P0B97

What it means

P0B97 means the hybrid or EV battery control unit has seen the signal from one of its battery voltage sense circuits (labelled 'S') read lower than expected. The circuit could be a cell-block, module or pack voltage measurement, and which one 'S' refers to depends on the model and battery design. The fault is set when the measured voltage stays below the allowed range, which points to a wiring or sensing fault, or a genuinely low voltage in that part of the pack.

Symptoms

• Hybrid system, check hybrid or master warning light on
• Reduced power or the car going into a limp-home mode
• Reduced or unusual electric assist or electric-only range
• State of charge reading erratic or jumping
• Engine running more often than normal on a hybrid
• Car refusing to enter READY mode or failing to start

Possible causes

• Damaged, corroded or loose wiring or connector on the battery voltage sense circuitlikely
• Fault in the battery monitoring or battery control unit's voltage sensinglikely
• Weak or failed cell or module in the high-voltage battery giving a genuinely low voltage readingpossible
• Poor connection at the battery pack's internal sense leads or busbarspossible
• Low 12 V supply or poor earth to the battery control unit upsetting its measurementspossible
• Water ingress or contamination inside the battery pack or connectorsrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting battery state of charge, temperature and pack voltage at the time of the fault.
2. Check the 12 V battery condition and charging voltage, and look for any related low-voltage or communication codes.
3. Review live data for the individual cell or block voltages and compare them with each other. Look for one reading that is much lower or erratic.
4. Visually inspect accessible wiring, connectors and earths for the battery control unit for damage, corrosion, moisture or chafing.
5. Check the manufacturer's data for what sense circuit 'S' refers to on this model and follow its test procedure.
6. Only a technician trained in high-voltage systems should isolate the system using the correct procedure and then check the sense circuit wiring continuity, resistance and connector pins.
7. Have the battery's capacity and cell balance assessed using the manufacturer's recommended method to find any weak module.
8. Clear the code after repair and road test, confirming it does not return and that voltage readings are stable.

How to fix

• Repair or replace damaged wiring, terminals or connectors on the voltage sense circuit.
• Clean and secure poor connections, busbars or sense leads, and dry or seal any area affected by moisture.
• Replace or update the battery monitoring or control unit if its sensing has failed, following the manufacturer's procedure.
• Replace or rebalance the weak battery module or cell block, or the battery pack, where the voltage is truly low.
• Correct 12 V battery or earth problems and recheck the system.

Can I keep driving?

Nearby codes

• P0B96GenericHybrid/EV Battery Voltage Sense S Circuit Range/Performance
• P0B98GenericHybrid/EV Battery Voltage Sense S Circuit High