C0266
- Chassis
- Generic (SAE)
Get it looked at now
Driving may cause further damage or leave you stranded. Arrange service promptly rather than waiting.
Active Brake Booster
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
The brake control module has detected a fault in the active (electric or vacuum-controlled) brake booster. Active boosters are used by emergency brake assist and adaptive cruise control to autonomously build brake pressure.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Driving may cause further damage or leave you stranded. Arrange service promptly rather than waiting.
- Urgency
- Get it looked at now
- Will it pass emissions
- Not affected
- Check engine light
- Varies
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Active booster motor or solenoid failed | Very common | — |
| 2 | Vacuum supply weak (vacuum pump or hose fault) | Common | — |
| 3 | Wiring or connector fault | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- Active Brake Booster
- Brake Control Module
- Vacuum Pump
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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