P0BB8

What it means

P0BB8 is a generic code meaning the hybrid or EV control system has detected a fault in the circuit that measures one of the high-voltage battery's voltage sense channels, labelled 'Z'. The battery control unit compares the sensed voltage with expected values or other sensors and sets the code when the signal is out of range, missing or implausible. Which battery cell group or measuring point 'Z' refers to depends on the vehicle, so check the manufacturer's information.

Symptoms

• Hybrid system or master warning light on, often with the check engine light
• Reduced power or limp mode
• Car will not go into READY mode or will not start in electric mode
• Poor or erratic battery state-of-charge display
• Reduced electric-only range or the petrol engine running more than usual
• Charging not starting or stopping early on plug-in or electric models

Possible causes

• Damaged, corroded or loose wiring or connector in the battery voltage sense circuitlikely
• Fault in the battery monitoring or battery control unitpossible
• Imbalanced or failing cell group or module in the high-voltage battery giving a voltage reading outside the expected rangepossible
• Poor connection at a busbar or sense lead on the battery packpossible
• Moisture ingress or physical damage to the battery pack or harness, for example after an impact or floodrare
• Outdated control unit software where the manufacturer has issued a fix for this faultrare

How to diagnose

1. Record the freeze frame data and read all stored and pending codes, noting any other battery, isolation or communication codes.
2. Check for manufacturer service bulletins and known issues for this model, as the meaning of the Z channel and the test procedure vary by vehicle.
3. Carry out a visual inspection of accessible low-voltage wiring and connectors to the battery control unit for damage, corrosion, water or loose pins. Do not touch orange high-voltage cables or components unless trained and qualified.
4. Using live data, compare the individual cell or block voltages and the total pack voltage, and look for one reading that is out of line or not changing.
5. Check the 12 V battery condition and charging, as a low supply voltage can cause false sense circuit faults.
6. Only if trained and authorised, isolate the high-voltage system following the official procedure, then test the sense circuit for continuity, resistance and short circuits against the wiring diagram.
7. Clear the code and road test while watching 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 sense circuit.
• Clean and secure poor connections at the battery pack, following the manufacturer's procedure.
• Replace the battery monitoring or control unit if testing proves it faulty, and carry out any required setup.
• Rebalance, repair or replace the affected battery module or pack if the cell voltage is genuinely out of range.
• Update the control unit software if an outdated calibration is a known cause for this vehicle.

Can I keep driving?

Nearby codes

• P0BB7GenericHybrid/EV Battery Voltage Sense Y Circuit Intermittent/Erratic
• P0BB9GenericHybrid/EV Battery Voltage Sense Z Circuit Range/Performance