving, about the usual, or?

notice any changes in the car’s performance/sound, or how easy it goes into electric-only propulsion?

 

The red triangle (master warning light) means there is a problem with the hybrid drive system. So it could be a lot of things, like the hybrid battery, brake system, inverter assembly, electric drive motors, etc.

You need to read the trouble codes to determine the problem.

 

I would not throw any more money at a 21 year old car

 

I would throw some cheap parts at it though. Since the car has a new Hybrid battery and I'm sure that wasn't cheap

 

if you can diy it, absolutely

 

Reading the trouble codes really is the key. The red triangle comes on for around 200 different reasons, and that's too many possibilities to get very far by guessing "I wonder if it could be this?".

Not all scan tools can read the Prius hybrid system codes. If you go to a place like Autozone and they put their scan tool on and tell you there aren't any codes (and yet the triangle is lit), then you just need to someplace with a better scan tool and find out what the trouble codes are. (Don't just add to the many threads where that happened to somebody and they come here and post "I have the triangle lit and no codes".)

There's a fun thread around here from some time recently where somebody wanted to argue with my 200-possibilities figure for reasons that light comes on. They thought I was exaggerating.