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DTC codes / P0Bxx · Hybrid propulsion / P0B55

P0B55Hybrid/EV Battery Voltage Sense F Circuit Range/Performance

P0B55 indicates that the hybrid or electric vehicle battery pack's voltage sensing circuit F is reporting a voltage outside the expected range or is not performing as designed. The battery energy control module compares the sensed voltage from this specific circuit against the voltages from other sense circuits and the calculated pack voltage, and it sets this code when the signal is implausible, erratic, or out of range.

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 light
  • 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
  • A sudden drop in state of charge displayed on the dash that does not match actual driving conditions
  • The internal combustion engine starting more frequently or staying on longer than usual
  • In rare cases, a message to pull over safely or a reduced power limp mode

Common causes, most likely first

  1. A faulty voltage sense wire or connector at the battery pack, often due to corrosion or vibration damage
  2. A failed cell voltage sensor module or sense harness inside the high-voltage battery assembly
  3. A poor connection or loose terminal at the battery energy control module connector
  4. Internal failure of the battery energy control module affecting only the F circuit input
  5. A weak or failing battery cell that causes the sensed voltage to swing outside the expected range
  6. Water intrusion or contamination in the battery pack causing intermittent sense circuit faults

How to diagnose and fix it

  1. Retrieve all stored codes and freeze-frame data, then clear the code and test-drive to see if it returns immediately or only under specific conditions
  2. Inspect the low-voltage sense harness and connectors at the battery pack for corrosion, chafing, or loose pins, and repair as needed
  3. Measure the voltage on the F circuit at the battery energy control module connector and compare it with the voltage measured directly at the cell group it monitors
  4. Check the service information for the exact resistance and voltage specifications for the F circuit and perform a continuity and short-to-ground test
  5. If the wiring and connectors are good, substitute a known-good cell voltage sensor module or battery energy control module only after confirming power and ground integrity
  6. Perform a battery pack capacity and balance test to rule out a weak cell that is causing the sense circuit to read out of range
  7. After repairs, clear codes and verify the F circuit voltage reading matches other sense circuits within specification during a road test

What the F circuit code really means

  • A P0B55 is often set by a poor connection at the battery pack sense harness rather than a failed sensor, so always wiggle-test the harness while watching live data before condemning any module.
  • The code does not automatically mean the high-voltage battery is bad; a single faulty sense wire can mimic a failing cell and trigger unnecessary pack replacement.
  • Intermittent P0B55 codes that appear only on rough roads or after temperature changes frequently trace back to a chafed wire inside the pack, which a static voltage check will not reveal.
  • Some vehicles set this code when the 12-volt auxiliary battery is weak because the battery energy control module misreads reference voltage, so check the low-voltage system first.
  • A cell voltage sensor that is failing can report plausible but slightly offset readings for weeks before the code sets, so compare all sense circuit values side by side during diagnosis.

Can I keep driving with P0B55?

You can usually continue driving if the only symptom is a warning light and the vehicle otherwise operates normally, but avoid heavy acceleration, prolonged high-speed driving, and deep discharging the battery until the fault is repaired. If the vehicle enters limp mode or displays a pull-over message, stop safely and have it towed to avoid damaging the high-voltage battery.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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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