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Amedee, Mercedes Technician
Category: Mercedes
Satisfied Customers: 26645
Experience:  ASE certified Technician advanced level specialist
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91 SL 500 has persisting ABS ASL warning lights..electrical fault

Resolved Question:

91 SL 500 has persisting ABS ASL warning lights after an electrical fault has been repaired. Power down to 2/3. How can this be corrected?
Submitted: 8 years ago.
Category: Mercedes
Expert:  Amedee replied 8 years ago.

Hello there!


Acceleration Slip Regulation (ASR) light is on with fault code 13.




1. Test fuse #5 in front fuse panel.

2. Locate stop lamp switch. Test for key on battery voltage at Red/Blue wire with brake pedal not pressed. Press brake pedal and voltage should drop to less than one volt.

3. Test voltage at Black/Red wire, key on battery voltage with pedal pressed. With pedal not pressed, voltage should drop to less than one volt.

Potential Causes:

Stop Lamp Switch
Stop Lamp Switch Wiring


Customer: replied 8 years ago.
Also ASD light is on and power is down to 2/3 normal. I will have the opportunity to check your reply in the next 36 hours.
Customer: replied 8 years ago.
Also ASD light is on and power is down to 2/3 normal. I will have the opportunity to check your reply in the next 36 hours.
Expert:  Amedee replied 8 years ago.

THe ASD lights stands for the Automatic locking differential.


Description and Operation


The automatic locking differential (ASD) engages the differential lock only when needed, and is electronically controlled. A function indicator lamp, located in the speedometer shows engagement.
Signals from the speed sensors are relayed to the ASD control unit which processes an average speed of the front and rear wheels. The control unit uses this information to send a signal to the solenoid valve in the hydraulic unit. The hydraulic oil is stored under pressure and then within fractions of a second is sent from the pressure reservoir to the differential housing at the rear axle. The hydraulic clamping force of the multi-disc clutch locks together the differential rotation between the rear wheels. This lockup transfers the road torque lost by the slipping wheel to the wheel with traction.


The light is on because you have a code in the computer.


Reading Diagnostic codes in the computer using the Warning Lamp


Start engine.
Using suitable jumper wire, connect diagnostic test connector terminals 1 and 5 for about 1 second.
Remove wire, warning lamp goes out for about 2 seconds, then flashes at 1 second intervals.
The number of blinks indicates the malfunction code.
Malfunction codes are as follows:
Code 1: No malfunction.
Code 2: ASD control unit faulty.
Code 3: Stop lamp switch, ASD engagement function faulty.
Code 4: No left front wheel speed sensor.
Code 5: No right front wheel speed sensor.
Code 6: No rear axle speed sensor.
Code 7: No wheel speed signal from any sensor.
Code 8: ASD value or stop lamp switch engagement faulty.

Customer: replied 8 years ago.
I am sorry. I am asking the wrong questions -the 2 warning lights on are the ASR & ABS. The power seems reduced and the electric hood does not operaate - sorry for the incorrect info,
David C
Expert:  Amedee replied 8 years ago.



NO problem!


The ASR light stands for Acceleration Slip Regulation and the ABS light obviously is for the Anti lock brake system.


The reason for these lights coming on is because you have a code in the ABS system. You will need to get your ABS computer scanned for codes and fix the area of concern.


Unfortunately, you will need to go to a shop that has a scanner that can pull codes from your ABS system. There is no way to pull codes from the ABS system without the use of a scan tool.


THe diagnostic procedure and a list of the codes are listed below.


Displaying & Reading Trouble Codes (DTC Memory)


Traction Systems (ABS, ASR, ETS) and Speed-Sensitive Power Steering (SPS)

Models 129, 140 as of 06/94 up to 08/95 (ASR, ETS, SPS)

Preparation for DTC Readout


Connect impulse counter scan tool or Hand-Held Tester (HHT) to data link connector (X11/4) according to connection diagram.


Connect yellow wire from impulse counter scan tool to:
ASR/SPS or ETS/SPS control module (N47-1 N47-2): socket 6
EA/CC/ISC control module (N4/1): socket 7
Base module (N16/1): socket 8
Engine control module (N3/4): socket 4
LH-SFI or right LH-SFI control module (N3/1, N3/3): socket 4
Left LH-SFI control module (N3/2): socket 5
DI or right DI control module (N1/3, N1/5): socket 17
Left DI control module (N1/4): socket 18


Ignition: ON
Read out DTC memory for control modules.






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