BRAKE Master Cylinde CITROËN C4 I (LC_)

It sounds like you’ve done a lot of the right steps but still getting no foot brake pressure points strongly to a possible failing master cylinder on your Citroën C4 I (LC_). Even though the handbrake works fine, the hydraulic foot brake relies on the master cylinder to build pressure.

The master cylinder is usually located on the driver’s side firewall in the engine bay, connected to the brake fluid reservoir. To bleed it properly:
- Keep the reservoir full at all times to prevent air from getting back in.
- Bleed the brakes in the correct sequence: generally starting with the wheel farthest from the master cylinder (often the rear passenger side), then the rear driver side, front passenger side, then front driver side.
- You may need to bleed the ABS module too, as air can get trapped there, which standard bleeding won’t remove. This usually requires a diagnostic tool to cycle the ABS pump and valves to purge trapped air.

With your symptoms—no pedal pressure with the engine running but some pedal feel with the engine off—it sounds like either the master cylinder’s internal seals have failed or there’s air stuck inside the ABS system.

Advice:
- Try bench bleeding the master cylinder if removed.
- If that doesn’t help, consider master cylinder replacement.
- Use a pressure bleeder or a two-person bleeding method.
- For ABS bleeding, a professional garage with the right tools might be required.

Many Citroën C4 owners report similar issues where the ABS unit traps air, needing specialized tools to pump it out.

In summary, the master cylinder failing internally is a likely root cause, but don’t neglect the ABS bleed step, which may need professional diagnostics and bleeding.

Hope this helps get your brakes working safely again!