P0B73: block 12 rationality requires the block 13 comparison too

P0B73 is assigned to block 12 voltage rationality in GM's hybrid parameter table. The generic voltage-sense L range/performance description is not a complete diagnosis. This monitor checks whether selected block readings make sense relative to the independently reported pack voltage.

Read the row across the page break

The source compares twenty times block 12 voltage with pack voltage, and separately compares twenty times block 13 voltage with pack voltage. Both absolute differences must exceed 70 V. The enable conditions continue onto the following physical page, so stopping at the bottom of the first page loses part of the diagnostic context.

GM specifies 160 failures among 170 samples, taken every 100 ms. That is a sustained plausibility check, distinct from the shorter direct low/high sample filters for this channel.

Account for inhibited testing

The monitor requires RUN mode, the stated low-voltage supply window and more than 200 ms after contactor closure. Active block 12 low/high faults and listed pack-voltage faults inhibit the comparison. Those dependencies should be recorded before a technician treats a missing rationality code as a successful repair result.

Compare block 12, block 13 and pack-voltage data from the same operating period. The table does not establish which reading is wrong, and it does not prove a battery replacement is necessary. Actual battery access requires the applicable high-voltage service precautions and qualified personnel.

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 228 · GM PDF, physical page 229.