Hydraulic Unit Check

Required Special Tool: 

• MB991502: Scan Tool
  CAUTION:

  • The roller of the braking force tester and the tire should be dry during testing.
  • When testing the front brakes, apply the parking brake. When testing the rear brakes, stop the front wheels with chocks.

1. Jack up the vehicle. Then support the vehicle with rigid racks at the specified jack-up points or place the front or rear wheels on the rollers of the braking force tester.
2. Release the parking brake, and feel the drag force (drag torque) on each road wheel.

   When using the braking force tester, take a reading of the brake drag force.

   CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
3. Turn the ignition switch to the "LOCK" (OFF) position and set scan tool MB991502 as shown in the illustration.
4. After checking that the shift lever/selector lever is in neutral, start the engine.
5. Use scan tool MB991502 to force-drive the actuator.
   NOTE: The TCL system will switch to the scan tool mode and the ABS warning light will illuminate.
   NOTE: When the TCL has been interrupted by the fail-safe function, scan tool MB991502 actuator testing cannot be used.
   Fig 1: Connecting Scan Tool To Data Link Connector

   Courtesy of DAIMLERCHRYSLER CORPORATION
   Fig 2: Scan Tool Actuator Test Chart

   Courtesy of DAIMLERCHRYSLER CORPORATION
6. Turn the wheel by hand and check the change in braking force. Use a braking force tester. The braking force reading value should change when the actuator test is carried out. The result should be as shown in the diagram above.
7. If the result of inspection is abnormal, replace the hydraulic unit.