Audi A5 ABS ECU C123EF0 Fault Repair
Pelican Diagnostics UK provides a specialist Audi A5 ABS ECU C123EF0 Fault Repair for Audi A5 B9 vehicles fitted with the Bosch ESP 9 ABS system.
This is an in-person repair service only. The complete vehicle must be brought to our workshop in Sleaford. The repair normally takes approximately 15 minutes and can be completed while you wait.
The brake-booster vacuum sensor must be replaced before attending your appointment. Any vacuum leaks or related brake-assistance faults must also be repaired before we carry out the ABS ECU reset.
- Service: Audi A5 C123EF0 Repair
- Price: £175
- Repair Time: Approximately 15 minutes
- Service Type: In-person vehicle repair only
- Location: Sleaford, Lincolnshire
- Appointment: Required
- Important: Vacuum sensor must be replaced before booking
- Postal Repair: Not available
How to Book
- Have the vehicle professionally diagnosed and confirm that fault code C123EF0 is stored in the ABS control unit.
- Replace the brake-booster vacuum sensor.
- Repair any vacuum leaks or related brake-assistance faults.
- Contact Pelican Diagnostics to arrange an appointment.
- Bring the complete Audi A5 to our Sleaford workshop at the agreed time.
- We will carry out the ABS ECU repair while you wait. The procedure normally takes around 15 minutes.
Workshop address:
Pelican Diagnostics UK
Padley Farm
Drove Lane
Sleaford
Lincolnshire
NG34 8JQ
Please do not remove or post the ABS module for this service. The complete vehicle must be present.
What Does Audi Fault Code C123EF0 Mean?
Audi fault code C123EF0 indicates that the hydraulic brake-booster or brake-servo limit has been reached.
The fault is commonly linked to a defective brake-booster vacuum sensor, insufficient vacuum pressure, damaged vacuum pipework or another fault within the brake-assistance system.
After the fault has occurred repeatedly, the Bosch ESP 9 ABS control unit can enter a locked state. In this condition, C123EF0 may remain stored permanently and cannot usually be cleared using standard diagnostic equipment.
Once the underlying vacuum-system fault has been corrected, we can professionally reset the locked ABS ECU and restore normal operation.
Fault Codes Covered
- C123EF0 – Hydraulic Brake Booster Limit Value Reached
- C123EF0 – Hydraulic Brake Servo Limit Reached
This service is specifically intended for vehicles with the C123EF0 ABS lockout condition. The vehicle should be professionally diagnosed before booking.
Vacuum Sensor Must Be Replaced First
The brake-booster vacuum sensor must be replaced before the vehicle is brought to us.
The vacuum sensor or an associated vacuum-system problem is normally the original cause of the C123EF0 fault. If the cause is not repaired before the ABS ECU is reset, the same fault may return.
Before booking, your garage or technician should:
- Replace the brake-booster vacuum sensor
- Inspect the vacuum pipes for leaks, splits or damage
- Check the brake booster and vacuum supply
- Repair any related vacuum-system faults
- Confirm that C123EF0 remains stored and cannot be cleared normally
Supported Audi Models
- Audi A5 B9 Coupe
- Audi A5 B9 Sportback
- Audi A5 B9 Cabriolet
- Audi S5 B9
- Selected Audi A5 models fitted with the Bosch ESP 9 ABS system
Please send us the vehicle registration, VIN and diagnostic fault report before booking if you are unsure whether your Audi A5 is supported.
Supported ABS ECU Part Numbers
- 8W0907379AA
- 8W0907379AB
- 8W0907379AC
- 8W0907379AD
- 8W0907379AF
- 8W0907379AG
- 8W0907379AH
- 8W0907379AJ
- 8W0907379E
- 8W0907379F
- 8W0907379G
- 8W0907379J
- 8W0907379K
- 8W0907379M
- 8W0907379Q
These are common examples. Additional Bosch ESP 9 ABS ECU part numbers may also be supported.
Common Symptoms
- ABS warning light illuminated
- ESC or traction-control warning light
- Brake-system warning displayed
- C123EF0 cannot be cleared
- Hydraulic brake-booster limit reached
- Fault remains after replacing the vacuum sensor
- Reduced or inconsistent brake assistance
What Is Included?
- In-person Audi A5 C123EF0 ABS ECU repair
- Specialist correction of the locked ABS fault condition
- Diagnostic clearing of the relevant ABS fault
- Approximately 15-minute while-you-wait service
- Repair carried out with the ABS unit fitted to the vehicle
This service does not include replacement of the vacuum sensor, diagnosis of vacuum leaks, mechanical brake repairs, ABS hydraulic-block replacement or removal and refitting of the ABS unit.
Important Information
- This is an in-person service only.
- The complete Audi A5 must be brought to Sleaford.
- An appointment is required before travelling.
- The vacuum sensor must be replaced before attending.
- All underlying vacuum-system faults must be repaired first.
- Do not remove or post the ABS ECU.
- The £175 price applies to the C123EF0 repair described on this page.
- The repair normally takes approximately 15 minutes.
Why Choose Pelican Diagnostics?
- Specialists in Audi Bosch ESP 9 ABS systems
- Fast while-you-wait repair
- Approximately 15-minute turnaround
- No ABS module removal required
- Professional diagnostic and programming equipment
- Convenient Sleaford workshop location
- Trade and retail customers welcome
Contact Pelican Diagnostics UK
Contact us before travelling to confirm compatibility and arrange your Audi A5 C123EF0 repair appointment.
- 📧 Email Pelican Diagnostics
- 📱 Send us a WhatsApp Message
- 📍 Pelican Diagnostics UK
Padley Farm
Drove Lane
Sleaford
Lincolnshire
NG34 8JQ
Frequently Asked Questions – Audi A5 C123EF0 Repair
What does Audi A5 fault code C123EF0 mean?
C123EF0 means that the hydraulic brake-booster or brake-servo limit has been reached. After repeated vacuum-system faults, the ABS control unit may enter a locked state.
Is this an in-person repair?
Yes. This service is only available with the complete vehicle present at our workshop in Sleaford.
Can I post the ABS module to you?
No. Do not remove or post the ABS module. The complete Audi A5 must be brought to us.
Do I need an appointment?
Yes. You must arrange an appointment before travelling to our workshop.
How long does the repair take?
The repair normally takes approximately 15 minutes and can be completed while you wait.
How much does the Audi A5 ABS Module Repair cost?
The service costs £175.
Must I replace the vacuum sensor first?
Yes. The brake-booster vacuum sensor must be replaced before your appointment.
Why must the vacuum sensor be replaced before the repair?
The vacuum sensor or another vacuum-system fault normally causes C123EF0. If the underlying cause is not corrected, the ABS ECU may become locked again.
Can you replace the vacuum sensor?
No. The vacuum sensor must be replaced before the vehicle is brought to us for this service.
Can standard diagnostic equipment clear C123EF0?
Once the Bosch ESP 9 ABS ECU has entered a locked state, the fault may not clear using normal diagnostic equipment.
Which Audi A5 models are supported?
This service covers compatible Audi A5 B9 Coupe, Sportback and Cabriolet models fitted with the Bosch ESP 9 ABS system.
How can I confirm compatibility?
Send us the vehicle registration, VIN, ABS part number and diagnostic report by email or WhatsApp before booking.
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