P0B87: block 16 rationality requires valid supporting measurements

P0B87 is a plausibility diagnosis for block 16 voltage sensing in GM's hybrid table. The generic voltage-sense P performance name describes the category, while the source shows that the controller checks a relationship between block and pack values.

Follow the paired arithmetic

The absolute difference between twenty times block 16 voltage and total pack voltage must exceed 70 V. The same requirement applies to the block 17 calculation. Both errors are necessary in the published row.

The failure counter is 160 out of 170 samples, taken at 100 ms intervals. This is not the fifteen-of-twenty filter used for this channel's low and high circuit faults. A single inconsistent data point cannot demonstrate the whole P0B87 condition.

Identify why the monitor might be absent

GM requires a valid block 16 input, BPCM RUN mode and more than 200 ms after the contactors close. The source also excludes active block-circuit and pack-voltage faults. Those conditions can prevent a rationality test from running while another sensing problem is already identified.

Use simultaneous block 16, block 17 and pack data to discuss the discrepancy. The code does not say which signal is wrong or prove that a battery block is worn out. Verification and any physical high-voltage investigation must follow the exact vehicle's hybrid diagnostic information and appropriate professional precautions.

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 231.