C123EF0
ABS / stability-control fault code, listed for 1 vehicle line from Audi. What it means on each one, with sources, and when the module is the cause.
What C123EF0 means
Hydraulic Brake Booster Limit Value Reached
On: 2016-2020 Audi A4 / A4 allroad / A5 (B9)
Is it the ABS module?
Check the cheap things first: battery voltage and the main fuses for the ABS pump and module, the ground straps, the module connector (corrosion, a pushed-back pin) and, for wheel-speed codes, the sensor and its wiring at each wheel. If those are good and the code returns as soon as it is cleared — or the scan tool cannot talk to the ABS module at all — the module itself is the likely cause, and that is what we repair.
Vehicles that set C123EF0
C123EF0 by vehicle
What does C123EF0 mean on a Audi A4 / A4 allroad / A5 (B9)?
The source we cite for the 2016-2020 Audi A4 / A4 allroad / A5 (B9) lists it as: Hydraulic Brake Booster Limit Value Reached. That vehicle uses Bosch Bosch 9.0 ABS/ESP (a rebuilder 'Bosch 9.0 ABS Module for 2014-2020 Audi'). We repair it as part of the Bosch ABS / ESP 9 family, from $499.
Still not sure?
Send us C123EF0, a photo of the module label and your VIN — we tell you whether the module is the likely cause and what it costs, before you pull anything. Asking costs nothing.
C123EF0 keeps coming back after the checks? Fix the module — from $499.
Look up your part number and order online — we email you a prepaid label to our lab. Or send us a photo of the label and your VIN first, and we'll tell you what you have and what it costs.
Back with your VIN and coding · can’t be repaired? repair price back, minus shipping · 1-year warranty · rush 2–3 days +$100
Call (817) 505-4201 · 📱 Text us a photo of the module label · Ask first — send a label photo · Email repairs@absmodulelab.com