Brakes - ABS Sensor Lead Faults and Repair Procedure
Group 34Brakes
Bulletin Number
34 03 93 (3857)
Woodcliff Lake, NJ
September 1993
Product Engineering
SUBJECT:
ABS Sensor Lead Faults - Repair Procedure
MODELS:
3 Series (E36), 8 Series (E31)
Situation:
Repair leads are available for the wiring harness side of the ABS sensor leads for E36 and E31 vehicles, in the same fashion as the repair leads for E30, E32, and E34 models (refer to S.I. 34 01 89 (1850)).
In most cases a fault in a sensor lead will show up as an intermittent fault (ABS warning lamp comes on while driving).
If the ABS warning lamp is continuously illuminated after starting the vehicle, the BMW Service Tester should be used to diagnose the problem.
Parts Information:
Part numbers for repairing ABS sensor leads in E31 and E36 vehicles. See illustration.
Diagnostic Procedure:
1) Disconnect the 55-pin connector from the ABS/ASC/ASC+T Control Module.
2) Connect the Universal Adaptor to the harness using the appropriate adaptor lead.
3) Using a Fluke 83 Multimeter (or equivalent) check the resistance of the individual sensor leads (refer to appropriate ETM for proper pin numbers).
The resistance should be between 65-1,600 ohms.
Wiggle and tap the connection of the sensor lead/sensor.
If a fault is not detected, try cooling the lead and connector, followed by wiggling and tapping the sensor lead/sensor.
If a fault is still not detected, repeat this procedure, heating (with a hot air gun) the lead and connector.
Repair Procedure:
Read through the entire procedure before proceeding.
1) Separate the plug connector for the ABS wheel speed sensor from the car's wiring harness, and connect it to the repair cable.
2) Detach the plug from the defective cable, insulate the defective cable and tie it back into the wiring harness.
3) Run the repair cable along the wiring harness as far as the ABS or ABS/ASC/ASC+T control unit.
Trim to the correct length for connection to the plug housing (see attachment with wiring installation diagram for the vehicle concerned).
4) Pull a shrink-fit tube (61 13 1 379 833) over the repair cable.
5) Take care not to damage the insulation of the sensor line inside, strip about 100 mm (4 in.) of insulation from the repair cable.
6) Unwind the screening from the sensor line and twist is together with one wire of the cable. Use the insulating sleeve to insulate the twisted cable.
7) Push on the shrink-fit tube at the transition point between the two insulated wires in the cable and the outer insulation.
8) Remove the insulation from the ends of the sensor line and the screening, and crimp on the flat-pin sockets.
9) Take the cover off the 55-pin wiring harness plug. Remove the side housing retainer (see E36 repair manual, Construction group 61-13/6).
Take the two connections for the defective sensor line out of their pin compartments one after the other, and insert the two flat pin sockets on the repair cable into the corresponding positions.
Caution:
It is important to perform this work in succession, first on one wire and then the other, because if the wires are accidentally interchanged, the ABS will malfunction and the car's braking performance could be affected.
10) After detaching the two wires from the car's wiring harness from their pins, remove them from the 55-pin wiring harness plug and ground them by screwing them to the control unit mount (if this is not done, the unwanted wires may have a signal-transmission effect which could once again lead to the ABS malfunctioning).
11) Reassemble the wiring harness plug.
12) It is essential for the ABS fault memory to be read out/erased at this stage, and an ABS function test to be performed.
If any wires are accidentally switched and connected improperly, the ABS may react over-sensitively or cause the car to swerve and individual wheels to lock when an ABS brake application is made.
For this reason, perform the following tests using diagnostic diskette V12.0 (ABS/ASC Tester must also be used if the vehicle being repaired is an E31 and does not have the ABS/ASC or ABS/ASC+T control module on the diagnostic link):
- Proceed to menu item 4 (Test Procedure)
- Perform Test # 1 - Checking for incorrectly connected wheel speed sensors.
- Perform Test # 3 - Function Test - Hydraulic Assembly
Correct operation of the ABS should always be checked after performing an ABS repair during a test drive.
Warranty Information:
Labor and/or parts covered under the terms of the applicable BMW New Car Limited Warranty for defects in materials or workmanship.