Diagnostic article Generic OBD-II
P0B42: The block-two low monitor requires block three to be low as well
Understand the GM P0B42 paired low-voltage criterion before interpreting it as an isolated block-two failure.
Read before applying this article
Documented application
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.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0B42 is the block-two circuit-low code in this GM battery-sensing table. The actual failure condition requires block two below 2V and block three below 2V. A diagnosis based solely on the block named in the code title would leave out a documented requirement.
The pair is the distinguishing evidence
The two conditions are connected by AND. The controller then uses 15 failing samples out of 20 at 100ms intervals. Run mode, an acceptable low-voltage supply and absence of P0A1F are also required.
This paired rule differs from block one's direct low-signal check. It should not be generalized into a universal statement that every battery low-voltage code evaluates only its named channel.
Keep both values and avoid topology guesses
Capture block-two and block-three readings simultaneously, plus their status and companion codes. A combined low pattern may guide the applicable service procedure, but this source alone does not prove a shared connector, common wire or specific sensor-board defect.
The printed threshold is a signal-range criterion, not proof that either physical block is electrically safe or fully discharged. The table provides no approved measurement terminals or pack repair instructions. A qualified high-voltage technician must use the matching sensing diagram and prescribed isolation and verification process before investigating the physical circuit.
The pair requirement is part of the calibration, not a physical wiring diagram.
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 222.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Hybrid/EV Battery Voltage Sense B Circuit Low
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT