Prius 2007 - Failed ECU likely culprit for Hybrid Battery

I've got a 2007 Prius with 81,000 miles on it. The motor would not turn on. The Triangle of Death and other warning lights came on. The car was towed to the local Toyota dealership that said the hybrid battery had to be replaced. I had the car towed back to my house.

I disassembled the back of the car and took the hybrid battery out. I used a multi-meter and every single cell was 7.61v. There was corrosion on the bus bar connectors so I cleaned them with vinegar and a steel brush, rinsed with water, dipped in a baking soda slurry, rinsed in water, dried, steel wool cleaned again, covered them in dielectric grease and reattached to the battery.

I disassembled and cleaned the fan even though there was no debris.

The 12 volt battery was replaced with a new one last year.

The Prius still won't start and has the bad lights.

Am I correct in assuming it is the ECU that needs to be replaced. The local Toyota dealership wants $179 to provide me with any diagnostic read out.

I would appreciate any help.

 

Thanks for your replies.

The orange safety plug was, and has been, reseated properly for each removal/reinstallation of the hybrid battery.

When I reconnect the 12v battery and the orange safety plug the car starts up with no error lights. Each test drive lasts for exactly 10 minutes before the Master Warning Light (red triangle), Brake system warning light (orange), and Vehicle stability control light (orange). So far there have been 3 test drives: one with no air conditioning, one with air conditioning on for the entire drive (no change in air conditioning level, engine noises, etc.), and one with turning on the air conditioning 3 minutes into the drive.

When I turn off the car and then try to power on I get the full bad christmas tree lights with no power, no engine: Master Warning Light (red triangle),Slip indicator light (orange), Brake and Brake system warning light (orange), Anti-lock brake system light (orange), Vehicle stability control light (orange), and Malfunction indicator lamp (orange)

Regarding the toyota dealership I first went to. The service desk person did not charge for any diagnostics but said that it was the hybrid battery. When I asked what the diagnostic code(s) were he & the technician couldn't find the printout.

I am trying to avoid buying a generic obdII scanner because I have no intention of doing any vehicle maintenance work beyond the critically necessary.

The reason I think it might be the ecu is by process of elimination of the "other pieces" (cell voltages within 0.1v of each other, clean blower, clean connections, shows warning lights exactly 10 minutes into the test each time.)

I would appreciate any other thoughts or tests I can do. Thanks.

 

Does anyone know of an exact step-by-step guide to:

• making your own working load tester for a Gen2 HV battery cell;
• exact components and how to attach them to each cell;
• load level (amp per hour);
• time frame for applying load?

I believe the ECU is the culprit, but I would like to definitively rule out any potentially "bad" cells. The OCV for each of the 28 cells is between 8.13v and 8.11v. The conditions for getting the triangle of death has not changed after a dozen test runs.

1. Connect 12v battery.
2. Connect HV battery [orange safety plug]
3. Engine starts (No dashboard warning lights).
4. Drive
5. After exactly 10 minutes Triangle of Death lights (time frame is not affected by lights, ac, radio being on or off)
6. Turn off power
7. Unplug HV battery
8. Unplug 12v battery
9. Replug 12v battery
10. Replug HV battery
11. Engine starts (No dashboard warning lights)
12. Drive
13. After exactly 10 minutes Triangle of Death lights (time frame is not affected by lights, ac, radio being on or off)
    
14. ET CETERA

I can't think of any other failure point than the ECU. Any helpful ideas would be appreciated.