P0BB9

What it means

P0BB9 means the hybrid or EV battery control unit has found that the signal from one of the battery voltage sense circuits (designated 'Z') is out of range or does not make sense when compared with other measurements. The control unit compares the reading with expected values, such as neighbouring cell or module voltages and total pack voltage. Which part of the pack circuit 'Z' refers to depends on the model, so check the manufacturer's information for that vehicle.

Symptoms

• Hybrid or EV system warning light or malfunction message on the dashboard
• Reduced power or limp mode
• Poor or reduced electric-only driving, or less regenerative braking
• State of charge display jumping around or reading oddly
• Reduced fuel economy on a hybrid because the battery is used less
• Car refusing to enter ready mode or to charge in some cases

Possible causes

• Faulty or loose voltage sense wiring or connector at the battery pack or battery control unit, such as corrosion or a poor terminal fitlikely
• Faulty cell or module voltage monitoring circuit inside the battery control unit or monitoring boardpossible
• Imbalanced or degraded battery cells or modules giving readings outside the expected rangepossible
• Poor high-voltage busbar or connection contact causing a voltage drop that confuses the sense readingpossible
• Water ingress, contamination or heat damage at the pack's sensing connectionsrare
• Outdated battery control unit software where the manufacturer has issued a known fixrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting any other battery, insulation or isolation, or temperature codes that may point to the same fault.
2. Check for manufacturer bulletins and software updates for the exact model and battery type, and work out which circuit 'Z' refers to.
3. Using the manufacturer's high-voltage safety procedure, and only if suitably trained, isolate the system and visually inspect the sense wiring, connectors and pack seals for damage, corrosion, moisture or heat marks.
4. With live data, compare individual cell or module voltages and total pack voltage, looking for one reading that is out of line or jumping.
5. Check the battery temperature readings and cooling system operation, as heat can distort readings and speed up degradation.
6. Check the low-voltage supply and earths to the battery control unit, as poor supply can cause false readings.
7. Wiggle-test the harness while watching live data to find intermittent faults.
8. Run the manufacturer's battery health or balance test to see whether the pack itself is at fault.

How to fix

• Repair or replace damaged sense wiring or connectors and clean any corrosion, following the manufacturer's procedure.
• Tighten or repair poor high-voltage connections, using a trained technician and proper isolation.
• Replace the faulty monitoring board or battery control unit if the diagnostics confirm it has failed.
• Rebalance or replace the affected battery modules or the pack if the cells are degraded or out of range.
• Update the battery control unit software if an applicable update exists for the vehicle.
• Dry out and reseal the pack area and fix the source of any water ingress, then clear the code and road-test.

Can I keep driving?

Nearby codes

• P0BB8GenericHybrid/EV Battery Voltage Sense Z Circuit
• P0BBAGenericHybrid/EV Battery Voltage Sense Z Circuit Low