P0B9F: Sense U open-line evidence is separate from range faults

P0B9F identifies the U sensing circuit in this GM battery monitor. Its open-line logic should not be replaced with a generic low-voltage assumption. The controller examines relationships between measurements and the operating state of the sensing electronics.

Read the pattern before assigning a failed part

A general sensing-line case uses an adjacent-cell difference greater than one volt. For a common power-line case, the documented comparison is greater than half a volt. GM additionally describes an unpowered slave ASIC producing zero readings for all affected cells. A group of zero values can therefore indicate unavailable measurements rather than independently discharged cells.

The relevant open-line observation lasts 600 milliseconds. These values are calibration examples from the cited controller, not universal pack limits or instructions for live electrical testing.

Verify that the prerequisites are satisfied

Specified sensing-module communication, cell-balancing and internal-performance faults must be absent. The secondary protection self-test must not be running, and the appropriate communication-enabled operating state is required. Record those conditions when evaluating whether the fault returns.

A suitable workshop should map U to the actual battery's service information before drawing conclusions about wiring or cell location. This monitor does not select a replacement battery. Some busbar-case wording is incomplete in the original table; that unresolved branch is excluded rather than converted into a guessed troubleshooting rule.

Source and applicability

15OBDG01 Hybrid Diagnostics, cited controller and monitor only. Historical calibration limits are not universal specifications; per-code vehicle, engine and hardware applicability must be verified.

GM source, physical page 635 · GM source, physical page 636.