Abs With Electronic Differential Lock, BOSCH 5, From My 96
Function
With the start of model year : 1996 , the new Bosch 5 ABS /EDL system is standard equipment.
- ABS prevents the wheels locking during a brake application initiated by the driver.
- EDL is an aid to starting from a stop, which activates the electronically-controlled braking of a spinning drive wheel and switches engine output to the "gripping" wheel. EDL control operates up to a road speed of 40 km/h (25 mph).
The ABS /EDL system controls all four wheels on quattro all-wheeldrive models. The two brake hydraulic circuits are split diagonally-one supplying left front and right rear brakes with the appropriate hydraulic pressure, the other supplying right front and left rear brakes.
On quattro all-wheel-drive models, the EDL control of all four wheels makes it possible to eliminate the driver-operated mechanical differential lock for the rear differential. It is no longer used.
Control systems
The two brake hydraulic circuits are split diagonally-one supplying left front and right rear brakes with the appropriate hydraulic pressure, the other supplying right front and left rear brakes.
Matched software stored in the ABS control module -J104-, performs the function of the conventional brake pressure regulator, the latter no longer being installed.
To eliminate any risk of the brakes overheating, EDL control cycles are no longer permitted once the brakes have reached a certain temperature. The temperature limit is defined in the ABS control module -J104-. Actual brake temperature is calculated by the control module using a computed model. EDL is re-activated once the control module calculates a lower limit brake temperature based on the computed model. Operation of the brakes and the ABS is not affected by this intervention in the system.
If the brakes are hot, the control module continues to operate even after the ignition is switched off until the calculated temperature of the brakes has dropped below a fixed value; this situation continues for up to one hour. During this time, the control module operates with an increased current consumption of about 500 mA, compared to less than 0.5 mA when the control module is not operating.
On Board Diagnostic
The control module for the ABS /EDL system has On Board Diagnostic (OBD) capability. The term On Board Diagnostic (OBD) refers to the electrical and electronic components of the system; in other words, only malfunctions that affect electrical signals are recognized.
The ABS /EDL system is able to distinguish 24 different sources of malfunction.
The capabilities of the On Board Diagnostic (OBD) system are accessible by connecting the scan tool: VAG1551 in "Rapid data transfer" operating mode 1. No provision is made here for use of the "Blink code output" operating mode 2. Additional scan tool: VAG1551 operating modes are described in the relevant operating instructions.
The On Board Diagnostic (OBD) program can be started only if the vehicle is stationary and the ignition is switched on (or the engine is running). It is not possible to start the OBD program if the vehicle is moving at a speed greater than 2.75 km/h (approx. 2 mph). The OBD program is terminated if the vehicle speed rises above 20 km/h (13 mph).
No ABS /EDL control cycle is possible during the On Board Diagnostic (OBD) program sequence. The ABS warning light ABS warning light -K47- and the red brake warning light come on.
Self-test
Each time the ignition is switched on, the system conducts a selftest. The yellow ABS warning light ABS warning light -K47- comes on to indicate that this self-test is being conducted. The warning light goes out after about 2 seconds. The self-test continues after the vehicle moves off, as certain malfunctions cannot be recognized until the vehicle is moving.
The self-test may be perceived by the switching of relays, the startup noise of the return pump (ABS hydraulic unit), and by a slight vibration at the brake pedal. These system-related effects are part of the self-test program, and this should be explained to customers in the event of any complaints.
The yellow ABS warning light ABS warning light -K47- and the red brake warning light in the instrument cluster come on.
The conventional brake system remains fully operational even after a malfunction is detected. As operation of the brake pressure regulator is also affected by a failure of the ABS /EDL system, it is important to contact an Audi retailer Service department without delay.
Exceptions to this are two malfunctions: "00526 Brake Light Switch-F" (DTC TABLE => 00526 ) and "00668 Battery Positive Voltage (B+) Term.30" (DTC TABLE => 00668 ). If one of these malfunctions is recognized, only the EDL function is deactivated. None of the warning lamps comes on.
If a malfunction occurs in the power supply, i.e. the power supply drops below a permissible level, the ABS /EDL system is switched off and all the relevant warning lamps come on. The system switches on again, however, as soon as the battery positive voltage (B+) has reached a permissible level, and the warning lamps go out. (If there is a complete loss of power, an open circuit in a cable or fuse, only the ABS warning lamp comes on).
Diagnostic Trouble Code (DTC) memory
The ABS control module is equipped with DTC memory. If malfunctions occur in the monitored sensors or components, these are stored in DTC memory, which can be checked using the scan tool: VAG1551 .
The control module's On Board Diagnostic (OBD) program distinguishes between "static" and "sporadic" malfunctions. If a stored static malfunction no longer exists after the ignition is switched on, it is converted and stored as a sporadic malfunction. The one exception to this is "Control Module Malfunctioning" which is stored only as a static malfunction.
Sporadic malfunctions are identified as such by an "/SP" appearing on the right side of the scan tool: VAG1551 display.
If a sporadic malfunction no longer occurs over a certain number of driving periods, it is automatically erased.
Static malfunctions are stored until the DTC memory is erased by the scan tool: VAG1551 .
On Board Diagnostic (OBD) functions are not restricted only to storing, checking and erasing stored malfunctions. The system offers additional capabilities in terms of the "Check Control Module Versions," "Code Control Module" and "Read Measuring Value Block" functions.
The information that follows describes On Board Diagnostic (OBD) using the scan tool: VAG1551 , electrical testing, and testing the : VAG1551 power supply and diagnostic cables.