Complete guide to Sensotronic Brake Control diagnostic trouble codes
Diagnostic Reference
The SBC (Sensotronic Brake Control) system by Bosch monitors braking operations, pump RPM, and fluid service intervals. When faults are detected or thresholds exceeded, it logs diagnostic trouble codes and may display "Service brake! Visit workshop!" on your dashboard.
| Code | Description | Severity |
|---|---|---|
| C249F | Lifetime counter exceeded — The SBC pump has reached its programmed service life (~300,000 brake actuations). Triggers "Service brake! Visit workshop!" message. | Medium |
| C2498 | High-pressure reserve depleted / Lifetime counter service message — Often appears with C249F. Indicates pressure system needs inspection. | Medium |
| C2131 | Soft accumulator (preload pressure below spec) — The hydraulic accumulator has failed or is failing. Pump rebuild or replacement required. | High |
| C217B | Valve relay power supply fault — Check electrical connections to the SBC unit. May be wiring issue or internal relay failure. | Medium |
| C223C | Hydraulic fault A7/3y6 — Front-left inlet control valve fault. Internal hydraulic component failure. | High |
| C22BD | Pressure increase fault (front left / VL) — Unable to build pressure to front left brake circuit. | High |
| C223D | Pressure increase fault (front right / VR) — Unable to build pressure to front right brake circuit. | High |
| C233D | Pressure increase fault (rear left / HL) — Unable to build pressure to rear left brake circuit. | High |
| C23BD | Pressure increase fault (rear right / HR) — Unable to build pressure to rear right brake circuit. | High |
| C226F | Internal control unit A7/3n1 error — Internal electronic fault in the SBC control module. | High |
| C22EF | Internal control unit error — Electronic control unit internal fault. | High |
| C254F | Internal control unit A7/3n1 error — Variant of internal electronic fault. | High |
| C258F | Internal control unit error — Electronic control unit internal fault. | High |
| C235A | Wear detection / pressure regulation fault — Pressure sensor or regulation system fault. | Medium |
| C235B | Wear detection fault — System wear monitoring has detected an issue. | Medium |
| C235C | Motor relay fault — The relay controlling the SBC pump motor has failed. | High |
| C235D | Solenoid valve fault — One or more internal solenoid valves have failed. | High |
| C235E | Pump motor fault — The SBC hydraulic pump motor has failed or is failing. | High |
| C2359 | Internal fault — General internal SBC unit fault requiring inspection. | High |
| C25D4 | Pressure supply fault — System unable to maintain required pressure levels. | High |
| C26BB | Hydraulic error — preload below specification — Accumulator precharge pressure too low. | High |
| C26BE | Hydraulic pressure error — General hydraulic system pressure fault. | High |
| C26F5 | Pressure supply / hydraulic error — Hydraulic pump or pressure supply system fault. | High |
Understanding Warnings
"Service Brake Visit Workshop" in grey/white indicates the system is in backup mode. Reduced braking to front wheels only. You can drive carefully but arrange repair urgently.
A RED brake warning indicates a serious fault. STOP IMMEDIATELY. Do not attempt to drive. Pull over safely and arrange vehicle recovery.
Next Steps
If you've scanned your Mercedes and found any of these fault codes, contact us with:
We'll advise on the best repair option for your situation: