2005 Prius won't start after replacing a bad cell in main battery

You have to press the power button twice with your foot on the brake after reinstalling the HV battery.

 

Wow! How incredibly simple. TY

 

Disconnect the 12v negative for a minute to reset the car. Then try to start again

 

do you have to clear the codes from the computer?
is it bolted down? does the battery ground through the case?

 

If you checked voltage at the main relays on the battery side and on the car side, but had no voltage on either side, then either the fuse in the disconnect has opened or one of the main orange cables is not connected properly. Or....one of the busbars is not making contact and causing an open circuit.

Look at the photo below. With the battery assembled and safety disconnect installed (does not have to be clicked downward for this), place the black meter lead on the battery side of the relay closest to the side of the case. Place the red meter lead on the battery side of the relay near the center of the case. This will measure voltage of the HV battery.

The orange cable attached to the black lead relay connects to the (-) terminal of the module furthest from the ECU section.
The orange cable attached to the red lead relay connects to the (+) terminal of the module closest to the ECU section.
The safety disconnect orange cables connect to module 9 and 10 (block 10) from the ECU side.

The safety disconnect inserts a removable fuse between modules 9 and 10. Removing the safety disconnect breaks the circuit, so similarly, any bad connection between any other two modules will act just like a safety disconnect.

 

So voltages can be progressively checked on down the line til zero reading is obtained and that’s the open ?
And in addition all voltages should be additive up to the open?

 

Yes. If you want to verify continuity for each individual module, you can use an alligator clip to attach the black meter lead to the negative relay and then measure voltage at the (+) side of each module, starting at the module where the negative relay orange cable connects and crisscrossing back and forth to follow the "series" connected modules. Voltage should increment upward each module. If you get to a point on a module where voltage drops to zero, you found an open circuit.

Since the battery is experiencing no current flow in this condition, this doesn't always work well for detecting a bad connection, unless the connection is so bad it is actually an open. Even a horrible connection may still allow full voltage downstream if there is no current flow.
In this instance, with no current flow, it would be easy to find a high resistance connection by merely taking a resistance reading of each busbar by measuring between adjacent (-) and (+) terminals(which are connected together by a busbar). You would want to place the meter leads on the terminal nut or the end of the threaded terminal to ensure the reading was measuring the joint between the nut and busbar.

 

I would think that a total cleaning of every busbar is required even if only one module reads bad. It’s very likely that more modules are on their way out. Not using a torque wrench on each and every connection could cause problems, a added resistance in each connection could amount to hundreds of additional ohms and a considerable drop in voltage out. Probably the addition of conductive grease would help too, after battery corrosion removal. But you are right, that fuse you mentioned is probably the culprit.

 

the orange safety plug is also a fuse, have you checked it? im sure theres a youtube video somewhere on how to do it