P0B40: zero battery readings do not automatically mean dead cells

P0B40 is the battery voltage-sense circuit B member of the cited GM open-sensing family. The diagnostic points to the integrity of voltage measurement. It is not, by itself, a battery-capacity test.

A group of zeros has a different implication

The shared table notes that loss of a sensing chip's individual power line can leave all its affected cell readings at zero. That pattern does not prove that all those cells physically discharged to zero simultaneously. It is a reason for a qualified technician to investigate the measurement system and its power path.

Other family cases compare neighboring cell voltages or assess busbar sensing. The code B label identifies the channel associated with the stored result; it does not assign a unique failure mechanism to B.

Keep supporting faults in the record

Communication losses, cell-balancing faults and internal sensing-module faults affect monitor availability. Clearing those results before recording the complete voltage pattern can remove information needed to distinguish one channel from a shared problem.

The busbar-positive threshold is incomplete in the printed summary, so this article does not invent a numerical instruction for that branch. Physical channel mapping is also outside this document's scope.

Use the matching battery service information and qualified high-voltage procedures. Verification should establish credible readings across the affected group and a completed diagnostic evaluation, rather than rely on a single nonzero value after memory was cleared.

Application limits

Document-level 2015 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.

Source

15OBDG01 Hybrid Diagnostics, physical PDF pages 635, 636.