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Circuit Tests

NOTE: To avoid damage to ABS harness connector pins, manufacturer recommends using VAG 1598/20 Test Box (breakout box) to carry out measurements. Terminal number designations on Test Box (VAG 1598/20) are identical to ABS control module harness connector terminals.

  1. Check Voltage At ABS Control Module

    Turn ignition on. Measure voltage between Test Box (VAG 1598/20) terminals No. 15 and 19. Reading should be 10.0-14.5 volts. If reading is not within specification, check for continuity to ground at terminal No. 19. Also, check power supply at terminal No. 15. If readings are not as specified, check affected circuit for an open or shorted condition.

  2. Check Voltage At ABS Hydraulic Unit

    Turn ignition on. Measure voltage between Test Box (VAG 1598/20) terminal No. 16 and terminals No. 17 and 18. Readings should be 10.0-14.5 volts. If readings are not within specification, check for continuity to ground at terminal No. 16. Also, check power supply at terminals No. 17 and 18. If readings are not as specified, check affected circuit for an open or shorted condition.

  3. Brakelight Switch

    Measure voltage between Test Box (VAG 1598/20) terminals No. 14 and 19. Reading should be 0-5 volts with brake pedal released. With brake pedal depressed, reading should indicate 10.0-14.5 volts. If readings are not within specification, check for continuity to ground at terminal No. 19. Also, check power supply at terminal No. 14. If readings are not as specified, check affected circuit for an open or shorted condition.

  4. Right Front Wheel Speed Sensor

    Turn ignition off. Measure resistance between Test Box (VAG 1598/20) terminals No. 3 and 5 (FWD with ABS/ASR) or terminals No. 4 and 5 (FWD or Quattro with ABS/EDL). Resistance should be 400-2300 ohms. If resistance is not within specification, check wheel speed sensor harness circuit for open, short to ground and short to power. Also check harness connector at suspect wheel speed sensor. See WIRING DIAGRAMS . Repair if necessary. If wiring is okay, replace suspect wheel speed sensor.

  5. Left Front Wheel Speed Sensor

    Turn ignition off. Measure resistance between Test Box (VAG 1598/20) terminals No. 6 and 7. Resistance should be 400-2300 ohms. If resistance is not within specification, check wheel speed sensor harness circuit for open, short to ground and short to power. Also check harness connector at suspect wheel speed sensor. See WIRING DIAGRAMS . Repair if necessary. If wiring is okay, replace suspect wheel speed sensor.

  6. Right Rear Wheel Speed Sensor

    Turn ignition off. Measure resistance between Test Box (VAG 1598/20) terminals No. 1 and 3 (FWD with ABS/EDL) or terminals No. 1 and 2 (FWD with ABS/ASR and Quattro with ABS/EDL). Resistance should be 400-2300 ohms. If resistance is not within specification, check wheel speed sensor harness circuit for open, short to ground and short to power. Also check harness connector at suspect wheel speed sensor. See WIRING DIAGRAMS . Repair if necessary. If wiring is okay, replace suspect wheel speed sensor.

  7. Left Rear Wheel Speed Sensor

    Turn ignition off. Measure resistance between Test Box (VAG 1598/20) terminals No. 8 and 9. Resistance should be 400-2300 ohms. If resistance is not within specification, check wheel speed sensor harness circuit for open, short to ground and short to power. Also check harness connector at suspect wheel speed sensor. See WIRING DIAGRAMS . Repair if necessary. If wiring is okay, replace suspect wheel speed sensor.
    NOTE: When VAG 1551 scan tool is connected and has established communications with ABS control unit, the ABS warning light, Red brakelight and ASR warning light (if equipped) will be illuminated.

  8. ABS Warning Light Inoperative

    Ensure no ABS related DTCs are stored in memory. Turn ignition off for at least 10 seconds. While observing ABS warning light, turn ignition on. ABS warning light should illuminate for 2 seconds. If ABS warning light does not illuminate, measure voltage between ground and Test Box (VAG 1598/20) terminal No. 21. If voltage is not present, substitute a known-good ABS control unit and retest. If battery voltage is present, check circuit to instrument panel. See WIRING DIAGRAMS . If circuit to instrument panel is okay, check for a defective bulb or replace instrument panel processor.

  9. Red Brake Warning Symbol

    Ensure Red brake warning light is not being activated by brake fluid level sensor, brake pad wear indicators or parking brake switch. Disconnect a front wheel speed sensor. Turn ignition on. Connect scan tool and select "Output Diagnostic Test Mode - 03". If ABS warning light and Red brakelight illuminate, Red warning light circuit is okay. If Red warning light does not illuminate, repair malfunction in instrument panel or instrument panel processor.
    NOTE: Steps 10)  and 11)  apply only to vehicles equipped with ASR.

  10. ASR Warning Light

    Using scan tool, ensure no related DTCs are stored in memory. Turn ignition off. Install Test Box (VAG 1598/20) to ABS control module. Turn ignition on. ASR warning light should illuminate for about 2 seconds. If ASR warning light does not illuminate, or stays illuminated continuously, check circuit from terminal No. 20 of ABS control module to instrument panel processor connector for an open or shorted condition. See WIRING DIAGRAMS . If circuit is okay, check for an open bulb or faulty instrument panel processor.

  11. ASR Push Button Switch

    Check operation of ASR switch. Turn ignition off. Install Test Box (VAG 1598/20) to ABS control module. Turn ignition on. Operate ASR push button switch. ASR warning light should illuminate. Depress ASR push button again, ASR light should turn off. If ASR light does not function as described, measure voltage between terminals No. 19 and 31. With ASR switch released, reading should be 0-5 volts. With ASR switch depressed, reading should 10.0-14.5 volts. If readings are not as specified, check ground circuit from terminal No. 19 and power circuit from terminal No. 31. Repair as necessary. If circuits are okay, replace ASR switch.
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