P0B27: Hybrid Battery B Voltage

What it means

The control module detects a fault related to hybrid battery B voltage. The code alone does not identify whether the cause is the battery or its voltage measurement.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

Hybrid battery B is a high-voltage battery section or assembly, and the battery control system uses a measurement circuit to monitor its voltage. P0B27 identifies a fault associated with battery B voltage, but its title does not specify whether the voltage is high, low, or unstable, so the stored data and live readings are needed to narrow the condition.

Common causes

Most likely first.

1. Battery voltage measurement circuit fault
2. Battery B voltage outside expected range
3. Loose or corroded electrical connection

Symptoms

• EV/hybrid system warning light on
• Reduced power output or limp mode
• Charging may fail or be slowed
• Reduced electric range

How to diagnose it

1. Read freeze-frame data and battery live readings to establish how battery B voltage differs from the expected range and from other sections.
2. Check for companion codes that identify a low, high, unstable, or charging-related condition affecting battery B.
3. With the high-voltage system made safe by the manufacturer's procedure, inspect battery B's accessible connectors, terminals, and wiring for corrosion, looseness, or damage.
4. Monitor battery B voltage during the operating condition recorded in freeze-frame data and check for dropouts or a persistent mismatch.
5. Test battery B's voltage measurement circuit and the battery section using the manufacturer's diagnostic procedure.

Common fixes

• Clean and secure a loose or corroded battery B connection.
• Repair damaged wiring or terminals in the battery B voltage measurement circuit.
• Service or replace battery B if testing confirms its voltage is outside the expected range.

Can I keep driving?

Keep trips short and avoid hard acceleration until the hybrid system has been checked, since reduced power or charging problems can worsen unexpectedly. If the vehicle enters limp mode or displays a severe battery warning, stop safely and arrange service.