Safety Precautions and General Troubleshooting Information

Safety Precautions And General Troubleshooting Information

CAUTION: ABS/EDL and ABS/EDL/ASR are safety systems, knowledge of the systems is essential for performing repair work.





"Low-line" version
- ABS warning light -K47- (right arrow).
- Warning light for brake system -K118- (center arrow, red brake warning symbol).
- Traction control indicator light -K86- (left arrow).
- If the brake system is not fully functional, but the ABS warning light -K47- and the red brake warning symbol do not light up, the malfunction must be identified by troubleshooting the conventional braking system (mechanical or hydraulic components).
Refer to Steering and Suspension.





"High-line" version with driver information display
- Red brake warning symbol lights up in the driver information display (arrow).
Refer to: Warning lamp functions.
- If the brake system is not fully functional, but the ABS warning light -K47- and the red brake warning symbol do not light up, the malfunction must be identified by troubleshooting the conventional braking system (mechanical or hydraulic components).
Refer to Steering and Suspension.
Further details are described in Warning lamp functions.

General repair information

CAUTION:
- Before disconnecting the battery, determine the correct coding for the anti-theft radio.
- Switch the ignition off and disconnect the battery Ground (GND) strap before removing and installing components.

If a component is indicated as being faulty, only replace it if you are sure that the electrical wiring for that component is in proper condition. The wiring must be able to transmit the necessary signals without interference or resistance.
- Check wiring for:
- Corrosion and loose terminals (intermittent open circuit) in harness connectors and Ground (GND) connections. If any of the connector terminals are bent, broken or corroded, use the VAS1978 wiring repair kit to install new terminals.
- Open circuits
- Short circuits to Ground (GND) or to 13+
Refer to Diagrams/Diagnostic Aids.

Note: The instructions supplied with the VAS 7978 wiring repair kit do not permit repairs to the shielded wiring of the ABS/EDL and related systems.

If the control module has to be replaced, make sure that the correct version is installed, i.e. first check the control module identification. The identification appears on the scan tool display after the data link is established, and can also be called up using "Check Control Module Version". Check Control Module Versions (Scan Tool Function 01)
You can also identify which equipment is installed in the vehicle from a combination of letters on the vehicle data label, which is located in the spare wheel well.
- 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)

CAUTION:
- Absolute cleanliness is required when working on the ABS hydraulic unit.
- Carefully clean the hydraulic connections and adjacent parts.
- Do not use aggressive cleaning agents such as brake cleaner, gasoline, thinners or any products such as oils, greases, etc., that contain mineral oil.
- Do not disconnect hydraulic lines until you have cleaned the connections.
- The bolts on the ABS hydraulic unit must not be loosened, with the exception of the bolt securing the cover when replacing the ABS return flow pump relay and the ABS solenoid valves.
- Welding using electrical welding equipment can affect the ABS/EDL system.
- Make sure the battery negative (-) cable is disconnected when resistance (spot) welding or electric arc welding anywhere on the vehicle.
- Do not drive vehicle when the ABS/EDL control module harness connector is disconnected.

- Observe appropriate precautions regarding handling of brake fluid.
- Place removed parts on clean surface and cover them. Do not use fluffing cloths or rags.
- 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.

Technical information required
- Applicable electrical wiring diagram
Refer to Diagrams/Diagnostic Aids.
- Installation locations of electrical components
- Brake mechanical information
- Brake hydraulic information
- Information on repairing common malfunctions on current models (as applicable)