BYD ATTO 3 (e-Platform 3.0) U300316 EPB Battery Soft Undervoltage Fault

U300316 indicates a soft undervoltage condition detected by the electronic parking brake (EPB) system. The fault affects EPB electrical power management, where the controller monitors supply voltage and can detect when available voltage falls below its expected operating range. The BYD ATTO 3 uses BYD’s e-Platform 3.0 architecture, with this generation introduced from 2022 and continuing onward.

Symptoms

• EPB warning light illuminated
• Electronic parking brake warning message
• EPB may fail to apply or release
• EPB operation may become slow or intermittent
• Multiple low-voltage or communication faults may be stored
• EPB functions may become temporarily unavailable
• Warning may appear after a low-voltage event
• Caution or system messages may appear on the instrument cluster

Possible Causes

• Low 12V battery state of charge
• Weak or deteriorated 12V battery
• Low auxiliary system voltage
• Excessive voltage drop in EPB power or ground circuits
• Loose or corroded battery terminals
• Poor EPB controller power or ground connection
• Electrical load exceeding available auxiliary power
• Fault in the vehicle’s 12V charging or power-management system
• Previous battery discharge or low-voltage event
• EPB controller fault

Diagnosis

Diagnosis should begin by confirming U300316 and checking the vehicle’s 12V auxiliary system voltage under relevant operating conditions. Battery condition, terminal connections, charging performance, EPB controller power and ground circuits, and voltage drop should be evaluated against manufacturer specifications.

Other stored low-voltage or network communication faults should also be reviewed to determine whether U300316 is a primary fault or a consequence of a broader electrical supply problem. For New Zealand owners, verifying auxiliary battery condition before replacing EPB components can help avoid unnecessary repair costs.

Accurately diagnosing this fault often requires manufacturer testing procedures, wiring diagrams, connector pinouts, specifications, and system calibration information. Access to the factory service manual significantly reduces diagnostic time and helps prevent unnecessary parts replacement.

Applicable Years

2022, 2023, 2024, 2025, 2026, onwards

To order the correct OEM Service and Repair Manual for your BYD ATTO 3, submit your request using the form below and our team will provide the ordering details.