C05A9ABS Pump Motor Supply Voltage Circuit A/B Correlation
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- With two feeds for the pump motor, the module can compare them: both come from the same vehicle supply and should read almost alike. C05A9 is set when the two drift apart beyond the allowed margin, even though each may still lie in its own window. A Hitachi patent for electric brakes uses this idea: the control unit compares the voltages of several branch supply lines and, if the largest difference exceeds a limit, concludes that a main line is broken and switches in a backup path. Hyundai Mobis gives each winding of a dual brake motor its own power module and supply input, and Ipgate runs its brake-by-wire electronics on two redundant supplies. No maker documents C05A9 publicly. Likely causes are a high-resistance connection in one feed or a measuring error in the module.
- What you may notice
- ABS/ESC or brake system warning lamp on
- Pump operation or brake redundancy restricted
- Likely causes
- LikelyCorroded terminal, fuse or connector in only one of the two feeds
- PossibleVoltage measurement channel in the brake module drifting
- RarePoor ground affecting only one supply path
- Repair
- Medium · Usually a job for a workshop.Typical cost: €30 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.