BMW E46 320cd 150hp (2004) ABS (DSC) brake pressure sensor 1 fault

Hello guys,

The car has two pressure sensors threaded into the master brake cylinder. #2 has 0 bar (0psi) and #1 has 7-10bar (100-150psi) oscillating regardless if the engine is running or not, even 5 bar lowest, when I knocked on it with the screwdriver.

My main question as I don't have enough knowledge on the ABS systems = Is it somehow possible for master brake cylinder to hold its pressure when the brake pedal is depressurised and even with the key off engine off?

I cannot get to the sensor to unbolt it to see if the pressure value falls as it lives in hell.

The #2 sensor didn't even changed it's values when i knocked on it.

Thank you Very much for your response guys.

Hey ione! The short answer is yes, it's possible for the master cylinder to maintain pressure on the hydraulic system with the engine off and no pressure on the brake pedal. The most common way I've seen this to happen is if the master cylinder or brake booster gets replaced, and the push rod clearance is incorrect.

That said, if there truly was 150 PSI of rest pressure in the brake hydraulic system, you'd have other problems besides a trouble code and a dash light. Like, the brakes would be dragging. :lol: If you truly want to eliminate this possibility, you can just crack loose both brake lines at the master cylinder. Any residual pressure should bleed off. If the 150 PSI reading remains, you know it's a true electrical issue.

Hey Tyler, thank you for your response, it is amazing, that I can talk to someone.

There are no driveability problems, just the stabilisation system is not working.

One another test came to my thought, that if there was really 150psi pressure in the rear brake system (#1) I wouldn't be able to turn rear wheels if i lifted up the rear of the car, is that correct?

Yes that's a good test with that lines loosened up to depressurise system I can access that.
Thank you again that answered my question, you've been very helpful.