The Anti-Theft Alarm (ATA) system in your classic Mercedes SL 500 is an intricate part of its overall vehicle electronics. If you’re experiencing issues with your SL 500’s alarm, you might be looking for ways to diagnose the problem yourself. While simply disconnecting the ATA module might seem like a quick fix, it’s often not that straightforward due to its integration with the starter relay and other crucial systems. For owners of early models, a DIY scan tool can be a valuable asset in understanding and potentially resolving alarm system faults. This guide focuses on helping you understand the ATA system in your early model Mercedes SL 500 and how to read fault codes using a simple tool.
For Mercedes SL 500 models from the early 1990s, the 16-pin diagnostic connector is your gateway to accessing the ATA system’s error codes. Typically located under a small cover near the strut mount on the right side of the engine compartment, this connector allows you to interface with the car’s diagnostic system. The ATA control module itself is usually found in the trunk, on the upper right side.
To retrieve fault codes from your Mercedes SL 500’s ATA system, you can utilize a basic DIY scan tool. This tool, in its simplest form, is essentially a push-button switch and an LED light wired together. By momentarily grounding pin 11 of the 16-pin diagnostic connector, you can initiate the fault code readout. The codes are displayed as blinks on the LED, with one blink indicating no errors. To clear a detected error code, you would typically close the switch for a duration of 4 to 8 seconds.
Here’s a breakdown of the ATA fault codes for your early Mercedes SL 500:
ATA Fault Code Table (Blinks)
| Fault Code (Blinks) | DTC Readout | Possible Cause of Failure |
|---|---|---|
| 1 | No fault found | |
| 2 | Alarm activated, trunk sensor circuit | Trunk sensor malfunction or circuit issue |
| 3 | Alarm activated, engine hood circuit | Hood sensor malfunction or circuit issue |
| 4 | Alarm triggered, glove compartment | Glove compartment sensor or circuit problem |
| 5 | Alarm activated, rear circuit Console compartment circuit | Rear or console compartment sensor/circuit issue |
| 6 | Alarm activated, front door circuit | Front door sensor malfunction or circuit issue |
| 10 | Alarm activated, radio circuit | Radio theft alarm trigger or circuit issue |
| 12 | Alarm activated, ignition circuit | Ignition system alarm trigger or circuit issue |
| 14 | Alarm activated, brake circuit | Brake system alarm trigger or circuit issue |
| 19 | AT Control module faulty | ATA control module malfunction |
| 20 | Left front door actuator, No ground connection | Door actuator grounding issue |
| 21 | ATA disarmed, Starter lock-out relay module. short to circuit 30 | Starter lock-out relay or circuit short |
| 23 | ATA armed, Open to circuit 30 | Circuit 30 open circuit issue |
Alt: Location of the 16-pin diagnostic connector in a Mercedes SL 500 engine bay, used for reading anti-theft alarm codes.
To construct the scan tool for your Mercedes SL 500, you’ll need an LED, a 1k resistor, a push-button switch, and some wires. The wiring diagram is as follows:
0_______/ ______0_______LED_______/\/\/\/\______0
12V+ pin 1 SW pin 11 C A 1K resistor pin 16Connect the scanner wires to the 16-pin Data Link Connector as indicated:
- Socket 11 (switch): Black wire
- Socket 1 (-) ground: Red wire
- Battery (+) (LED): Red wire (also connected to resistor)
Alt: Wiring diagram for a DIY scan tool used to diagnose the Anti-Theft Alarm system on early Mercedes SL 500 models.
It’s important to note that this DIY scan tool method is primarily applicable to early Mercedes SL 500 models equipped with the 16-pin diagnostic connector. Later models feature more advanced systems that require sophisticated computer scanners for diagnosis. If you find this process technically challenging or are uncomfortable working with your vehicle’s electronics, it’s always recommended to seek assistance from a qualified Mercedes-Benz repair professional. They possess the expertise and tools necessary to accurately diagnose and repair your SL 500’s anti-theft alarm system.
