P0B9B

What it means

P0B9B means the hybrid or EV battery control unit found that the voltage reading from the battery voltage sense circuit designated 'T' is out of range or does not agree with what it expects. The reading may disagree with other sense circuits, the total pack voltage or the expected change under load. Which cell group or module circuit 'T' refers to depends on the vehicle and battery design, so check the manufacturer's data for that model.

Symptoms

• Hybrid or EV system warning light on, often with the main warning lamp
• Reduced power or limp mode
• Reduced or no electric assist, or the engine running more than normal on a hybrid
• Poor or erratic battery state of charge display
• Car won't go into READY mode or won't charge (model dependent)
• Reduced electric range or charging that stops early

Possible causes

• Fault in the voltage sense wiring or connector for that circuit (loose, corroded, damaged or high resistance)likely
• Faulty battery monitoring unit or cell sensing boardlikely
• Imbalanced or weak cell group or module giving a voltage reading that fails the plausibility checkpossible
• Poor connection at a battery module busbar or terminal affecting the sensed voltagepossible
• Damage to the battery pack harness from water ingress, corrosion or previous repair workpossible
• Internal fault in the battery control unitrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting battery state of charge, temperature, pack voltage and whether the car was under load or charging when the fault set.
2. Check for related battery codes (other voltage sense circuits, cell imbalance, pack voltage, insulation) as they help show whether the fault is local to one circuit or pack-wide.
3. Look up which cell group or module circuit 'T' refers to for this model and engine, using the manufacturer's data.
4. Only if trained and equipped for high-voltage work, follow the manufacturer's isolation procedure, then visually inspect the battery pack sense harness, connectors and the pack for damage, corrosion, moisture or signs of previous repair.
5. View live data for the individual cell or block voltages and compare the circuit 'T' reading with its neighbours and the total pack voltage for spread or implausible values.
6. Check connector pin tension and resistance and continuity of the sense wiring against the manufacturer's wiring diagram, wiggling the harness while watching live data for dropouts.
7. Check the busbar and module connection tightness and condition at the affected module, if the manufacturer permits access.
8. If wiring and connections are good, check the manufacturer's procedure for testing the battery control unit and the affected module, and look for any published service information on the fault.

How to fix

• Repair or replace damaged sense wiring or connectors, and clean or treat corrosion following the manufacturer's procedure.
• Tighten or repair poor busbar or module connections to the specified torque.
• Replace the faulty battery monitoring unit or sensing board if testing confirms it is at fault.
• Rebalance, repair or replace the weak battery module or cell group as per manufacturer guidance.
• Dry out and repair the cause of any water ingress, then replace any damaged components.
• After repair, clear the codes, then road test and confirm the code does not return.

Can I keep driving?

Nearby codes

• P0B9AGenericHybrid/EV Battery Voltage Sense T Circuit
• P0B9CGenericHybrid/EV Battery Voltage Sense T Circuit Low