BYD ATTO 3 (e-Platform 3.0) C1B9D22 EPS Power Supply Voltage Too High

C1B9D22 indicates that the electronic power steering (EPS) controller has detected a power supply voltage above its expected operating range. The fault affects the electric steering assist system, which requires a controlled electrical supply to operate the steering motor and associated control electronics correctly. The BYD ATTO 3 uses BYD’s e-Platform 3.0 architecture, with this generation introduced from 2022 and continuing onward.

Symptoms

• EPS or steering warning light illuminated
• Steering may become heavier than normal
• Reduced or lost electric power steering assistance
• Steering system warning message displayed
• Intermittent steering assistance
• EPS-related diagnostic trouble codes stored
• Other voltage or communication warnings may appear
• Fault may occur following a 12V electrical system event

Possible Causes

• Excessive 12V auxiliary system voltage
• Fault in the vehicle’s 12V charging or power-management system
• Voltage regulation fault
• Damaged EPS power supply wiring
• Poor or unstable EPS controller power connection
• Loose, damaged, or corroded electrical terminals
• Electrical voltage surge
• Faulty EPS controller voltage-monitoring circuit
• Incorrect electrical system repair or connection
• Internal EPS controller fault

Diagnosis

Diagnosis should begin by confirming C1B9D22 and measuring the 12V auxiliary system voltage under the operating conditions specified by the manufacturer. Battery condition, charging or power-management operation, EPS power and ground circuits, wiring, connectors, and voltage stability should then be assessed against factory specifications. Other voltage-related diagnostic codes should be reviewed to determine whether the EPS overvoltage condition originates from the vehicle’s wider electrical supply system or within the EPS circuit itself. For New Zealand owners, verifying the source of the excessive voltage before replacing EPS 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.