Electronic brake force distribution

The brake system is split diagonally into two hydraulic circuits: one supplying the left front and right rear brakes and one supplying the right front and left rear brakes.

The ABS control module (w/EDL) -J104- is programmed with specially designed software for electronic brake force distribution, which takes over the function of the mechanical or hydraulic brake pressure limiter.

In cases where a failure of the ABS has occurred, but the electronic brake force distribution function can still be maintained by a back-up feature, the signal sent to the instrument cluster is pulsed. The instrument cluster distinguishes between three conditions: no signal present, pulsed signal, and continuous signal present. The ABS/EDL warning light and the brake system warning symbol come on in accordance with the signal received.

Fig 1: ABS/EDL Warning Light And Brake System Warning Symbols

Courtesy of AUDI OF AMERICA, INC.

1. Terminal 15
2. Signal for activation of ABS/EDL warning light and brake system warning symbol
3. Supply voltage for ABS/EDL warning light
4. Supply voltage for brake system warning symbol

Fig 2: ABS/EDL Warning Light And Brake System Warning Symbols

Courtesy of AUDI OF AMERICA, INC.

1. During phase "A" (after ignition is switched on) the ABS/EDL warning light is activated for two seconds during the self-test by means of signal "2", and comes on. During this phase an internal function in the instrument cluster suppresses the activation of the brake system warning symbol.
2. During phase "B", signal "2" is not present. The ABS/EDL warning light and brake system warning symbol do not come on.
3. In phase "C", On Board Diagnostic (OBD) has detected a malfunction which does not cause the electronic brake force distribution function to be switched off. Signal "2" is pulsed. Only the ABS/EDL warning light comes on.
4. In phase "D", On Board Diagnostic (OBD) has detected a malfunction which causes the electronic brake force distribution function to be switched off. Signal "2" is present continuously. Both the ABS/EDL warning light and brake system warning symbol come on.

If the brake system warning symbol comes on, this indicates that the electronic brake force distribution function is out of action. If the vehicle has to be driven in this condition, extra caution is required. See  TROUBLESHOOTING ABS AND ESP, SAFETY PRECAUTIONS AND GENERAL NOTES   , Road testing. 

For further information on the activation of the warning lights in connection with the electronic brake force distribution function. See WARNING LIGHT FUNCTIONS TABLE  .