V70 Brake Booster Pressure Sensor Failure

That sounds familiar! I had the same problem with my Opel Insignia. Error message, hard brake pedal, and the ABS light was always on. Did you recently have any brake work done? On my Insignia, it was from an improperly bled brake system, which damaged the brake booster pressure sensor. Have you checked the brake fluid level and looked for leaks?

Thanks. I had the brake system bled about a month ago after replacing the brake pads. I didn't have any problems right after, but it started in the last week or so. Could a bad brake bleeding really cause a delayed failure of the brake booster pressure sensor? The brake fluid level looks okay, and I don't see any leaks.

Yes, it's possible that bad brake bleeding could cause a delayed failure. Air in the system or an incorrect bleeding sequence can stress the brake booster. Since you had the brakes bled recently, I suspect that's the cause. The sensor is probably damaged now. You could try re-bleeding the brakes, but I'd take it to a shop for diagnosis and repair. Driving with a faulty brake booster can be dangerous.

Thanks for the advice. I took it to a local shop. They said the brake booster pressure sensor failed, probably from air in the system after bleeding the brakes. They replaced the sensor and properly bled the brakes. The total cost was about 90€. Thanks again for your help!