Experiencing the dreaded SRS light illuminating on your dashboard, followed by your 1991 Mercedes Benz 500sl entering limp home mode, is a common and frustrating issue for owners of this classic roadster. Many enthusiasts in online forums have discussed this problem extensively, and if you’re facing this situation, you’re certainly not alone.
The primary culprit often pointed to for this issue is the Electronic Throttle Actuator (ETA). Replacing these units can be a significant expense, prompting many owners to explore more cost-effective solutions. One such approach involves inspecting and potentially rewiring the ETAs themselves, a process detailed on websites like v12uberalles.com for those technically inclined and willing to undertake a DIY repair. This is a time-consuming task that will render your 1991 Mercedes Benz 500SL undrivable for a period. The wiring within the ETA is known to degrade over time, with the insulation around the wires becoming brittle and failing. A meticulous rewiring job can potentially restore functionality.
However, for those seeking a quicker, albeit temporary, solution to get their 1991 Mercedes Benz 500SL back on the road, disabling the Automatic Slip Regulation (ASR) system can sometimes provide immediate relief. This involves interrupting the ASR system by cutting specific wires in the wiring loom leading to the ASR (and ABS) computer. This method, inspired by aftermarket ASR defeat switch installations like those from RENNTech, effectively bypasses the ASR system. In a 1991 Mercedes Benz 500SL, the wires typically involved are blue/white, brown/blue, and brown/yellow.
By disconnecting these wires, drivers have reported their 1991 Mercedes Benz 500SL returning to normal driving operation, resolving the limp mode issue and allowing for regular use of the vehicle. While the ASR warning light on the dash will likely remain illuminated (and can be addressed by removing the bulb), and the snow traction control switch LED may stay on, the car becomes drivable.
It’s important to understand that disabling ASR is not a permanent fix for the underlying issue, which is often related to the Electronic Throttle Actuators. Traction control in these older 1991 Mercedes Benz 500SL models was less sophisticated than modern systems, and for drivers accustomed to older, high-performance vehicles without such aids, the absence of ASR in dry conditions may not be significantly missed. Particularly in regions without snow or ice, the system might not frequently engage under normal driving conditions. Some owners even find that disabling ASR, especially when combined with modifications like a first-gear start device (which makes wheelspin easier), offers a more direct and engaging driving experience in dry conditions.
While this ASR disable method can be a helpful temporary workaround, it’s crucial to remember that it does not address the root cause of the SRS/limp mode problem in your 1991 Mercedes Benz 500SL. Further investigation into the condition of the Electronic Throttle Actuators and their wiring is recommended for a long-term, reliable solution. Consulting with a Mercedes-Benz specialist is always advisable for diagnosing and properly repairing these complex systems.
