What does error code C123EF0 mean?
The error C123EF0 stands for “Hydraulic Brake Booster – Limit Reached”. It typically affects Audi vehicles equipped with Bosch ABS/ESP control units (generation 9). Once stored, this fault code often cannot be cleared via standard diagnostic tools and indicates a malfunction in the hydraulic brake assist system.
Common symptoms:
- ABS or ESP warning lights on the dashboard
- Brake pedal feels hard or difficult to press
- No brake assist function
- Potential safety risk – do not drive the vehicle in this condition
- Fault persists even after attempts to clear it
Affected Audi models (examples):
- Audi A4 B9
- Audi A5 F5
- Audi A6 C7 (facelift)
- Audi A7 4K
- Audi Q5 FY
- Audi Q7 / SQ7 (2015 and newer)
(Typically vehicles from approx. 2014–2020 with Bosch ABS/ESP systems)
Repair instead of replacement
A full replacement of the control unit can be very expensive and is often unnecessary. At DIAS Automotive Engineering, we offer a professional repair service – fast, cost-effective and no re-coding required.
🔧 Our service – your advantages:
- ✅ Professional repair of the original ABS/ESP unit
- ✅ No coding or programming needed after repair
- ✅ 2-year warranty included
- ✅ Fast turnaround (usually 1–2 working days)
- ✅ Save up to 70% compared to new unit replacement
- ✅ Easy shipping from anywhere in Europe
How our repair process works:
- Fault diagnosis (C123EF0 detected)
→ You or your local workshop identify the fault using diagnostic tools - Contact & pre-registration
→ Get in touch with us and provide the fault code and part number - Shipping the control unit
→ Securely pack and ship the control unit to our German workshop – we accept units from all EU countries - Inspection & analysis
→ We examine the electronics and perform an in-depth fault analysis - Fault removal & functional testing
→ The fault is permanently removed, and the unit is fully tested on professional test benches - Return shipping & reinstallation
→ We ship the repaired unit back to you – plug & play ready, no further configuration needed
Common part numbers (examples):
- 4M0907379K
- 4M0907379T
- 4M0907379Q
- 8W0614517M
- 0265956621
(Other part numbers also supported – feel free to ask)
Pricing & turnaround:
- Price: based on part type – please request a quote
- Processing time: typically 1–2 working days
- Shipping Europe-wide via DHL, UPS or your preferred courier
Contact us now:
We repair ABS/ESP control units with error C123EF0 quickly, affordably, and professionally – including Europe-wide shipping.
📞 Phone: +49 5695 82 99 841
📧 Email: info@dias-automotive-engineering.com
📍 Workshop address:
DIAS Automotive Engineering
Tobias Huthwelker
Vor dem Südholze 5
34477 Twistetal
Germany
DIAS Automotive Engineering
Experts in control unit repairs – Repair instead of replace. Reliable. Affordable. Sustainable. Europe-wide.