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fiRed light spells danger! Audi A4 C123EF0 Brake Boost Fault Code
Hydraulic brake boost error – What does it mean?
C123EF0 is a fault code that we have seen become increasingly common in the Audi A4 8W / B9 that entered production in 2015. The fault code means that there is a problem with the amount of brake boost pressure available. The fault code will trigger a red warning light with an exclamation mark (similar to the handbrake warning light) to remain illuminated.
What causes the C123EF0 fault code?
The fault originates as an issue with the brake booster vacuum sensor. Once this fault is logged, the ABS uses an accumulated pressure source to operate/increase the level of braking assistance. Once the accumulated pressure is released (after you've used the brakes a few times), the system is unable to restore the pressure. The fault is often down to the Bosch 9 ABS unit fitted to these models.
Important note: Cars with this fault can suffer from a lack of pedal pressure.
Working on an A4? Here is what to look out for...
The Bosch 9.0 builds on the success of its predecessor, the Bosch 8. The software used has a modular structure, and a variety of versions are available depending on the required application. Boschclaims that its 9th generation is 30% lighter, meaning an ABS unit now weighs just 1.1kg.
Despite the lower weight, there is no sacrifice in functional terms. Investigations by our in-house R&D team resulted in a fully reverse-engineered part that we're able to offer a full remanufacturing service for. Like the rest of our repairs, it's a plug-and-play solution, with no need for additional programming, all at a fraction of the cost of a new replacement.
So, the next time you're working on an A4, and you come face to face with the C123EF0 fault code. Make sure you reach out to our customer service team, and they'll be sure to help.