P0B78: block 13 plausibility involves block 14 and pack voltage

P0B78 is the block 13 rationality code in the cited GM hybrid document. A generic scanner may call this voltage sense M range/performance. The word performance refers here to measurement consistency, rather than a direct assessment of available battery energy.

The calculation is the diagnostic distinction

GM compares twenty times block 13 voltage with total pack voltage. Its absolute difference must be greater than 70 V, and the corresponding calculation for block 14 must also be greater than 70 V. Both comparisons belong to the failure rule.

The controller accumulates 160 failures within 170 samples, with 100 ms between samples. A single unusual displayed voltage does not reproduce that sustained relationship. Record the two block readings and pack reading from the same time period where possible.

Check validity and inhibition

The table requires valid block 13 input, RUN mode and adequate controller supply. It also requires more than 200 ms since the contactors closed and excludes specified block-circuit or pack-voltage faults. Those dependencies can explain why the performance test does not run while another measurement fault is active.

The code does not establish whether the block measurements, pack measurement or underlying battery condition caused the disagreement. That distinction requires the exact vehicle procedure. Do not turn the monitor's multiplication or thresholds into a physical high-voltage test; a qualified hybrid technician must choose the appropriate diagnostic method.

Source and applicability

GM 2010 10OBDG10 Hybrid Diagnostics, cited BPCM or hybrid-controller monitor only. Historical calibration values are not universal specifications; no per-code model, engine or hardware fitment has been established. GM PDF, physical page 229.