Replacing 4 cell pack

[vh2q]

About to drop the battery to replace a bad cell. It is one of the cells in a 4 cell pack so i plan to replace the entire module. Could not buy just one cell. Question: is the replacement 4 pack plug and play or am i going to get into an eprom nightmare?

[coulomb]

You will encounter problems unless
* You are lucky and the replacement block of 4 cells has the right CMU id. Since there are only two 4-cell blocks in the pack, I figure that your chances are about 50%, or
* You have a scanner that can emulate a MUT-III and issue the magic command to renumber the CMU ids.

[pbui19]

how do you plan to bring the new cell module to more less the same SOC as the rest in series ?

[vh2q]

The replacement pack is at 16v. The rest of the traction battery is fully charged. So they are all circa 4V. The balancing function will level it all out, I hope. The bad pack I have one cell that is about 3.6V and another about 4v when the rest of them are at full 4.1V. The BMU shows only 4 bars at full charge due to these two weak cells .. it shuts the car down to protect the weakest cell.

[vh2q]

What is the consequence of guessing wrong when switching out the 4 cell module?

[coulomb]

What is the consequence of guessing wrong when switching out the 4 cell module?

My guess (and it's only a guess, I have no direct experience with this) is that the battery will refuse to work (can't go to ready), and you'll get a DTC about non-responding CMU or the like.

Edit: but you could swap the CMU boards in that case. A lot of work once the battery is reassembled.

[Tiborx8]

Why not change only the two bad cells?