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DTC codes / P0Bxx · Hybrid propulsion / P0B91

P0B91Hybrid/EV Battery Voltage Sense R Circuit Range/Performance

P0B91 indicates that the hybrid or electric vehicle battery pack's voltage sensing circuit for the 'R' module or cell group is reporting a voltage reading outside the range the control module expects. The battery energy control module compares the sensed voltage against calculated limits and flags a performance fault when the signal is implausible, erratic, or stuck within a key cycle.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the hybrid system warning light or service vehicle soon message
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Reduced electric-only range or the vehicle refusing to enter EV mode
  • Gauges or dash displays showing erratic or blank hybrid battery state of charge
  • Powertrain derangement with limited power output or forced engine-only operation
  • Possible no-start condition if the battery pack voltage is misreported as critically low

Common causes, most likely first

  1. Faulty voltage sensing harness or connector at the battery module, including corrosion or loose pins
  2. Open or high-resistance sense wire between the battery cell group and the control module
  3. Failed battery energy control module or voltage sensing interface circuit
  4. Internal battery module fault causing an actual out-of-range voltage that the sense circuit correctly reports
  5. Water intrusion or debris in the battery pack connector causing intermittent signal loss
  6. Software calibration issue in the battery control module requiring reprogramming

How to diagnose and fix it

  1. Retrieve all stored codes and freeze-frame data, then clear codes and test-drive to confirm whether P0B91 returns immediately or only under specific conditions
  2. Inspect the battery pack sense harness and connectors for corrosion, loose terminals, chafing, or water intrusion, repairing as needed
  3. Measure resistance and continuity of the R circuit sense wire from the battery module connector to the control module, comparing to factory specifications
  4. Back-probe the voltage sense signal at the control module and compare it to a known-good reference or scan-tool live data to identify a skewed reading
  5. Check for technical service bulletins or calibration updates for the battery energy control module and reprogram if applicable
  6. If the sense circuit and module are intact, perform a battery module voltage measurement to determine whether the cell group itself is out of balance or failing
  7. Replace the faulty battery module, sense harness, or control module as indicated by the test results, then clear codes and verify the repair

Sense circuit faults often mimic battery failure

  • A loose or corroded sense connector can set P0B91 without any real battery degradation, so always inspect the harness before condemning the pack
  • The code can be set by a momentary glitch during a key cycle, and a single occurrence may not indicate a hard failure requiring immediate repair
  • Technicians sometimes replace the entire battery pack when only a small sense wire or connector is at fault, so verify the circuit end to end first
  • High-voltage battery sense circuits are sensitive to water intrusion from clogged pack vents or damaged seals, which may not be obvious from the driver's seat
  • A weak 12-volt auxiliary battery can cause erratic module behavior and false voltage-sense codes, so check system voltage stability before deep diagnosis

Can I keep driving with P0B91?

The vehicle may remain drivable with reduced electric performance, but continued driving risks a sudden loss of power or a no-start if the battery state of charge is misreported. Avoid long trips and heavy electrical loads until the fault is diagnosed, and do not attempt to service high-voltage battery components without proper training and equipment.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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