Poor connection, corrosion or loose terminals in the voltage sense wiring or connector at the battery pack or control unit; Damaged, chafed or open-circuit or short-circuit sense wiring; Faulty cell voltage monitoring circuit or sensing board within the battery pack; Imbalanced or degraded battery cells or modules causing a genuine voltage deviation; Blown sense fuse or damaged busbar or sense lead connection at the pack; Faulty battery control unit or an outdated calibration where the manufacturer has published a fix.

P0B55

Hybrid/EV Battery Voltage Sense F Circuit Range/Performance.

Generic
Powertrain
Generic code
Medium severity

How this code is built

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

What it means

P0B55 is a generic powertrain code meaning the hybrid or EV battery control unit has found the voltage sense 'F' circuit reading out of its expected range, or not agreeing with other voltage measurements. The control unit compares this reading with the other sense circuits and the total pack voltage. The exact location of circuit 'F' depends on the manufacturer and the pack design, so check the model-specific data.

Symptoms

Hybrid or EV system warning light on the dashboard
Malfunction indicator lamp lit
Reduced power or limp-home mode
Hybrid system not engaging, so the engine runs more or the car relies on the engine only
Reduced electric range or poor battery state-of-charge readings
Car will not go into Ready mode or will not charge

Possible causes

Poor connection, corrosion or loose terminals in the voltage sense wiring or connector at the battery pack or control unitlikely
Damaged, chafed or open-circuit or short-circuit sense wiringlikely
Faulty cell voltage monitoring circuit or sensing board within the battery packpossible
Imbalanced or degraded battery cells or modules causing a genuine voltage deviationpossible
Blown sense fuse or damaged busbar or sense lead connection at the packpossible
Faulty battery control unit or an outdated calibration where the manufacturer has published a fixrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting any other battery voltage, cell balance or insulation codes.
Check for manufacturer service bulletins and the definition of sense circuit F for this model and pack.
Carry out a visual inspection of the sense wiring, connectors and pack seals for damage, corrosion, water ingress or loose fit, following high-voltage safety procedures.
Use live data to compare individual cell or block voltages with the total pack voltage and look for an outlier or a reading stuck at zero or maximum.
Check the state of charge, cell balance and the temperature spread across the pack.
Once the high-voltage system is isolated by a qualified person, test the sense circuit wiring for continuity, resistance and shorts against the wiring diagram.
Check the relevant fuses and the sense lead and busbar connections at the pack.
Clear the code and road test, then recheck whether it returns and whether the readings stay consistent.

How to fix

Clean, repair or replace faulty connectors and terminals in the sense circuit.
Repair or replace damaged sense wiring.
Replace the faulty sensing board, module or pack section as the manufacturer's procedure allows.
Rebalance or replace weak cells or modules where testing shows a genuine voltage deviation.
Update or reflash the battery control unit software only if the manufacturer lists it as a fix, or replace the unit if it is proven faulty.

Can I keep driving?

Medium severity

The car may still be driveable, often in a reduced power mode, but get it checked soon because the fault can worsen and affect the hybrid system. Stop driving and seek help if the car loses power suddenly, shows a high-voltage or safety warning, or there is any smell, heat or damage around the battery.

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