Description of On-Board Diagnostics

Troubleshooting:

Notes on the BMW DIAGNOSTIC SYSTEM:

Important!

Only the ABS/ASC+T control unit with the BMW No.1 159 494 (crimson red adhesive label) can be read out with the BMW DIAGNOSTIC SYSTEM.

This variant is installed in vehicles with manual transmission and as of Approx. 9/90 also in vehicles with electronic transmission control.

The following diagnostic functions are possible with this control unit:
- Read control unit identification
- Read detect code memory
- Clear defect code memory

Diagnosis with the ABS/ASC+T control unit with the BMW No.1158 804 (red-violet adhesive label) is only possible via the flash code.

If a defect occurs in the vicinity of the interfaces to the other systems (DME, EML, EGS), the defect code memory of the system concerned should always be read out with the BMW DIAGNOSTIC SYSTEM in the case of both control unit variants.

In addition to the ABS/ASC+T control unit, the EGS is also supplied by the EML with the DKV signal. This signal can be read out with the BMW DIAGNOSTIC SYSTEM using the EGS diagnostic program under point "Status display".

Notes on Differentiation between ABS/ASC and ABS/ASC+T:

The ABS/ASC+T system can be identified by the plunger hydraulic unit which is arranged in the engine compartment above the left-hand engine mount or by its vent connection on the left-hand side in the engine compartment.

The following test instructions are to be used corresponding to the variant:

ABS/ASC

ABS/ASC+T

Defect Code Storage:

If a defect occurs in the ABS or ASC+T system when the control unit is active (ignition ON), this defect is stored permanently and the relevant system or the entire system is switched off. Defects at the wheel sensors can only be stored when the vehicle is driving at speeds in excess of 12 km/h. All faults which result in the ABS system switching off also cause the ASC+T system to switch off, i.e. all ABS components are monitored by the ASC+T system.

However, the ABS system is not switched off in the case of every defect in the ASC+T system. If two or more defects occur simultaneously, the one with the highest priority is stored. The lower the number of flash pulses, the higher the priority of the defect.

The ABS/ASC+T system is fully operable once again If the defect no longer exists at the next start (ignition ON). The defect code still remains stored in the defect code memory until it is either cleared (see "Clearing defect code memory") or it is overwritten by another defect code.

There are 20 different defect codes, however, only one can be stored at a time.

With the ABS/ASC+T control unit BMW No.1 159 494 (diagnostic capabilities via the diagnostic links), 3 different defect codes from a total of 22 can be stored at any one time.

Note:

In extreme driving situations (skidding) with the ASC+T system switched off, it is possible that the ABS system cuts out and the defect code 14 (valve relay) is stored. Simply clear the defect code memory in this case.

Defect Code Memory Readout:

Activating the flash code:



- Switch off ignition
- Press ASC button and depress brake pedal simultaneously
- Hold ASC button and brake pedal depressed simultaneously and switch on ignition
- Keep depressed for at leas 1 second and then release ASC button and brake pedal

Notes:

The steps to activate the flash code must be repeated If the ASC lamp remains on.

Reading out the flash code:



The flash code is output for Approx. 47 seconds irrespective of which defect code is stored.

After activation of the defect code, the ASC lamp goes out for 3 seconds and then begins outputting the flash pulses at a flash frequency in a pulse/pause ratio of 1 sec/1 sec.

The number of flash pulses indicates which defect code is stored. Refer to the table of defect codes below.

Example:

2 flash pulses (BI) = Defect code 02

Clearing Defect Code Memory:

There are three possible ways of clearing the defect code memory:

Within 3 seconds after the end of the flash code output (after 47 seconds) when the ASC lamp lights permanently once again, press the ASC button for at least 1 second.

Disconnect vehicle battery (Attention! Defect code memories of other systems may be cleared).

Disconnect control unit (Attention! Ignition must be switched off). In the case of ABS/ASC+T control unit with BMW No.1 159 494 (diagnostic capabilities via the diagnostic links), the contents of the defect code memory can be cleared with the BMW DIAGNOSTIC SYSTEM. The contents of the defect code memory are not deleted If the control unit is disconnected.

Troubleshooting Procedure:

- Check system for mechanical and hydraulic defects
- Read out defect code memory via flash code

Note:

If the defect code cannot be read out, then continue troubleshooting as described under point "Other system defects".

- Note down number of flash pulses
- In order to exclude the possibility of any counting errors, read out the defect code memory once again
- Clear defect code memory
- Perform troubleshooting with schematic
- Rectify defect
- Perform test run

Note:

During the test run, the car should be driven for at least 20 sec at a speed in excess of 30 km/h or for at least 3 seconds at a speed above 50 km/h.

- If defect code is stored once again, repeat procedure until no defect code is stored.

Simulating ASC Control Mode:

- Raise vehicle on floor jack (all wheels must turn freely)
- Set automatic selector lever to "neutral (N)"
- Start engine
- Set engine speed by means of accelerator pedal or adapter EML No. 12.7010 to Approx. 2000 rpm
- Quickly accelerate rear left or rear right.wheel by hand in forward direction

Reaction: Braking of the turned wheel must be felt.

Dynamic Testing of the Speed Sensors:

Uniform Progression of Speed Signal (Signal OK.):

Connect oscilloscope of BMW Service Tester as follows:

- Terminal D+ blue to speed sensor signal
- Frequency (-) black to speed sensor ground
- Frequency (+) blue to terminal 1 black

*M* 13 select frequency and enter 80 Hz

*M* 22 select oscilloscope

Uniformly turn wheel by hand. A sinusoidal curve must appear (amplitude and period duration change depending upon the rotary speed).

Checking for interchanged Wheel Speed Sensors:

Perform dynamic wheel speed sensor test in accordance with Schematics or to "Pin Assignments" at each wheel.

If no signal can be seen on the oscilloscope from one wheel, turn the opposite wheel. If a signal is displayed, this indicates that the wheel speed sensor wiring has been interchanged.





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*M*: Multimeter; Select multimeter on the BMW SERVICE TESTER. Select indicated multimeter function.