P0B51: Block-five circuit low requires a matching low block-six indication

P0B51 is the block-five voltage circuit-low code. In this GM table, both block five and block six must indicate less than 2V. The code title alone therefore does not identify all of the measurement evidence used by the controller.

The pair must qualify together

The AND condition is evaluated with the battery controller in run mode, a suitable low-voltage supply and no P0A1F fault. Failure requires 15 qualifying samples out of 20 at 100ms intervals.

A block-five value recorded in isolation cannot establish whether this full condition occurred. Preserve the neighboring reading on the same timeline, particularly when an intermittent event has disappeared by the time the vehicle is examined.

Do not infer the wiring arrangement

A paired low pattern may be relevant to the vehicle-specific diagnostic process, but the table does not prove a shared sense wire, damaged connector or failed monitoring board. It also does not establish the actual charge or physical voltage of either block from the code alone.

Keep companion rationality and high-limit records before clearing faults. A qualified battery technician must consult the correct sensing diagram and service tests to determine the cause. High-voltage isolation and verification are required for physical access; low scan readings do not demonstrate that the pack or its internal conductors are electrically safe.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, only the cited controller and monitor. These are historical calibration examples; individual vehicle, engine and hardware applicability is not established. GM PDF, page 224.