P0B68

What it means

P0B68 is the generic code for a fault in the Hybrid/EV Battery Voltage Sense 'J' circuit. The battery control unit or hybrid control unit compares the voltage reported by one of its battery voltage sensing circuits with what it expects, or finds the signal missing, out of range or implausible. Which cell, module or sensing point 'J' refers to depends on the vehicle and battery design, so check the manufacturer's data for the model.

Symptoms

• Hybrid system or battery warning light on, often with the malfunction indicator lamp
• Reduced power or limp mode
• Car will not go to READY mode or will not start in EV mode
• Reduced or erratic electric-only driving and poor fuel economy
• State-of-charge display jumping or reading incorrectly
• Engine running more often than normal to maintain battery charge

Possible causes

• Damaged, corroded or loose voltage sense wiring or connector at the battery pack or battery control unitlikely
• Fault in the battery monitoring or battery control unit's voltage measurement circuitpossible
• Imbalanced or failing battery cells or modules giving a reading outside the expected rangepossible
• Poor connection at the high-voltage battery busbars or service disconnectpossible
• Low 12 V supply or poor earths affecting the control unit's measurementspossible
• Moisture or contamination inside the battery pack or connectorsrare
• Outdated control unit software where the manufacturer has issued a fix for this faultrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting any other battery, cell balance or insulation faults that appear alongside P0B68.
2. Check the 12 V battery condition and charging, as low supply voltage can upset the control units and set false faults.
3. Check for technical service bulletins or software updates for the model and code.
4. Without touching high-voltage parts, visually inspect the accessible low-voltage wiring and connectors to the battery pack and control unit for damage, corrosion, water ingress or loose pins.
5. Using live data, compare the individual cell or block voltages and the total pack voltage, looking for one reading that is out of line or stuck.
6. Have a trained high-voltage technician isolate the system following the manufacturer's procedure, then check sense circuit continuity, resistance and connector tightness against the wiring diagram.
7. Check busbars and service disconnect connections for looseness or heat marks, again only after safe isolation.
8. Clear the code after repair and road test, monitoring the voltages to confirm it does not return.

How to fix

• Repair or replace damaged sense wiring and clean or replace faulty connectors.
• Tighten or replace loose or corroded battery busbar and service disconnect connections.
• Rebalance or replace the affected battery cells or modules as the manufacturer's procedure directs.
• Replace the battery control or monitoring unit if testing shows its measurement circuit is faulty.
• Replace or recharge the 12 V battery and repair poor earths if the supply is at fault.
• Apply a manufacturer software update if one is published for this fault.

Can I keep driving?

Nearby codes

• P0B67GenericHybrid/EV Battery Voltage Sense I Circuit Intermittent/Erratic
• P0B69GenericHybrid/EV Battery Voltage Sense J Circuit Range/Performance