P0B42

Code

Generic P — Powertrain

Hybrid/EV Battery Voltage Sense B Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 63 RU: 32

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Page language: EN

Causes

Open or shorted wiring in the voltage sense B circuit
Corroded, loose, or damaged connector at the voltage sensing module or BMS
Faulty voltage sense module or sensor (B channel)
Blown fuse or failed reference supply to the sense circuit
High resistance connection or poor ground affecting the sense circuit
Battery pack or submodule failure causing an actual low pack voltage reading

Symptoms

HV system warning light(s) and message(s) on the instrument cluster
Hybrid/EV system may enter reduced-power or limp-in mode
Inability to start in EV mode or disablement of charging/discharging
Possible loss of regenerative braking or altered drivability
Intermittent or permanent fault depending on wiring/connector condition

What to check

Read freeze frame and live data from the BMS/scan tool: compare voltage sense B to sense A and to total pack voltage
Check for additional related codes (BMS, isolation, CAN communication)
Visually inspect wiring harness and connectors for damage, corrosion, or water ingress near the battery and junction points
Verify fuses/relays and supply voltages to the voltage sensing circuits and BMS
Measure the voltage at the sense B connector with the safe vehicle procedures and HV system deactivated as required by manufacturer
Perform continuity and resistance checks on the sense B wiring back to the BMS

Signal parameters

Sense circuit type: typically a low-voltage signal derived from a resistor divider tied to high-voltage pack voltage (vehicle-specific scaling)
Typical measurement module input range: 0–5 V (exact scaling is vehicle dependent)
Low-signal condition: sense B voltage near 0–0.5 V indicates 'low' (thresholds are manufacturer-specific)
Normal proportional range: nominal sense voltage will scale with pack voltage (compare channel A vs B for consistency)
Pack voltage examples (vehicle dependent): common HEV/EV packs often range from ~100 V to 800 V; always consult vehicle data for exact values

Diagnostic algorithm

Retrieve freeze frame, stored DTCs, and live data from the BMS/ECU. Note pack voltage and both sense channel values.
Clear codes and perform ignition cycles to see if code returns; monitor if intermittent.
Visually inspect connectors, pigtails, and harness routing for chafing, heat damage, moisture, or corrosion around the battery and sensing modules.
With HV system disabled and following safety procedures, disconnect the sense B connector and inspect pins for corrosion, bent pins, or water contamination.
Measure the sense B signal at the connector with the vehicle in the appropriate state (follow manufacturer safety steps). Compare to sense A and expected scaling. If sense B remains low at the connector, suspect upstream wiring or sensor/module.
Perform continuity and resistance checks from the sense B connector back to the BMS, checking for shorts to ground or open circuit.
Verify reference supply (e.g., 5 V) and ground for the sensing electronics. Check related fuses/relays.
Check BMS/VCU for internal faults and CAN communication integrity. If harness and supplies are OK, consider replacing the voltage sense module or associated board per manufacturer procedure.
After repairs, clear codes, perform insulation and HV safety tests if any HV work was done, then recharge (if applicable) and road test to confirm the fault does not return.
If problem persists, consult manufacturer service information and technical service bulletins for module updates or known issues.

Likely causes

Damaged harness or pin pushed out at the sense B connector
Contaminated or corroded connector making intermittent contact
Failed voltage sense board or resistor divider in the battery management system
Missing or open reference supply (e.g., 5 V reference) for the sensing circuit
Actual HV battery pack imbalance or an isolated cell/string fault

Fault status

⚠️ Status

Hybrid/EV battery voltage sense circuit B reports low voltage. HV system may be limited; inspect sense wiring, connectors, fuses, and BMS.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.5-4.0 hours

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