Finding the Problem!

Diagnostic Equipment
In addition to the BMW Service Tester, various manufacturers have produced diagnostic equipment compatible with BMW diagnostic systems. Although some differences exist between the range of capabilities, procedures and displays, these testers are capable of analyzing the BMW Antilock Brake System (ABS). Equipment recognized at the time of this publication include:

- BMW ABS/ASC Tester by BMW
- BMW SERVICE Tester and ABS Adapters by BMW
- BOSCH ABS Tester by Robert Bosch
- ABS2000 offered by BAUM TOOLS

Typical diagnostic testers usally have differences in diagnostic capabilities. Therefore, application of testing procedures may vary. Always follow the directions and procedures provided by the equipment manufacturer.

Troubleshooting
All Troubleshooting must begin by checking the basics. Checking the Basics.

Troubleshooting without a thorough understanding of the ABS operation may lead to misdiagnosis and needless expense. The troubleshooting technician should review the Description and Operation provided at the system and component levels and systematically follow all test instructions. Specialized training and diagnostic test equipment are recommended. Description and Operation.

Electronic Diagrams should always be used since they clearly show the interaction of various components or systems. Technical Service Bulletins should be consulted for additional information.

If the ABS Warning Lamp Illuminates Intermittently, and Normal Troubleshooting Procedures Do Not Indicate a Defect, Check the Tire Sizes. Differences in tires may cause enough variance in rolling diameters to confuse the ABS control unit, which may give a false signal to the ABS warning light. This is especially true if snow tires have been mounted on the rear wheels only. Verify that all four tires are of the same size and are wearing uniformly.

Test 01 - Harness/Wheel Sensor ..... Test 10 - Hydro Unit, Press-Build, Press-Retention
These test procedures are intended for use with the BMW service tester and ABS Adapter units. Equipment connections needed, expected nominal values, and troubleshooting procedures are provided for each test.

NOTE:
Although these tests are designed for use with BMW test equipment, the use of other BMW compatible testers should result in obtaining the given nominal values. Be sure to follow the procedures provided by the equipment manufacturer.

The "TROUBLESHOOTING" section of each test provides detailed instructions for situations where the nominal values are not reached. In many cases a high quality DVOM will be sufficient to conduct necessary troubleshooting.

Without Specific ABS Test Equipment
Even if specific ABS test equipment is not available, beneficial tests can be conducted. Pinpoint testing with a DVOM at the ABS harness connector, in conjunction with the "NOMINAL VALUES" and "TROUBLESHOOTING" procedures of each test, in addition to the Electrical Diagrams, will bring very helpful results.

Example From Test 01 - Harness/Wheel Sensor (extract)

Nominal Values (Circuit And Component Specs.):

Nominal Values

3. Compare the displayed actual values obtained from the test equipment with the nominal values provided above. (if 999 k Ohms flashes, this indicates > 999 k Ohms). If nominal values are not obtained, proceed with the troubleshooting procedures below as needed.

TROUBLESHOOTING

NOTE: Turn "Off" ignition for single tests, control unit not connected.

Speed Sensor (DF)
Front Left
1. Check front left plug connection (visual inspection).
2. Disconnect front left plug, DF reading must then be > 999 k-ohms; DF reading lower: defect in wire harness.
3. Check flow in wires 4 and 6: bridge front left plug on wire harness side, DF reading should then be < 1 ohm; DF reading higher: defect in wire harness.
4. Measure resistance at plug on speed sensor side. Specification not reached: replace front left speed sensor.