P0BAB

What it means

P0BAB means the hybrid or EV control unit has seen the voltage on the battery voltage sense circuit labelled 'W' read lower than the expected range. The control unit uses these sense readings to monitor the high-voltage battery, so a low reading can come from a real fault or from a fault in the measuring circuit. Which cell group, module or sensor 'W' refers to depends on the model, so check the manufacturer's data.

Symptoms

• Hybrid or EV system warning light on the dashboard
• Reduced power or limp-home mode
• Reduced or no electric assist, or the engine running more than normal on a hybrid
• Inaccurate or fluctuating battery state-of-charge reading
• Reduced EV range or poor charging
• Car refusing to enter Ready mode or failing to start

Possible causes

• Wiring or connector fault in the voltage sense circuit, such as a loose, corroded or open-circuit terminal or a short to groundlikely
• Fault in the battery monitoring unit or cell sensing board that measures the voltagelikely
• Genuine low voltage in a cell group or module from an imbalanced or degraded batterypossible
• Poor contact at a high-voltage battery pack connector or busbar sense tap, which depends on the modelpossible
• Low 12 V supply or poor earth to the battery control unit causing false readingspossible
• Fault inside the hybrid or EV control unit, or an outdated calibration where the manufacturer has issued an update for this coderare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, and note any other battery, insulation or 12 V codes that point to a common cause.
2. Check the 12 V battery voltage and its earth connections, as low supply can cause false sensing faults.
3. Look up the manufacturer's data for what sense circuit 'W' refers to on this model, and check for technical service bulletins or calibration updates.
4. Compare live data for individual cell group or module voltages and look for one reading that is much lower than the rest or reads zero.
5. Visually inspect the accessible wiring, connectors and sensor harness for damage, water ingress, corrosion or chafing, without touching any high-voltage components.
6. Have a suitably trained technician isolate the high-voltage system following the manufacturer's procedure, then check sense circuit continuity, resistance and shorts to ground against the wiring diagram.
7. Check the battery pack's balance and capacity using the manufacturer's test procedure to tell a real low-voltage cell group from a sensing fault.

How to fix

• Repair or replace damaged wiring and clean or replace corroded connector terminals in the sense circuit.
• Replace the faulty battery monitoring unit or cell sensing board if the fault is confirmed in the measurement electronics.
• Rebalance, repair or replace the affected battery module or pack if the low voltage is genuine.
• Restore a good 12 V supply and earth by charging or replacing the 12 V battery and repairing poor connections.
• Apply an updated calibration to the control unit only if the manufacturer lists it as a fix for this fault, then clear the code and road test.

Can I keep driving?

Nearby codes

• P0BAAGenericHybrid/EV Battery Voltage Sense W Circuit Range/Performance
• P0BACGenericHybrid/EV Battery Voltage Sense W Circuit High