Test drive

Some DTCs are only recognized by the On Board Diagnostic while the vehicle is moving. You can check the system by carrying out a test drive. During the test drive, drive at 60 km/h for 30 seconds. Make sure the traffic is clear and then brake hard enough to activate the ABS. You will feel a pulsing in the brake pedal indicating the system is active.

CAUTION: If the OBD has recognized a malfunction then the brake system is only partially functional. Because the brake pressure at the rear wheels is no longer regulated via Electronic Brake Distribution (EBD), the rear wheels can lock even during light braking. This can cause the rear end of the vehicle to break loose and therefore lead to an accident.

If the customer has reported a malfunction or problem, troubleshoot according to the customer complaint

CAUTION: If test and measuring instruments are required during a test drive, these must always be secured to the rear seat and operated by a second person from this position. If test equipment were operated from the front passenger seat, the person sitting there could be injured if the front passenger airbag were triggered in the event of an accident.

First switch the ignition on, and note whether the indicator lights light up. The table in INDICATOR LIGHT FUNCTIONS, OVERVIEW will provide a starting point.
Observe test conditions. See TEST CONDITIONS .
Connect the VAG1551 scan tool and select the address word 03 "Brake Electronics". See VAG1551 SCAN TOOL (ST), CONNECTING AND ENTERING ADDRESS WORD .
Check the control module version (see CONTROL MODULE VERSIONS (SCAN TOOL FUNCTION 01), CHECKING ) and press --> button.
Check DTC memory. See DIAGNOSTIC TROUBLE CODE (DTC) MEMORY (SCAN TOOL FUNCTION 02), CHECKING . If a DTC is stored: make a note of the DTC and erase the DTC memory. See ERASE DTC MEMORY .
End data transfer using the "End Output" function. See END OUTPUT .
Repair the malfunction with the help of the DTC table. See DTC TABLE; DTCS 00000 TO 00526 . Select again the address word 03 "Brake Electronics." Check and erase DTC memory.
End data transfer using the "End Output" function. Disconnect VAG1551 scan tool.
Make sure all connections are connected properly. Carry out a test drive. See TEST DRIVE . The indicator lights must not light up during the drive. If the indicator lights light up during the test drive, repeat the troubleshooting procedure.
NOTE: If the control module connector is disconnected during the drive, an unfounded DTC may be stored in the memory of another control module. The mechanical and hydraulic brake system functions will continue to work. However, with a system failure the brake pressure regulator is deactivated meaning there is an increased chance of an accident while driving.

CAUTION: On vehicles equipped with Audi Telematics by OnStar(R), switch-off the emergency (back-up) battery for the Telematic/Telephone Control Module prior to disconnecting the vehicle battery. See EXAMPLE: SWITCH OFF EMERGENCY (BACK-UP) BATTERY . Switch-on the emergency (back-up) battery after reconnecting the vehicle battery. See EXAMPLE: SWITCH ON EMERGENCY (BACK-UP) BATTERY .

Switch ignition off before carrying out any work on vehicle. Determine anti-theft radio code for radios with anti-theft radio code and disconnect battery Ground (GND) strap.
Remember that there are certain procedures that must be carried out after connecting the battery, such as: setting the clock. Read procedures under RECONNECTING BATTERY, PROCEDURES .
Only replace a malfunctioning component if you are certain that all electrical lines to this components are functioning properly. The lines must work properly and be capable of carrying all signals without any problems. Check the lines for the following:
- Corrosion or loose connections in the connectors or Ground (GND) straps. If there are bent, broken or corroded terminals on the connectors, replace the terminals using VAS1978 wiring harness repair kit.
- Open circuit in wiring
- Short circuit to B+ or Ground (GND)
NOTE: The instruction manual for the VAS1978 wiring harness repair kit generally forbids the repair of any lines in the ESP or related systems. This rule only pertains to the shielded lines in these systems.
When replacing a control module, make sure you install the correct control module. First check the control module version. The version is displayed after the communication is established between the VAG1551 scan tool and the control module, in the VAG1551 display, or after selecting the "Check Control Module Versions" function 01. See CONTROL MODULE VERSIONS (SCAN TOOL FUNCTION 01), CHECKING . You can also determine which equipment is installed in the vehicle using the letter combinations on the vehicle data label.
- 1AC: Anti-lock Brake System (ABS)
- 1AH: Anti-lock Brake System with Electronic Differential Lock (ABS/EDL)
- 1AJ: Anti-lock Brake System with Electronic Differential Lock and traction control system (ABS/EDL/ASR)
- 1AT: Anti-lock Brake System with Electronic Differential Lock and traction control system (ABS/EDL/ASR) and Electronic Stabilization Program (ESP)
- All work on the ABS Hydraulic Unit must be carried out with the utmost cleanliness. Thoroughly clean the hydraulic line connections and the area around them. Do not use any aggressive cleaning agents, such as brake fluid, gasoline, thinning agents, or any fluids containing mineral oil, such as oils and greases. Do not disconnect hydraulic lines until you have cleaned the connections.
- Note the appropriate precautions regarding handling of brake fluid.
  See BLEEDING BRAKE SYSTEM .
- Place removed parts on clean surface and cover them. Only use lint-free cloths.
- Only use genuine packaged parts, and only remove replacement parts from their packaging immediately prior to installation.
- Bleed brake system if connections in system have been opened.
  See BLEEDING BRAKE SYSTEM .
- Welding using electrical welding equipment can affect the ESP system.