P0B7A

What it means

P0B7A means the hybrid or EV battery control unit has seen the signal from voltage sense circuit 'M' sit higher than its expected range. The letter identifies one of the battery's voltage sensing circuits, but which cell block or module it covers depends on the make, model and battery design. The fault is set when the reading is out of range or implausible compared with the other circuits or the total pack voltage.

Symptoms

• Hybrid, EV or battery warning light on the dashboard
• Reduced power or limp-home mode
• Reduced or unstable electric assist or EV range
• Hybrid system may not enter ready mode, or may shut down
• Charge level display jumping or reading inaccurately
• Charging slower than normal or stopping early

Possible causes

• Damaged, corroded or loose connector or terminal on the voltage sense circuit between the battery modules and the battery control unitlikely
• Open circuit or high resistance in the sense wiring or its fuse or link, pulling the reading out of rangelikely
• Sense wire short to a higher voltage source, or chafed or damaged harnesspossible
• Imbalanced or failing battery cell block or module giving a genuinely high voltage readingpossible
• Fault inside the battery control unit's voltage monitoring circuitpossible
• Outdated control unit software where the manufacturer has issued a fix for this faultrare

How to diagnose

1. Only trained technicians with high-voltage training should work on the system; follow the manufacturer's isolation and safety procedure before touching any high-voltage parts.
2. Read all stored and pending codes and the freeze frame data, noting pack voltage, state of charge and temperature at the time the fault set.
3. Check for other battery voltage, cell balance or insulation codes, which point towards a pack fault rather than a wiring fault.
4. Compare the individual block or module voltages against each other and the total pack voltage using live data, to see if one reading is out of line.
5. Visually inspect the battery harness, connectors, and sense lead terminals for damage, corrosion, water ingress, heat marks or loose fit.
6. Check the sense circuit wiring for continuity, shorts and resistance against the manufacturer's wiring diagram once the system is safely isolated.
7. Check the circuit's fuse or link, if fitted, and the supply and earth to the battery control unit.
8. Check for software updates or technical bulletins for the model, and carry out a battery balance or capacity test as the manufacturer specifies.

How to fix

• Repair or replace damaged wiring, terminals or connectors on the sense circuit, and clean up any corrosion.
• Replace a blown fuse or link only after finding out why it failed.
• Rebalance or replace the faulty battery module or cell block if the voltage is genuinely wrong.
• Replace the battery control unit if the monitoring circuit is confirmed faulty, then carry out any required setup.
• Update the control unit software if the manufacturer lists an update for this fault, then clear the code and road test.

Can I keep driving?

Nearby codes

• P0B79GenericHybrid/EV Battery Voltage Sense M Circuit Low
• P0B7BGenericHybrid/EV Battery Voltage Sense M Circuit Intermittent/Erratic