On Board Diagnostic (OBD), Specific Functions

On Board Diagnostic (OBD), specific functions
The OBD function of the ABS/EDL system can recognize malfunctions and store a total of 14 different Diagnostic Trouble Codes (DTCs) (19 for vehicles with ASR traction control).

Self-test
Each time the ignition is switched on, the system conducts a self-test. The yellow ABS warning light -K47- comes on to indicate that this self-test is being conducted. On vehicles with ASR the traction control indicator light -K86- will also light up. The ABS warning light goes out after about 2 seconds. The self-test continues after the vehicle starts moving, as certain malfunctions cannot be recognized until the vehicle is moving.
The self-test may be recognized by the switching of relays, the start-up noise of the ABS return flow pump (at the ABS hydraulic unit), and by a slight vibration at the brake pedal. These system-related effects are part of the self-test program, and this should be explained to customers in the event of complaints.

Notes:
- If a malfunction is recognized by OBD, the system concerned is switched off automatically for the duration of the current driving cycle. This is indicated by the relevant warning light in the instrument cluster. For further details, Refer to: "Warning lamp functions". Refer to Warning lamp functions.
- The note above does not apply to DTC 00526 "Brake Light Switch-F" or DTC 00668 "Battery Positive Voltage (B+) Term.30", Refer to: DTC table. About Trouble Codes The warning light does not come on when one of these DTCs is stored. These malfunctions only affect EDL function.

WARNING: If VAG 1557 is connected and a communication fink has been established to the ABS control module -J104-, bear in mind that the function of the brake system is limited, and there is a risk of accident if the vehicle is driven. The brake pressure at the rear wheels is no longer controlled by the Electronic Brake Distribution (EBD) function. This can result in excessive braking at the rear, and the vehicle may skid unexpectedly under braking.