P0B8D

What it means

P0B8D means the hybrid or EV battery control unit saw the signal from voltage sense circuit 'Q' of the traction battery read lower than the expected range. This usually points to a fault in the sensing circuit (wiring, connector or sensing electronics) rather than the battery actually being at that voltage. Which cell block or module 'Q' refers to depends on the model and battery design, so check the manufacturer data for that vehicle.

Symptoms

• Hybrid or EV system warning light or malfunction message on the dashboard
• Reduced power or the car going into a limited-performance mode
• Poor or no electric assist, or the engine running more than normal on a hybrid
• Inaccurate or fluctuating state-of-charge reading
• Reduced electric range or charging problems
• In some cases the car will not go into Ready mode

Possible causes

• Damaged, corroded or loose connector or terminal on the battery voltage sense circuitlikely
• Open circuit, short to ground or chafed wiring in the voltage sense harnesslikely
• Faulty battery monitoring or cell sensing module/boardpossible
• Genuinely low cell or module voltage from a weak or failing battery sectionpossible
• Poor connection at a high-voltage busbar or sense lead attachment pointpossible
• Fault in the battery control unit or outdated software where the manufacturer has a known issuerare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting battery state of charge, temperature and voltages when the fault set
2. Check for other battery, cell balance or insulation codes that could point to a common cause
3. Follow the manufacturer's high-voltage safety procedure, and leave any work on the battery to a suitably trained technician
4. Visually inspect the battery sense harness and connectors for damage, corrosion, moisture, heat marks or looseness
5. Compare live individual cell or block voltages against the specification and look for one reading that is much lower than the others
6. Check the sense circuit for continuity, short to ground and resistance against the wiring diagram, with the system safely isolated
7. Check the battery pack for signs of water ingress, previous repair or physical damage
8. Check for any manufacturer service bulletins or software updates relevant to this code on that model

How to fix

• Repair or replace damaged wiring and clean or replace corroded or damaged connectors on the sense circuit
• Refit and secure loose sense leads or busbar connections to the manufacturer's procedure
• Replace the faulty battery monitoring module or sensing board if it is confirmed as the source
• Repair or replace the weak battery module or cell block if the low voltage is genuine, and rebalance as the manufacturer specifies
• Update the battery control unit software only where the manufacturer lists it as a fix for this fault

Can I keep driving?

Nearby codes

• P0B8CGenericHybrid/EV Battery Voltage Sense Q Circuit Range/Performance
• P0B8EGenericHybrid/EV Battery Voltage Sense Q Circuit High