ABS Activates During Light Brake Application – 1996-2005 Audi

45 ABS activates during light brake application

 

45 08 04  2010096/3  November 19, 2008. Supersedes Technical Service Bulletin Group 45 number 05-01 dated March 1, 2005 for reasons listed below.

 

Model(s)	Year	VIN Range	Vehicle-Specific Equipment
A4	1996 – 2001	All	Not Applicable
A6	1998 – 2004	All
Allroad Quattro	2000 – 2005	All
A8	1998 – 2002	All

 

Condition

REVISION HISTORY

Revision	Date	Purpose
3	–	•     Revised Title to add Repair Group •     Reformatted

 

ABS activates when braking lightly or control noises are heard from the ABS unit at low speed without brake application.

 

Technical Background

May be caused if an ABS control takes place without the flashing of the ESP lamp and thus without ESP operation.

• This is purely an ABS action.
• The ESP sensors have no influence on this.

The following may be the cause for incorrect wheel speed values:

• Damaged wires from the wheel speed sensor to the ABS control unit.
• Tires of unequal size or greatly unevenly worn tires.
• Slight cracks in the ABS rotors (especially on older vehicles).
• Dirty or incorrectly adjusted wheel speed sensors.

 

Production Solution

Service

Do not replace any components until the following has been performed.

Tip: DTCs may not be stored in the ABS control module, and On-Board Diagnostic (OBD) Read measuring value block 1 may not show any deviation in the wheel speed value.

1. Thoroughly check the ABS for any cracks, debris or damage to ensure proper operation.

Note:

Since slight cracks may be hard to detect with a naked eye, use an oscilloscope.

2. Using an oscilloscope (VAS 5051), check the wheel speed values.
   • Curve and frequency must be smooth and uninterrupted as shown in Figure 1.

Figure 1. Smooth curve and frequency.

 

• A short disruption (such as a scratch or a notch) in the curve of the DSO picture that is repeated periodically may indicate a damaged ABS rotor. If a short disruption is observed, inspect the ABS rotor for damage. The ABS rotor may be located on the outer CV joint, the wheel hub, or the inside of the brake disc. (See Repair manual >> Group 45 – Anti–lock brake system ).

Figure 2. A short disruption in the curve and frequency repeated periodically.

 

Warranty

This TSB is informational only and not applicable to any Audi warranty.

 

Additional Information

All parts and service references provided in this TSB are subject to change and/or removal. Always check with your Parts Department and service manuals for the latest information.