Damaged, loose or corroded connector or terminal on the battery voltage sense harness; Open circuit, short or chafed wiring in the sense circuit between the battery cells or modules and the battery control unit; Faulty cell monitoring board or voltage sensing circuit inside the battery pack; Imbalanced or weak cell group or module giving a reading that does not match the others; Fault in the battery control unit itself; Water ingress or contamination inside the battery pack or its connectors.

P0B59

Hybrid/EV Battery Voltage Sense G Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
B: AreaHybrid propulsion
59: FaultThe specific fault in that area

What it means

P0B59 is a generic code meaning the hybrid or EV battery control unit has detected a fault in the voltage sense circuit labelled 'G'. It set because the reading from that sensing circuit was missing, out of range, implausible, or did not agree with other battery voltage measurements. Which cell group or module circuit G refers to depends on the vehicle and battery design, so check the manufacturer's information for the specific model.

Symptoms

Hybrid or EV system warning light on the dashboard, possibly with the main warning light
Reduced power or limp-home mode
Reduced electric assist or reduced EV range
Poor fuel economy on a hybrid because the engine runs more
Car will not go into READY mode or will not charge, on some models
Other battery-related codes stored alongside it

Possible causes

Damaged, loose or corroded connector or terminal on the battery voltage sense harnesslikely
Open circuit, short or chafed wiring in the sense circuit between the battery cells or modules and the battery control unitlikely
Faulty cell monitoring board or voltage sensing circuit inside the battery packpossible
Imbalanced or weak cell group or module giving a reading that does not match the otherspossible
Fault in the battery control unit itselfrare
Water ingress or contamination inside the battery pack or its connectorsrare

How to diagnose

Read all stored and pending codes and freeze frame data, noting any other battery, isolation or communication codes.
Look up the manufacturer's definition of sense circuit G for this model and which cells or modules it covers.
Check for relevant technical service bulletins and any software updates for the battery control unit.
Carry out a visual check of accessible battery-related wiring and connectors for damage, corrosion, moisture or loose fit, following the high-voltage safety procedure.
Use a scan tool to compare individual cell or module voltages and look for one group that is out of line or reads zero or a fixed value.
Check battery state of health data and cell balance, and compare against the manufacturer's limits.
With the high-voltage system properly isolated by a trained person, test the sense circuit for continuity, resistance and shorts against the wiring diagram.
Clear the code and road test, then recheck live data to see if the fault returns and under what conditions.

How to fix

Repair or replace damaged wiring, terminals or connectors in the voltage sense circuit.
Clean and refit connectors, and deal with any source of moisture.
Replace the faulty cell monitoring board or sense module if the manufacturer allows it.
Rebalance, repair or replace the weak battery module or pack as the manufacturer specifies.
Update the battery control unit software if an outdated calibration is a known cause, or replace the unit if confirmed faulty.

Can I keep driving?

Medium severity

If the car is driving normally and there is no red warning, it can be driven carefully to a workshop, but expect reduced power and a risk of it getting worse. Stop driving and seek help if the car loses drive, shows a red high-voltage warning, or there is any smell, smoke or heat from the battery.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.