01 The Consequences of Engaging Reverse Gear While Moving Forw… • 02 Manual Transmission Stalling: Solved! • 03 How a Failed Deal With Honda Pushed Nissan Into Toyota’s Ar… • 04 People Left Concerned After Learning Why Some Hybrids Rando… • 05 How Cold Weather Affects Your Car Battery • 06 This Is Why Your Car Randomly Shakes At Idle Even Without W… • 07 These Simple Car Maintenance Hacks Have Never Been This Easy • 08 Shady Secrets: What Mechanics Won't Tell You About Your Car • 09 P0420 Code Explained: Catalyst System Efficiency Below Thre… • 10 How Far Can You Drive a Car with a Cylinder Misfire? •

DTC codes / P0Bxx · Hybrid propulsion / P0B85

P0B85Hybrid/EV Battery Voltage Sense O Circuit Intermittent/Erratic

P0B85 indicates that the hybrid or electric vehicle battery pack's voltage sensing circuit for the 'O' position is reporting an intermittent or erratic signal to the battery energy control module. The computer detects this when the voltage reading from that specific sense circuit jumps, drops out, or otherwise fails to remain stable within the expected range during normal operation.

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

Symptoms you may notice

  • Illumination of the hybrid system warning light or check engine light
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Reduced electric-only driving range or the vehicle refusing to enter EV mode
  • Sudden loss of power or a 'limp home' mode if the erratic signal triggers a protection strategy
  • Inconsistent state-of-charge readings on the dashboard gauge
  • Possible failure to start or charge if the battery management system cannot trust the voltage data

Common causes, most likely first

  1. Loose, corroded, or damaged electrical connector at the voltage sense circuit or battery module
  2. Chafed, pinched, or open wiring in the voltage sense harness between the battery pack and the control module
  3. Internal fault in the battery module or cell group that causes unstable voltage under load
  4. Failing voltage sense circuit board or sensing harness inside the high-voltage battery pack
  5. Poor terminal contact at the battery energy control module connector
  6. Water intrusion or contamination in the battery pack causing intermittent sense signals
  7. Rarely, a faulty battery energy control module itself

How to diagnose and fix it

  1. Perform a visual inspection of the voltage sense wiring and connectors at the battery pack and control module for looseness, corrosion, or damage
  2. Use a scan tool to monitor the live voltage readings for the 'O' sense circuit and compare them with neighbouring sense circuits to confirm the erratic signal
  3. Check service information for the exact pinout and perform a resistance and continuity test on the sense circuit wiring while wiggling the harness to expose intermittent faults
  4. Inspect and clean the battery pack connectors and module terminals, then apply dielectric grease if recommended by the manufacturer
  5. If the wiring and connectors are sound, follow the manufacturer's diagnostic flow to test the battery module or sense circuit board inside the pack
  6. Replace the faulty sense harness, module, or control module only after confirming the fault is internal to that component
  7. Clear the code and perform a road test or drive cycle to verify the repair and ensure the code does not return

Intermittent sense codes hide in the harness

  • A voltage sense circuit can test perfectly fine with a multimeter at rest but still set this code because the intermittent fault only appears under vibration or temperature change, so a wiggle test while monitoring live data is essential.
  • Technicians often replace the entire battery pack when the real problem is a chafed wire or corroded pin in the sense harness, which is a far cheaper fix if diagnosed correctly.
  • This code does not always mean the battery is failing; a poor connection at the control module can produce the same erratic signal and mimic a failing cell group.
  • Some vehicles set P0B85 after a low-voltage event or battery replacement if the learned sense offsets are not reset, so check for related communication or low-voltage codes before condemning hardware.
  • The 'O' circuit designation is position-specific, so swapping sense leads or modules during diagnosis can move the fault to a different code and confuse the root cause if not documented.

Can I keep driving with P0B85?

You can usually continue driving if the vehicle runs normally and the warning light is steady, but avoid aggressive acceleration, heavy electrical loads, and long trips until the fault is repaired. If the vehicle enters limp mode, loses power, or the warning light flashes, stop driving 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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage