HV ECU vs. Hybrid Battery - Which is bad?

My ECU is seperate, yes. It is behind the passenger side, in the back seat.

Posted via the PriusChat mobile app.

 

Hi Jeff,

I'm curious whether your 12v battery disconnect worked to reset the codes? I have a very confusing situation with my 2006 Gen 2 Prius:
- 3 month ago Hybrid battery failed, and I had to pay to have a brand new one installed
-Toyota also installed a new ECU
- first week, shot up to about 44 mpg
- Suddenly a few weeks later, plummeted to 27 mpg. I was driving the exact same routes in the exact same manner.
- Toyota dealer did a diagnostic check on battery and claimed everything was fine.
-Thanks to the priuschat forum, I noticed that people said when 12v battery is dying they saw a sudden major drop in mpg. I used a simple test and discovered that my 12v battery was indeed shot, which made sense because it was about 5 years old.
-I replaced the 12v battery
- Mileage immediately jumped up to around 40 mpg.
-But again, about a week later it plummeted to 32 mpg. Strangely, my MPG meter on the display jumped around like crazy, even when I drove steady.This is exactly what it did when the HV battery died.
- I noticed that in the city, when accelerating power is very weak and the gas engine is always running at 100% without any assiatance from the HV battery. On the highway, mileage seems to be ok, in the low 40s. But again, when accelerating or driving lower speeds in the city, it is struggling and powered only by the gas engine.

I'm wondering if any of these might be the culprit:
- When Toyota replaced ECU they didn't update software or calibrate it correctly
- When I removed the old 12v battery and installed new one, it caused ECU to lose correct codes/calibration
-Toyota gave me a defective ECU
-

Any advice is appreciated!

 

• There is nothing to calibrate, literally plug and play;
• It does, but it quickly relearns what it needs, and most of it is to do with the engine;
• It is not likely, these tend to be very reliable, but anything is possible.

You may be having something not quite right in the engine. Does the throttle body or MAF need cleaning? Has the car ever had an overfill of oil?

 

Open the inverter coolant reservoir and with the car in ready using a flashlight look in the reservoir and see if the red fluid has good movement reflecting healthy pump circulation.. Should look like it’s boiling. May hav3 a bad inverter coolant pump and it’s not
Making the inverter fail because it’s pretty cool out.

I know the hybrid battery is not bad and either is it’s ecu or the dashboard would light up like a Christmas tree with dtc codes so like dolj said I too suspect engine performance.

At 140000 miles it’s way over due for:

New s spark plugs
New trans fluid
New inverter coolant
New engine coolant
New water pump belt.
Thorough throttle body cleaning not the dealer way which is just a bottle of Techron for $50
But a scrubbing with choke cleaner and rags.

Oh and if it was dealer serviced they adjust tire pressure to door placard. Check tires there probably all low. Pump them up to 38 all around.