P0B90: Voltage sense R is checked under balancing load

P0B90 identifies hybrid/EV battery voltage sense circuit R. In GM's 2018 HPC2/BSM table, the diagnostic detects excessive calculated resistance in that sense line. It is not a general “battery voltage low” code.

Why an unloaded reading may miss it

The monitor deliberately operates cell-balancing gates after normal voltage readings. The resulting current makes resistance in the sensing path visible as a voltage drop. GM converts that drop into a resistance estimate and uses a threshold above 30 ohms for this implementation.

The failure requires seven bad evaluations among nine samples, sampled every 100 milliseconds. System voltage must exceed 10.2 V, and the listed battery-interface communication fault group must be absent. The table assigns Type A, one-trip reporting.

Two consequences of the same sense-path defect

The source explicitly links excess sense resistance to inaccurate cell-voltage sensing and reduced effectiveness of charge balancing. That means a diagnosis based only on a displayed cell voltage can overlook the balancing consequence. It also means the code cannot identify a worn-out cell purely from the reported voltage.

A technician should confirm the exact circuit R mapping and examine the relevant sensing/balancing evidence with valid communications. Letter R is an identifier, not a universal location in every battery pack. Do not open the pack or load a sense wire to imitate this test. Qualified high-voltage service and the correct repair procedure are needed; successful verification includes the monitor's load-dependent result, not just a cleared DTC.

Source and applicability

This explanation follows the documented GM monitor, not a verified application to every vehicle with this code. Confirm the vehicle, reporting module and calibration in current service information. GM diagnostic table, physical page 856.