SRS Diagnostics - Jeff Cocking


This is the instructions for diagnosing the SRS system from the BMW 633csi - M6 US 1983-1989 Repair manual.  I would also suggest you try How to correct and extinguish the SRS warning light on an 88/89.  I used this approach and it fixed my problems.  Of course this is after I went through all the diagnosis listed below.   All items in italicize are mine for clarification.

The "supplement restraint system" employs a defect detector and memory, even for briefly occurring defects. If the "SRS" indicator lamp does not go out after starting, there could be one or more defects. A flashing code from the indicator lamp will help only personnel with qualified training in BMW service to pinpoint and eliminate the defect(s).

The flashing code can be called by performing the following procedures and as often as desired.

A) Turn off ignition.

B) Connect SRS diagnosis plug 62 1250 in engine diagnosis socket (pins 1 and 6 are bridged). If necessary use adapter 62 1140.  I used a paper clip to bridge pins 1 and 6

C) Turn ignition lock to position 1.

Flashing code will now run off and the number of flashes must be counted.  Each diagnosis code is a series of four numbers marked as x-y-z-d.  The x-y-z number is used to determine actual fault and the d number indicates a brief or permanent defect.   Have a pen and paper handy.

SRS Bulb Activity Duration in Seconds Comments
  6 Bulb Test
  Flashes 1 to 3 times depending on the number of defects
 
 
   3 Dark
In case of more than one defect this section is repeated as often as the number of defects.   3 Start of defect code
  3 Dark
  Flashes 1 to 3 times - Note number.  This is the first code number (x).
 
 
  3 Dark
  Flashes 1 to 4 times - Note number.  This is the second code number (y).
 
 
 
  3 Dark
  Flashes 1 to 2 times - Note number.  This is the third code number (z).
 
  3 Dark
  Flashes 1 to 2 times - Note number. 1 time for a brief defect (short interruption of plug contact) and 2 is for a permanent defect. This is the type of defect number (d).
 
  3 Dark
  3 Break/Start with more than 1 defect repeat.  If another code is in the system it will start here. Same format as above x-y-z-d.   Lamp on continuously - end of control check.



DEFECT CODE TABLE

X number Y number Z Number Related Defect Code
1 1 1 B
1 1 2 A
1 4 1 H
1 4 2 G
2 1 1 K
2 1 2 J
2 2 1 M and L
2 3 1 O
2 3 2 N
2 4 1 Q
2 4 2 P
3 1 1 S
3 1 2 R
3 2 1 U
3 2 2 T
3 3 1 W
3 3 2 V
3 4 1 Y
3 4 2 X

TESTING INSTRUCTIONS

After finishing the flashing code call, always disconnect the battery for troubleshooting and cover the negative pole or terminal. Make tests with a BMW service tester or digital tester II at room temperature. Using different testers could activate the SRS. Pull off the SRS diagnosis plug.

After finishing repairs the last step would be connecting the battery again and checking the function of the system.

If there is a brief defect, cancel the memory of the diagnosis unit by disconnecting and connecting the battery. Check pertinent parts for tight fit and damage with the ignition on. Replace pertinent parts, if a defect is displayed.

Defect Code Instructions      
A or B Higher or lower resistance in gray-white/gray wire to SRS unit.      
  Disconnect plug (next to diagnosis unit in glove box).   Connect SRS test plug 62 1 260 and check wire with an ohmmeter.  3.0 to 5.0 ohms? If Yes, Defect A: Measure resistance of wire against car ground.   Resistance 200 to 600 ohms? If Yes, go to default code H.
If No, Replace diagnosis unit.
Defect B:  Replace diagnosis unit.  
  If No, Disconnect plug (on steering column). Connect SRS test plug 62 1260 and check wire with an ohmmeter.
3.0 to 5.0 ohms?		 If Yes, Replace wire    
  If No, Take SRS unit off of steering wheel and pull off plug.   Connect wires of SRS test plug 62 1260 and
measure resistance on disconnected plug with two test points.      1.4 to 1.8 ohms?		 If Yes, Replace SRS unit    
  If No, Replace contact ring.      
         
H or G Insulation of power supply wire to SRS unit against ground or against positive insufficient. Visual inspection of wires and plugs for cracks, dirt and moisture, replacing if necessary.    
K or J Insulation of power supply wire to left sensor against ground or against positive insufficient. Visual inspection of wires and plugs for cracks, dirt. (salt film) and moisture, replacing if necessary. or break in wire (J and L only).  Disconnect 4 pin plug on diagnosis unit and measure wire resistance.  9.5 to 10.5 k-ohms? If Yes, Replace diagnosis unit
      If No, Disconnect front sensor and measure resistance of front sensor.   9.5 to 10.5 k-ohms? If Yes, Replace wire.
      If No, Replace Front Sensor.  
M or L Right Sensor - See K or J above.      
O Insufficient ground connection between sensors or diagnosis unit and body.  Visual inspection of mounting parts and plugs for corrosion, replacing if necessary.    
N and H and K Left front sensor closed. Replace left front sensor.    
N and H and M Right front sensor closed. Replace right front sensor.    
N and V and K See K      
N and V and M See M      
Q/P/S/R/U/T/W/Y/X Defect in diagnosis unit. Replace diagnosis unit.