Antilock Brake System Components, BOSCH 5, From My 96
Function
With the start of model year 1996, the new Bosch 5 ABS system is standard equipment. In addition, an ABS/EDL system, or a traction control system (ASR) in conjunction with ABS/EDL is available for front wheel drive vehicles as optional 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 ASR traction control system prevents the drive wheels from spinning during acceleration by reducing the engine output, and is active over the entire vehicle speed range. The ASR can be switched off and on using the ASR switch in the center console. If the ASR has been switched off while driving and is not switched on again, it is automatically activated when the ignition is switched on the next time. If the ASR is switched off, the ASR warning lamp in the instrument cluster comes on. The warning lamp flashes three times a second during a control cycle.
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 (w/EDL) -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 (w/EDL) -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, the ABS, and the ASR if so equipped, are 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, ABS/EDL or ABS/EDL/ASR system has On Board Diagnostic (On Board Diagnostic) capability. The term On Board Diagnostic (On Board Diagnostic) refers to the electrical and electronic components of the system; in other words, only malfunctions that affect electrical signals are recognized.
The ABS system is able to distinguish 19 different sources of malfunction. The number of recognizable sources of malfunction increases to 24 in the ABS/EDL configuration, and to 29 in the ABS/EDL/ASR configuration.
The capabilities of the On Board Diagnostic (On Board Diagnostic) 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 (On Board Diagnostic) 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 On Board Diagnostic program if the vehicle is moving at a speed greater than 2.75 km/h (approx. 2 mph). The On Board Diagnostic program is terminated if the vehicle speed rises above 20 km/h (13 mph).
No ABS or ABS/EDL control cycle is possible during the On Board Diagnostic (On Board Diagnostic) program sequence. The ABS warning light -K47- and the red brake warning light come on. If the vehicle is equipped with ASR, the traction control indicator light -K86- also comes on.
Self-test
Each time the ignition is switched on, the system conducts a self test. The yellow ABS warning light -K47- comes on to indicate that this self-test is being conducted. If so equipped, the traction control indicator light -K86- also comes on. The warning lamps go 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.
If a malfunction is detected that does not relate solely to the ASR, then the ABS, ABS/EDL or ABS/EDL/ASR system is switched off automatically for the appropriate period.
The yellow ABS warning light -K47- and the red brake warning light in the instrument cluster come on. If equipped with ASR, the traction control indicator light -K86- also comes 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 that is related solely to the ASR is detected, "only" the traction control indicator light -K86- comes on, and the ASR is switched off automatically.
The ABS/EDL system remains operational if a malfunction is detected that is related to the ASR.
Variations of these functions exist in the case of a malfunction in the wiring between ASR push-button switch and the ABS Control Module (w/EDL) -J104- :
If an open circuit in the wiring exists, the push-button switch does not operate.
If a short circuit to positive exists, the traction control indicator light -K86- comes on for 5 minutes after "Ignition on." After this, the warning lamp goes out and the ASR is operational.
If a malfunction occurs in the power supply, i.e. the power supply drops below a permissible level, the ABS, ABS/EDL or ABS/EDL/ASR 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 (On Board Diagnostic) 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 (On Board Diagnostic) 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 section that follows describes On Board Diagnostic (On Board Diagnostic) using the scan tool :VAG1551 , electrical testing, and testing the :VAG1551 power supply and diagnostic cables.