Brakes - False ABS Warning Lamp Illumination
89BMW05Group 34 Brakes
Bulletin Number 34 02 89(1857) Page 1 of 3
Woodcliff Lake, NJ August 1989 Technical Dept.
SUBJECT: ABS Warning Lamp Illumination
MODEL: 1988 325iX (up to and including 5/88 production)
Observation: The ABS system on the 325iX incorporates an additional function to reduce engine braking (at closed throttle) when ABS is activated on low drag coefficient road surfaces.
The ABS Control Unit sends this request via pin 3 to pin 50 of the DME Control Unit.
As part of the ABS self-check, this circuit is continuously monitored. If the control unit determines that the circuit is open or has high resistance the ABS system will be deactivated and the ABS warning lamp will be illuminated.
Situation: Tolerances in DME circuitry (pin 50) can cause this condition to occur. An adapter harness is available to compensate for these tolerances.
DME 1.3 control units do not have circuitry compatible with the ABS control units originally installed in these vehicles. For this reason an adapter harness must be installed whenever a DME 1.3 control unit is installed into one of these vehicles.
DME 1.1 control units may also exhibit the same problem. To determine if the problem lies in the circuit (or elsewhere in the ABS system) perform the following diagnostic steps.
Note: Call up the DME system via the BMW Service Tester for positive identification of the control unit (1.1 vs. 1.3).
Diagnostic
Procedure: Tools required: Universal Adaptor w/35 pin adaptor leads
Fluke multimeter
^ Connect universal adaptor between ABS control unit and harness.
^ Connect multimeter between pin 3 (+) and pin 10 (-).
^ Start engine and observe voltage.
^ If the voltage is 1.23 or higher an adaptor harness must be installed.
If below 1.23V the problem is elsewhere via the ABS system. Use the BMW Service Tester to diagnose the system.
Harness Installation:
1) Disconnect the engine harness from the vehicle harness at C101.
2) Remove connector holder from the firewall and install the additional mounting bracket.
3) Install both connector holders to this bracket.
4) Connect adaptor harness between the engine and vehicle harness.
5) Secure connector housing in the appropriate connector holders.
6) Attach the ground lead on this adaptor harness to the hood catch as shown.
Parts
Information: Included in one kit (P/N 12 52 9 061 634) is an adaptor harness and mounting bracket.
Warranty Information:
Part and labor covered under the terms of the BMW New Car Limited Warranty of 3 Years/36,00 Miles.
Defect code: 34 52 00 12 00
Labor operation: 00 50 161 - diagnosis
Labor allowance: 4 FRU
Labor operation: 00 50 759 - harness installation
Labor allowance: 1 FRU
Labor operation: 00 50 760 - testing operation of ABS system
Labor allowance: 3 FRU