P0B7B

What it means

P0B7B means the hybrid or EV battery control unit has seen an intermittent or erratic signal on voltage sense circuit 'M'. This is one of the circuits that monitor the voltage of a battery cell group or module. The reading dropped out, jumped or did not match the neighbouring circuits or the total pack voltage. Which cells or module 'M' refers to depends on the model and battery design, so check the manufacturer's data.

Symptoms

• Hybrid or EV system warning light, often with the main malfunction light
• Reduced power or limp mode
• Reduced electric assist or lower EV range
• Hybrid system failing to start (Ready mode not available) in some cases
• Fault that comes and goes with vibration, temperature or road bumps
• Battery charge level display jumping or behaving oddly

Possible causes

• Loose, corroded or damaged connector on the battery voltage sense harnesslikely
• Damaged or chafed sense wiring, or a poor crimp or open circuit in the sense leadlikely
• Poor connection at the battery module or busbar sense tap, such as a loose terminal or corrosionpossible
• Fault in the cell monitoring circuit or sensing board in the battery packpossible
• Failing battery control unit or its internal measuring circuitrare
• Weak or imbalanced cell group causing erratic readings, or coolant or moisture ingress in the packrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data. Note whether other battery voltage sense or cell balance codes are present, and when the fault set (load, temperature, vibration).
2. Check for manufacturer service bulletins and known battery pack issues for this model and year.
3. Only a technician trained in high-voltage systems should go further. Follow the manufacturer's procedure to isolate the high-voltage system and wear the correct protective equipment.
4. Inspect the battery pack sense harness and connectors for damage, corrosion, moisture, bent pins and poor locking, with the system safely isolated.
5. With the system isolated, check the sense circuit for continuity, resistance and short circuits against the wiring diagram. Wiggle-test the harness while watching live data.
6. Compare live cell group or module voltages in scan data, looking for 'M' dropping out, spiking or differing from its neighbours.
7. Check the battery pack for signs of water ingress, physical damage or loose busbar connections.
8. If the wiring is sound, check the control unit's power and earth supplies, and consider the sensing board or battery control unit.

How to fix

• Clean, repair or replace faulty connectors and terminals on the sense circuit
• Repair or replace the damaged section of sense wiring, using the approved method
• Re-secure or repair loose sense taps or busbar connections as the manufacturer specifies
• Replace the faulty cell monitoring board or battery module sensing part if the manufacturer allows it
• Replace or update the battery control unit if the manufacturer confirms it is faulty or has an applicable software update
• Clear the code after repair and road test to confirm it does not return

Can I keep driving?

Nearby codes

• P0B7AGenericHybrid/EV Battery Voltage Sense M Circuit High
• P0B7CGenericHybrid/EV Battery Voltage Sense N Circuit