An Audi A4 B9 displaying C123EF0 in the ABS or brake electronics can bring on ABS and traction-control warnings, along with a brake-system or hydraulic brake-booster pressure message. The fault is associated with Bosch ESP9-family ABS pump/module systems. Because braking and stability systems are safety-critical, a qualified workshop should diagnose the vehicle before parts are removed or ordered.
What C123EF0 can look like on an Audi A4
- ABS warning lamp illuminated
- Traction-control or stability-control warning
- Brake-system warning such as “Brake system fault – stop carefully”
- Hydraulic brake-booster pressure fault recorded during diagnostics
Why a proper diagnosis matters
C123EF0 should be read with the complete ABS scan report, vehicle details and the part number on the pump/module label. Wiring, power supply, connectors and the wider brake system must be checked before the unit is condemned. The fault can affect ABS and stability-control operation, so do not ignore warning messages or rely on normal driving behaviour as proof that the system is safe.
Audi A4 B9 applications
The Essex Recons repair service covers listed A4 applications from 2015–2019 using the Bosch ESP9-family pump/module. One commonly listed family is 8W0907379G / Bosch 0265956241, but specifications vary. Always confirm the exact number from the original unit or a diagnostic scan.
Repairing the original ABS pump/module
Where the diagnosis supports an internal unit fault, repairing the original module can avoid the uncertainty of fitting an unknown used replacement. Essex Recons tests, repairs and returns the customer’s original ABS pump/module.
View the Audi A4 C123EF0 ABS pump repair service
Before sending a unit
Please provide the vehicle registration, the full fault code and the ABS pump part number. Follow the correct manufacturer procedure for removal and refitting, and ensure any brake-system work is completed and checked by a competent technician.
FAQ
Does C123EF0 always mean the ABS pump has failed?
No. It is a diagnostic starting point. The complete brake-electronics report, wiring and power supply should be checked first.
Can I fit a used A4 ABS module instead?
Used units may have unknown history and can introduce coding or compatibility issues. Confirm the correct repair route for your vehicle and module number first.
