self braking 996 4S 2002 :-( Faultcodes 4340 4460 4276)

[dennisvdw]

Hello everybody! My 2002 996 4S has a strange problem.....

While i left home two weeks ago, i first noticed that the brakepedal felt hard... thereafter i noticed initially that the car didnt seem to roll easily.... it felt like there was a little bit off brake power applied to the wheels.....

Entering the highway, at a speed op 70 miles/hr the wheel started to shiver , initially a little bit, but quickly increasing in force. I thought it was a flat tire, so i stopped..... When speed decreased i noticed that the car was braking by itself. After the car came to a full stop, and i checked the tires ( no flat tires) i tried to drive away but i couldnd, the wheels were locked..... I had to call for a tow a way truck...... I saw three warnings on the dash, amber: psm failure, drive to workshop, amber: ABS failure and red: WARNING brake distribution......

the strange thing however: after the car was delivered to the dealer it seemed to be ok..... No more warnings and the wheels were free again.... I noticed that brakefluid was forced out of the reservoir a little bit.....

The dealer is looking into the problem now for two weeks already and they still have no glue what the problem is.... It comes back after a few minutes of driving the car....

Faultcodes:

4340

4460

4276

Does anybody have an idea? I hope somebody recognice the problem........

Thanx for reading this post anyway!

Dennis

[Loren]

Fault code 4276 -- Valves voltage supply

Possible cause of fault

- Fuse E9 faulty

- Short circuit or open circuit in the B+/ground supply to the control unit

- Hydraulic power unit faulty

Fault code 4340 -- Stop light switch

Possible cause of fault

- Fuse E9 faulty

- Short circuit or open circuit in the B+/ground supply to the control unit

- Hydraulic power unit faulty

Fault code 4460 -- Pressure sensor

Possible cause of fault

- Short circuit to ground/8+ or open circuit

- Plug connection on stop light switch faulty

- Incorrect adjustment of the stop light switch

- Wiring/plug connection between pressure sensor and control module faulty

- Pressure sensor faulty

I would start with fuse E9 - then reset the codes and see which come back.

[dennisvdw]

The problem was finally solved after replacement of the master brake cylinder, an 150 dollar part..... Replacement of the abs sensors didnt solve the problem, neither did replacing the brake control unit....