Description of On-Board Diagnostic System
Notes on the BMW DIAGNOSTIC SYSTEM:
Diagnosis with flash code
In the case of defects in the interfaces to other systems such as DME and EML, always also read out the defect code memories of these systems.
Troubleshooting:
Note 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.
Detect Code Storage:
If a defect occurs in the ASC system when the control unit is active (ignition on), the system is switched off immediately and the ASC multi-function lamp activated. If a defect is detected during a current control function, the ASC system is switched off after the end of the control function, however, the ASC multi-function lamp is activated immediately.
Defects at the wheel sensors can only be stored during vehicle operation at speeds above 12 km/h. 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 system remains switched off if the defect has not been rectified before the next start (ignition on). If, however, this is not the case, the ASC once again assumes standby mode.
The stored defect code remains set in the defect code memory until it is either cleared (refer to "clearing defect code memory") or overwritten by another defect code. There are 9 different defect codes, however, only one can be stored at a time.
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 least 1 second and then release ASC button and brake pedal
Note:
The steps to activate the flash code must be repeated it the ASC multi-function lamp remains on.
Reading out the flash code:
The flash code is output for approx. 25 seconds irrespective of which defect code is stored.
After activation of the defect code, the ASC multi-function 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 25 seconds) when the ASC multi-function 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)
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 the point "other system defects".
- Note down number of flash pulses
- In order to exclude the possibility of the 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 lest 20 seconds at a speed in excess of 30 km/h or for at least 3 seconds at a speed above 50 km/h.
- When 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 right wheel by hand in forward direction
Reaction: The engine speed must drop noticeably
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).