P0B57

What it means

P0B57 is the generic definition for Hybrid/EV Battery Voltage Sense 'F' Circuit High. The hybrid control unit or battery monitoring unit saw the signal from one of its battery voltage sensing circuits (labelled 'F') above the expected range. This points to a sensing circuit, sensor or monitoring fault rather than proof of a real over-voltage. Which part of the pack circuit 'F' refers to depends on the model and battery design, so check the manufacturer's data.

Symptoms

• Hybrid or EV system warning light on the dash
• Reduced power or limp-home mode
• Car will not go into Ready mode, or shuts down unexpectedly
• Poor or inconsistent electric assist and regenerative braking
• Hybrid battery charge level display behaving erratically
• Reduced fuel economy as the engine runs more to compensate

Possible causes

• Faulty battery voltage sensing circuit or monitoring module (battery control unit) giving a false high readinglikely
• Open circuit, damaged wiring or poor connection in the voltage sense harness, giving a high signal readinglikely
• Corroded, loose or contaminated connector terminals at the battery pack or monitoring modulepossible
• Short to voltage in the sense circuit from chafed or damaged insulationpossible
• Genuine cell or module imbalance or over-voltage within the battery packpossible
• Outdated or faulty control unit software, where the manufacturer lists it as a known cause for this modelrare

How to diagnose

1. Record all stored codes and freeze frame data, noting any other battery voltage, temperature or insulation codes, and check for manufacturer service bulletins for the model.
2. Check the hybrid or EV battery state of charge and the individual block or cell voltages on a suitable scan tool, and look for one reading that is out of line with the rest.
3. Carry out a visual inspection of accessible harness, connectors and the battery cooling air path for damage, water ingress, corrosion or contamination. Only suitably trained staff should work on high-voltage components, and the system must be isolated and made safe first.
4. With the system isolated, check the sense circuit connectors for pin tension, corrosion and push-out.
5. Following the manufacturer's wiring diagram, test the sense circuit for continuity, short to voltage and short to earth.
6. Compare the monitoring module's reported voltages with measured pack or module voltages, taking all high-voltage safety precautions.
7. Clear the code and road test, then check whether it returns and under what conditions (load, temperature, vibration).
8. If wiring and voltages are good, check whether the manufacturer has a software update or a known fault for the monitoring module.

How to fix

• Repair or replace damaged wiring in the voltage sense circuit.
• Clean, repair or replace corroded or loose connectors and terminals.
• Replace the faulty battery monitoring module or sensing component if it is confirmed to be giving false readings.
• Rebalance or repair the hybrid battery pack, or replace the affected module, if a genuine cell voltage fault is found.
• Apply any manufacturer software update for the control unit if it is a documented cause for this model.

Can I keep driving?

Nearby codes

• P0B56GenericHybrid/EV Battery Voltage Sense F Circuit Low
• P0B58GenericHybrid/EV Battery Voltage Sense F Circuit Intermittent/Erratic