Antilock Brakes / Traction Control Systems: Service Precautions
Anti-locking brake system (ABS), anti-locking brake system with electronic differential lock (ABS/EDL) and anti-locking brake system with traction control system (ABS/EDL with TCS) Bosch 5.3
Safety precautions
WARNING: Brake fluid is poisonous.
CAUTION:
- Before working on the ABS or ABS/EDL system, disconnect the battery Ground (GND) strap. For anti-theft coded radios, first make sure that the radio code is available.
- Brake fluid must not contact painted parts.
- Brake fluid absorbs moisture from the air and must therefore be replaced every two years. Use only new, approved brake fluid that complies with MVSS 116 (DOT) 4.
- DO NOT use silicone-based brake fluid (DOT 5). Even the smallest traces can cause severe corrosion in the brake system.
CAUTION:
- Before doing any welding repairs on the vehicle using electric welding equipment, disconnect the ABS control module.
- After work that requires opening the brake hydraulic system, bleed the system. Refer to Brake systems (with and without ABS), bleeding.
- During the final road test, make sure that at least one controlled brake test is included (pulsations must be felt at the brake pedal).
- Absolute cleanliness is required when working on the ABS or ABS/EDL system. DO NOT use any products that contain mineral oil, such as oils, greases, etc.
- Thoroughly clean all connections and the immediate vicinity before loosening. DO NOT use aggressive cleaning agents such as brake cleaner, gasoline or thinners.
- Place removed parts on a clean surface and cover. DO NOT use fluffy cloths.
- Carefully seal or cover opened components if a repair cannot be completed immediately.
- Only install replacement parts that were packed in their original packaging. Only remove them immediately before installation.
- When the hydraulic system is open DO NOT work with compressed air in the vicinity and DO NOT move the vehicle.
- Take precautions to make sure that brake fluid does not enter any wiring harness connectors.
ABS layout.
The ABS brake system is divided diagonally. Brake-assist is activated by the brake booster.
Hydraulic unit -a- and control module -b- are one unit and if malfunctioning must be replaced together.
New control modules supplied as replacement parts are coded. However, not control modules with traction control system (TCS).
Illustration: Shows the ABS layout in a right-hand drive vehicle.
Connecting brake lines from master cylinder to hydraulic unit
A Secondary piston circuit
B Primary piston circuit
1 Hydraulic unit to left rear wheel cylinder/brake caliper
2 Hydraulic unit to right rear wheel cylinder/brake caliper
3 Hydraulic unit to right front brake caliper
4 Hydraulic unit to left front brake caliper
Notes:
- Before performing anti-lock system repair work, determine malfunction cause through On Board Diagnosis.
- Disconnect battery ground strap with ignition switched off
- When working with brake fluid, observe safety precautions and notes.
- After repair of hydraulic system, bleed the brake system with brake filling/bleeding tool VW 1238/1 or VAG 1238 B or US 1116 or equivalent.
- During road test, perform a controlled brake test at least once (must feel pulsations at the brake pedal).
- Absolute cleanliness is required when working on the anti-lock brake system, do not use any products which contain mineral oil, such as oils, greases etc.
- Thoroughly clean all unions and adjacent areas before loosening, do not use aggressive cleaning agents such as brake cleaner, thinners or similar
- Place removed parts on a clean surface and cover.
- Carefully cover or seal open components if repairs are not completed immediately (Use plugs from repair kit 1 H0 698 311 A).
- Use only lint free cloth.
- Remove replacement parts from packaging only prior to installation.
- Only use original packed parts.
- When the system is open do not use compressed air and do not move the vehicle.
- Ensure that no brake fluid enters harness connectors.
- During painting, the ABS control module can be exposed to a max. temperature of 95°C (203°F) for only a short period, and to a maximum of 85°C (185°F) for longer periods (approximately 2 hours).