Like many 1991 Mercedes Benz 500sl owners, I’ve been increasingly frustrated by the dreaded SRS light illuminating on my dashboard. This issue was often accompanied by the car entering limp home mode, significantly reducing performance and driving enjoyment. Initially, it was an infrequent occurrence, but over the last year, it escalated to happening daily, sometimes multiple times. Knowing this is a well-documented problem within the 500SL community, I began researching potential causes and solutions.
Forum discussions and online resources pointed towards the Electronic Throttle Actuators as the most likely culprit for this issue in the 1991 Mercedes Benz 500SL. The cost of replacing these actuators is substantial, prompting me to consider a DIY approach. My plan is to eventually remove and inspect them, following guides like the one at v12uberalles.com, to check if rewiring is needed due to insulation breakdown. However, this is a time-consuming project that would leave my 500SL out of commission for a while. I considered a slightly less invasive rewiring method using heat shrink tubing over the existing wires, requiring only unsoldering one end, as cutting open the plug seemed overly complex.
Seeking a quicker, interim solution to get my 1991 Mercedes Benz 500SL back on the road reliably, I decided to temporarily disable the Automatic Slip Regulation (ASR) system. Drawing inspiration from another forum member’s post about installing a RENNTech ASR defeat switch, I opted for a simpler approach. This involved carefully cutting three specific wires in the wiring loom leading to the ASR (and ABS) computer. After pulling back the insulation to access the wires, I identified the blue/white, brown/blue, and brown/yellow wires mentioned in the RENNTech switch installation guides.
Since performing this modification, my 1991 Mercedes Benz 500SL now drives beautifully, and the limp home mode issue has vanished. To address the permanently illuminated ASR dash light, I simply removed the bulb. The snow traction control switch’s red LED is now constantly lit, but this is a minor visual inconvenience I am willing to accept.
In my driving experience, the traction control in the 500SL rarely engaged, even prior to disabling the ASR. Living in Australia, where snow and ice are nonexistent, traction control isn’t a necessity for my driving conditions. Furthermore, I’ve driven high-performance cars without traction control in the past and am comfortable doing so. I even previously installed a first-gear start device in my 500SL, which inherently increases the potential for wheel spin.
My primary motivation for sharing this experience is to potentially assist other 1991 Mercedes Benz 500SL owners facing similar SRS/limp mode problems. Beyond this, I am curious to know if disabling the ASR system in a 500SL results in any performance gains, such as increased power. Are there any other advantages to installing a proper ASR defeat switch beyond simply resolving the SRS/limp mode issue temporarily? Any insights or experiences from other 500SL enthusiasts would be greatly appreciated.
