Error Code Reader and Reset Tool - (incomplete - 10/1/02)

Overview

On my 1989 560 SEC (non-Cal) I have a problem with my SRS light constantly on.  I searched the MBCoupes archives and found an entry by Randy D. (See Below).  Randy, explains how to read the codes at Pin-6 of the X92 connector and want the codes mean.  He states that the tool that was used to read the codes was simply an LED and to clear the codes you must bridge pins 1-6.   From this description I put together a simple tool for a couple of bucks that reads out the error codes and allows you to reset them.  The tools is simply an LED, a push button switch (normally open) and a pair of banana plugs (red/black).

Required Parts

1 - 12v LED assembly (Radio Shack# 276-270)
1pair - Banana Plugs (red/black) (Radio Shack# 474-721C)
1 - Push Button Normally Open (Radio Shack)
22 gauge wire, solder, tie wraps, heat-shrink tubing, solder iron (all avail at RS)

Disclaimer

The following procedure was done on my 1989 560 SEC and I can't say if this procedure will apply to other years and/or models.  This procedure worked for me and anyone else should use this writeup only as a reference.  
ALSO VERY IMPORTANT, the SRS system is a very complicated and potentially dangerous system for DYI 'r to be working on and should be maintained by qualified MB technicians.

Assembly

This tool is rather simple to assemble and requires very basic soldering skills.  See electrical diagram in Fig-1.  The parts required for the tool were available at Radio Shack.  It's important to note that the LED has to be able to handle 12VDC, RS has panel mount LED assy that operates on 12v that worked nicely.  If you're unable to find this part and you're using a regular LED, you'll have to add a resistor in series with that LED, since LED's normally work on 2-3VCD and would probably pop at 12v.

  1. Simply solder two 4 inch lengths of 22 gauge insolated wire to the normally open leg and common leg of a push button switch.
  2. Slide heat shrink over the bare legs of the switch and heat.  The slide a larger piece of shrink over the button portion of the switch, the legs and wire, then shrink.  This is just to keep any from shorting out while in use and to help protect the connections.  If heat shrink isn't available, use electrical tape.
  3. Strip back a 1/4 inch of insulation from the ends of the 2 LED leads and the 2 switch leads.
  4. Twist bare ends of the black LED lead and the common switch lead together and insert into the Black banana plug as per the plug directions.   (For the plugs I used, unscrew the plastic end and slide over the wire.  Unscrew the metal ring from the end of the plug, insert wire, pull bare end through hole, bend wire over and screw metal ring back on.  Now the wire is attached to the plug, then screw plastic end back on.)
  5. Repeat step-4 with the red lead and the normally open lead of the switch and the red banana plug.
  6. Tie wrap the wires and LED assy as seen in Fig-2.  To make a neat job of it..

Operation - SRS

The black plug gets plugged into connector #1 of the X92 connected and (to test SRS) the red plug gets plugged into connector #6 of X92.  Using my tool I followed Randy's procedure to diagnose my problem as follows. 

  1. With the ignition key on in #1 position and the SRS Indicator constantly lit, the LED was rapidly flashing.
  2. I pressed the push button for a 2 seconds and released, the LED came on for a second and then flashed 3 times at slower rate. Then went back to rapid flashing.  This indicated (according to Randy's chart) that the Driver air bag (slip rings or brushes) was a problem.
  3. I repeated step 2 and it flashed 8 times. This indicated that there was Voltage supply problem.
  4. I repeated step 2 again and it flashed 10 times - Control Unit has been activated. (This one sounds like bad news.)
  5. I repeated step 2 and it went back to 3 flashes.  So there was a total of 3 problems stored in my SRS memory.  Not knowing when these errors were stored I decided to erase them and see if they would come back.  Here again, I followed Randy's procedure.
  6. I went back to step-2 to read the first code, immediately after the 3 flashes I held the button for 6 seconds to clear the stored code.  Then repeated this procedure for the remaining 2 stored codes.  When I was done codes 3 and 8 were erased, but as Randy stated, 10 would not erase.  (I guess that means I got to go to MB).

Operation - CIS-E (not complete)

This tester can also be used to read/reset the errors code from the fuel injection system's CIS controller similar to the SRS system.  The black plug gets plugged into connector #1 of the X92 connected and (to test CIS) the red plug gets plugged into connector #3 of X92. Fault code table.

Operation - Automatic Climate Control (not complete)

This tester can also be used to read/reset the errors code from the Automatic Climate Control System similar to the SRS system.  The black plug gets plugged into connector #1 of the X92 connected and (to test Auto-Climate System) the red plug gets plugged into connector #7 of X92.

 


Fig-1


Fig-2                                                                         Fig-3


Fig-4

Reading SRS Codes (copied from MBCoupes archive, email sent by Randy D.)                             
 Hi Wes,
   You have to clear the codes to make the light go out. Once the system stores a code, the light stays on. I think I tried to explain this a long time ago, but on that model you can access the codes and clear them without the special tool. When the first "self-diagnosing" system came out, they gave us an LED to use for diagnosis. It was a very nice unit made by Hirschmann with two pins of the correct diameter and holes for a jumper wire. The LED is
connected between terminals #1 and #6 on the diagnostic connector (black plastic piece near the battery on 124 and 126 cars).
To access codes the terminals are bridged for "AT LEAST TWO SECONDS, BUT NOT MORE THAN FOUR". Then you repeat the process for remaining codes. If the code repeats there is only one stored. Otherwise they start repeating again when you've read all
of them. The various faults reveal themselves as "blinks" as follows:
             1) No codes stored
             2) Control unit
             3) Driver air bag (slip rings or brushes)
             4) not used
             5) Driver set belt buckle
             6) Passenger seat belt buckle
             7) not used
             8) Voltage supply
             9) Warning lamp defective
            10) Control unit has been activated-The only code that can't be erased.
             (#10 can occur even if the air bag didn't go off under certain conditions)
   To erase the codes, with the fault displayed...wait two seconds, then the terminals (#1 and #6) must be bridged for "AT LEAST SIX SECONDS, BUT NO MORE THAN EIGHT SECONDS". Each code must be erased individually. When you're done, go back and check again for codes...it should read "1" blink.
  Regards,
   Randy D.

 

CIS-E Fault detection Table (Cal?)
Flashes  Fault
  1.      No fault in System
  2.      Throttle valve switch, full throttle contact
  3.      Coolant temperature sensor
  4.      Air flow sensor potentiometer
  5.      O2 Sensor
  6.      Not assigned
  7.      TD Signal
  8.     Altitude correction sensor
  9.     Electrohydraulic actuator (EHA)
  10.     Throttle valve switch, Idle contact
  11.     Not assigned
  12.     Exhaust gas recirculation