ABS/ASC - Warning Lights On During Dynamometer Test: Overview

Group 34
Brakes

Bulletin Number
34 02 98

Woodcliff Lake, NJ
April 1998
Product Engineering

SUBJECT:
ABS/ASC Warning Lights Illuminated During Dynamometer Test

MODEL:
8 Series (E31) 91 Model Year to 97 Model Year
7 Series (E23, E32, E38) from 85 Model Year to 8/97 production
6 Series (E24) from 85 Model Year
5 Series (E28, E34, E39) from 85 Model Year except 540iA from 9/97 production
3 Series (E30, E36) from 86 Model Year

Situation:

Many State Motor Vehicle Agencies require vehicles to be tested on a dynamometer during annual emissions testing. This test may set the ABS and ASC warning lights on the instrument cluster, and cause the vehicle owner concern.

Note that ABS/ASC warning lights are likely to be set under any conditions where the front wheels are stationary, and the rear wheels are spinning. The vehicle ABS/ASC systems will be immobilized until the warning lamps are switched off.

Cause:

The warning lights are illuminated because the ABS/ASC system sees an implausible speed differential between the spinning rear wheels, and the stationary front wheels. Note that vehicles equipped with DSC3 (E38 from 9/97, and 540iA from 9/97) will not set the ABS/ASC warning lights under these conditions.

Procedure:

The ABS/ASC warning lights will automatically switch off as follows:

^ Switch off engine
^ Wait a minimum of 30 seconds
^ Restart engine, and drive away
^ Warning lights will go out when speed exceeds 8 mph (Fault codes will be retained in memory)

Because of this mechanism for turning off the warning lights, it is unlikely that a customer will arrive at a BMW Center with the warning lights still illuminated. In case of a customer complaint, confirm with the customer the conditions when the lights were set.
If the fault was set during a dynamometer, or similar test, no further diagnosis is required.

Importantly, reassure the customer that the lights were set because the ABS/ASC system was working normally. The fact that the lights go out by themselves, confirms this.

Note 1:
For BMW Centers who have State approval to carry out enhanced I/M dynamometer testing, accurate emissions measurements, on ASC equipped vehicles, can only be made with the ASC switch switched to the "off" position.

Note 2:
This bulletin is being sent to State Motor Vehicle Agencies (Attachment 1), together with a letter which can be provided to the BMW owner (Attachment 2).