P0BB5

What it means

P0BB5 is a generic code meaning the hybrid or EV control unit has seen the signal from one of the traction battery voltage sense circuits (the one labelled 'Y' by the manufacturer) at a level lower than expected. The unit compares the sensed voltage against its expected range and against other voltage measurements. The fault could be in the sensing circuit, its wiring or connectors, or the battery monitoring hardware. Which circuit 'Y' refers to, and the exact set conditions, depend on the model and battery design.

Symptoms

• Hybrid or EV system warning light and/or malfunction indicator lamp on
• Reduced power or limp-home mode
• Reduced or erratic state-of-charge reading
• Reduced electric-only range, or the engine running more than usual on a hybrid
• Car refusing to go into Ready mode, or the high voltage contactors not closing
• Poor charging, or charging stopping early

Possible causes

• Wiring or connector fault in the battery voltage sense circuit (high resistance, corrosion, a loose terminal or a short to ground)likely
• Faulty battery monitoring or voltage sensing module or board within the traction battery packlikely
• Genuine low cell or block voltage caused by an imbalanced or degraded battery modulepossible
• Damage to the sense harness from water ingress, vibration or previous repair workpossible
• Fault in the battery control unit or hybrid control unit, or outdated software where the manufacturer has issued a fixrare
• Low 12 V supply or poor earth to the battery control unit causing false readingspossible

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting any related battery, insulation or contactor codes.
2. Check the 12 V battery condition and charging voltage, as a weak supply can cause false voltage faults on many systems.
3. Inspect the traction battery's external connectors, harness routing and the pack's cooling intake for damage, moisture, debris or corrosion. Do not open the high voltage pack unless trained and qualified.
4. Using live data, compare the individual block or cell voltages and the total pack voltage. Look for one reading that is much lower than the others or implausible.
5. Check the model-specific service information for which circuit 'Y' is, and the expected voltage ranges.
6. With the high voltage system properly isolated by a qualified person, test the sense circuit wiring for continuity, resistance and shorts to ground.
7. Check for technical service bulletins or software updates for the battery control unit on this model.
8. Clear the code and road test, then recheck live data to see whether the fault returns and under what conditions.

How to fix

• Repair or replace damaged wiring, terminals or connectors in the voltage sense circuit.
• Replace the faulty battery monitoring or sensing module, following the manufacturer's procedure.
• Rebalance, recondition or replace the affected battery module or pack where a genuine low voltage is confirmed.
• Repair the 12 V supply or earth faults, or replace a weak 12 V battery.
• Update the control unit software where an outdated calibration is a known cause for this model.

Can I keep driving?

Nearby codes

• P0BB4GenericHybrid/EV Battery Voltage Sense Y Circuit Range/Performance
• P0BB6GenericHybrid/EV Battery Voltage Sense Y Circuit High