ABS - OBD Procedure for Use With VAG 1551 Scan Tool: Overview
Group: 01Number: 94-02
Date: April 30, 1994
Subject:
On Board Diagnostic (OBD), ABS brake system
Model(s):
90 CS Quattro Sport from 1994 m.y.
Anti-lock Brake System (ABS) Model Year 1994
Beginning with the 1994 Model Year, the ABS system with On Board Diagnostic (OBD) is available on vehicles with all wheel drive.
The ABS Combination Relay - J156 and the ABS Acceleration Switch - F113 are eliminated beginning with the 1994 model year.
The ABS Control Module is equipped with a Diagnostic Trouble Code (DTC) Memory. This Technical Bulletin describes the OBD procedure for use with the VAG 1551 Scan Tool (ST).
Function
The On Board Diagnostic (OBD) function is concerned with the electrical and electronic components of the anti-lock brake system, i.e. the diagnosis procedure only detects malfunctions affecting the electrical signals.
The ABS Control Module - J104 is equipped with a DTC Memory. If any malfunctions occur in the sensors or components monitored by the system, these are stored in the memory.
The first test step is always to read the Diagnostic Trouble Code (DTC) Memory
Notes:
^ When switching on the ignition and when driving (at 5-6 km/h) the switching of the relay and start-up noise of the hydraulic unit return pump (self-check) should be heard. Do not replace the hydraulic unit due to complaints about this noise. Another noticeable self-check is through a slight vibration felt at the brake pedal
^ If a malfunction is detected the ABS switches off automatically and ABS Warning Light - K47 comes on in. the instrument cluster. The normal brake system remains fully operational. The ABS remains switched off during this trip with the exception of a malfunction in the voltage supply (in this case, the ABS switches on again as soon as the on board voltage has resumed a normal level).
^ If a malfunction (which was possibly detected and stored in the memory during the last single trip) is no longer present after the ignition has been switched off and on again, or if it cannot be detected with the vehicle stationary (certain malfunctions can only be detected when the vehicle exceeds a road speed of 12 km/h), the ABS Warning Light - K47 goes out 2 seconds after the ignition is switched on (as soon as the ABS self-check routine has been completed by the Control Module - J104) provided that no malfunction is detected.
^ If no further malfunctions are present, the malfunction stored in the memory as a static malfunction is converted to a sporadic malfunction after switching the ignition off and on.
^ A sporadic malfunction is automatically erased if it does not recur for a certain amount of single trips (ignition switched on and off again).
^ "Sporadic malfunctions" are also specially identified as such by the indication of "SP" on the right of the display on VAG 1551.
^ After processing the information inputs, the ABS Control Module - J104 distinguishes between 13 different types of malfunctions and stores them in the memory until the memory is erased (after reading) using the Scan Tool VAG 1551.
^ The OBD feature can only be utilized with the aid of the Scan Tool VAG 1551 in operating mode 1 "Rapid data transfer"
^ The OBD feature for ABS can be used not only for storing, reading and erasing malfunctions in the memory but, together with the Control Module identification and the measuring value block, offers additional facilities. The operating mode 2 "Blink Code Output" is not possible with the ABS Control Module - J104. Other operating modes possible with VAG 1551 are described in the corresponding operating instructions.
^ Data output (of OBD) is possible via the Scan Tool VAG 1551 only when the ignition is switched on or when the engine is running.
^ OBD can only be started when the vehicle is stationary (if vehicle is traveling at more than 2.5 km/h the ABS Control Module - J104 does not respond).
^ Reading and erasing the DTC Memory, Control Module identification and reading the measuring value block are only possible up to a speed of 20 km/h (OBD is stopped if this speed is exceeded).
On Board Diagnostic (OBD), technical data
^ Diagnostic Trouble Code (DTC) Memory
- The contents of the permanent memory are retained even when the supply voltage is switched off.
^ Data output
- Rapid data transfer (operating mode 1)
- Blink code output is not provided.
- The ABS Warning Light in the instrument cluster lights up when the ABS is switched off.
^ Functions
- Read Control Module versions (01).
- Read DTC Memory (02)
- Erase DTC Memory (05)
- Read measuring value block (08)
- End output (06).
Number inside ( ) is the function code
Notes:
^ During OBD no control function is possible (ABS Warning Light - K47 lights up); for this reason, OBD is interrupted as soon as the vehicle is travelling at more than 20 km/h).
^ The "Output Diagnostic Test Mode" function is not possible with OBD. The appropriate tests must be performed with the ABS tester VAG 1710 according to the troubleshooting program (with function test).
^ Installed location of components Repair Group 45
Safety precautions and general notes on troubleshooting
^ The ABS is a safety system: knowledge of the system is required when performing repairs or other work.
^ Always interrogate (read) the Diagnostic Trouble Code Memory before performing any work on the ABS system.
^ Do not drive the vehicle when the harness connector is disconnected from the ABS Control Module.
^ Ignition must be switched off when disconnecting or connecting harness connectors.
^ Do not loosen bolts on hydraulic unit (this does not apply to the relay cover).
^ Observe normal safety precautions when working with brake fluid - Repair Group 47.
^ Malfunctions in the ABS system are indicated by the ABS Warning Light; certain malfunctions are only recognized when the vehicle exceeds a speed of 12 km/h (perform road test).
^ For information on repairing actual malfunctions, Repair Manual.
Test Requirements
^ Same tire sizes (as specified) on all four wheels; tires inflated to specified pressures.
^ Conventional brake system functioning properly, including Brake Light Switch, Left and Right Brake Lights.
^ No leaks from hydraulic connections or lines (visual check of hydraulic unit, brake cylinder).
^ Wheel bearing and wheel bearing play OK.
^ Ground connection for ABS Return Flow Pump V39 on hydraulic unit OK
^ ABS Return Flow Pump Relay - J105 and ABS Solenoid Valve Relay - J106 correctly connected.
^ Harness connector on ABS Control Module - J104 correctly connected (positive engagement).
^ When working with the Scan Tool VAG 1551, the test box VAG 1598 must not be connected to the ABS Control Module - J104.
^ Function of manually engaged differential lock OK (Rear Differential Lock Indicator Light - K46 lights up when engaged and goes out completely when switched off).
^ Differential lock not engaged.
^ All fuses OK - per wiring diagram
^ Supply voltage OK (at least 10.5 V)
Required technical information
^ Appropriate wiring diagram
^ Technical Bulletin, Group 45, No. 94-01, "ABS, checking function with VAG 1710"