1991 500SL ASR light, disable traction control

[allanb888]

Over the last year I have experienced increasing frequency of the SRS light coming on in my 1991 500SL, and then the car going into limp home mode. Eventually it started happening every day, sometimes a few times a day.

I know this dreaded problem has been discussed many times before in this forum.

The cost of replacement of the Electronic Throttle Actuators, which are the most likely cause of the problem from forum posts, is very high, and I intend to eventually remove them to check if they need rewiring as detailed at
http://v12uberalles.com/throttle_actuator_rewire.htm . This would take quite a bit of time, and would disable the car for a while. Actually I thought that because complete rewiring would require that the plug be cut open, which is fiddly, I would use heat shrink over the existing wires, only requiring unsoldering one end. Apparently the problem is because the insulation around the wires breaks down.

In the meantime, as a quick solution, I disabled the ASR by cutting 3 wires in the wiring loom just before it plugs into the ASR (and ABS) computer, after pulling back the insulation. I got the idea from another member's post about installing the RENNTech ASR defeat switch. The switch is installed by cutting the same wires, and flicking the switch, connects and disconnects the wires as required. In my car they were blue/white, brown/blue, and brown/yellow wires.

My car now drives very nicely, and I removed the ASR dash light globe, since it was on permanently. The snow traction control switch red LED light is on , but I can live with that.

Previously the traction control rarely came on when I was driving, and I do not miss it at all. Where I live in Australia there is no ice or snow, and I suppose I previously got used to driving high performance cars before the introduction of traction control. By the way, I previously installed a first gear start device, which would make it easier to spin the back wheels.

I firstly wanted to share my experiences in case it can help someone else.
Secondly, does any one know if you get more power in a 500SL by switching off the ASR? Any other advantages in installing an ASR defeat switch?

[Dale93500SL]

Sounds like you have the exact problem I do, would like to try the same fix you talk about. But not sure where the wires are also does your car idol and accelerate correctly? The site you mention that discribes the indepth fix talks about the car learning idol and full throttle again after the wire fix. I pasted your post on this e-mail will try it after you reply. Thanks you made my day with your recommendation to cut the wires.

Dale
Corpus Christi, Texas USA


In the meantime, as a quick solution, I disabled the ASR by cutting 3 wires in the wiring loom just before it plugs into the ASR (and ABS) computer, after pulling back the insulation. I got the idea from another member's post about installing the RENNTech ASR defeat switch. The switch is installed by cutting the same wires, and flicking the switch, connects and disconnects the wires as required. In my car they were blue/white, brown/blue, and brown/yellow wires.

[bobterry99]

Alan, I think you meant to cut the brown/red wire instead of the brown/yellow. The /red wire goes to the ASR malfunction indicator lamp in the cluster and the /yellow goes to the ABS MIL. Of course, with the ASR MIL removed from your cluster there is no point in cutting the /red wire now.

The typical symptom of an electronic throttle actuator (ETA) that is going bad is a faulty feedback signal to its control module. The ETA control module requires this signal, and when it is faulty the module turns-off the ETA and enters Limp Mode. The ASR controller recognizes this condition and turns-on the ASR MIL. In this instance defeating ASR will not restore the car to normal operation and leave Limp Mode.

[Dale93500SL]

Bob,
If what I think your saying then cutting the wires will do nothing, you already have this situation with bad wires you get no signal? Then you have accomplished nothing......

[bobterry99]

I think a little technical background might help. The electronic throttle consists basically of an accelerator position sensor (potentiometer), a control unit, and a throttle actuator (ETA) -- a motor that moves the throttle valve. This system is seperate from the ABS/ASR system, though the two communicate.

The ETA reports its position to the controller. While the ignition is on the throttle control unit monitors the quality of that signal and the quality of the signal it receives from the accelerator position sensor. If it detects a problem in either, then it will switch-off the ETA and cause the car to go to Limp Mode.

From the above description you may see that a failing ETA is an electronic throttle problem basically not related to ASR. It may appear to the driver that it is an ASR problem, because when the ETA switches-off the ASR recognizes the problem and turns-on its MIL.

So, disabling ASR will not cure Limp Mode in the case of a bad ETA, but it may improve performance under other circumstances. The ASR controller can signal the throttle controller to override the driver and reduce the opening of the throttle when it detects wheel-spin. A malfunction in the ASR could cause it to signal throttle rduction inappropriately, and in this case disabling ASR would be beneficial.

[allanb888]

Originally Posted by bobterry99

I think a little technical background might help. The electronic throttle consists basically of an accelerator position sensor (potentiometer), a control unit, and a throttle actuator (ETA) -- a motor that moves the throttle valve. This system is seperate from the ABS/ASR system, though the two communicate.

The ETA reports its position to the controller. While the ignition is on the throttle control unit monitors the quality of that signal and the quality of the signal it receives from the accelerator position sensor. If it detects a problem in either, then it will switch-off the ETA and cause the car to go to Limp Mode.

From the above description you may see that a failing ETA is an electronic throttle problem basically not related to ASR. It may appear to the driver that it is an ASR problem, because when the ETA switches-off the ASR recognizes the problem and turns-on its MIL.

So, disabling ASR will not cure Limp Mode in the case of a bad ETA, but it may improve performance under other circumstances. The ASR controller can signal the throttle controller to override the driver and reduce the opening of the throttle when it detects wheel-spin. A malfunction in the ASR could cause it to signal throttle rduction inappropriately, and in this case disabling ASR would be beneficial.

********************************************************
I understand what you are saying, and I don't know exactly what circuits are disabled by cutting the wires I mentioned, but definitely limp home mode has not come on since I made the cut, and the car drives beautifully.

I knew that I was taking a bit of a gamble not knowing for sure that my wires were the same colours as other cars around the world, but I reasoned that I could always resolder the wires if I needed to, and it was an easily accessible
area.

[allanb888]

Originally Posted by bobterry99

Alan, I think you meant to cut the brown/red wire instead of the brown/yellow. The /red wire goes to the ASR malfunction indicator lamp in the cluster and the /yellow goes to the ABS MIL. Of course, with the ASR MIL removed from your cluster there is no point in cutting the /red wire now.

The typical symptom of an electronic throttle actuator (ETA) that is going bad is a faulty feedback signal to its control module. The ETA control module requires this signal, and when it is faulty the module turns-off the ETA and enters Limp Mode. The ASR controller recognizes this condition and turns-on the ASR MIL. In this instance defeating ASR will not restore the car to normal operation and leave Limp Mode.

************************************************************
I double checked the wires I cut, and they are the colours I mentioned. I also checked the article about the Renntech ASR bypass switch, and they also give the same wire colours (left hand drive car). The article gave a copy of Renntech's instructions, which were not model specific. I did not cut the brown/red wire which goes to the ASR warning light, which came on permanently, and that's why I removed the globe. After reading your post I checked if my ABS light and system still works, and it does.

It worked on my 1991 car, which is right hand drive, but I do not know if all years have the same wire colours. There may also be differences between countries.

You obviously have access to a technical manual and wiring diagrams. Which year and model is it for?

Allan

[allanb888]

Originally Posted by Dale93500SL

Sounds like you have the exact problem I do, would like to try the same fix you talk about. But not sure where the wires are also does your car idol and accelerate correctly? The site you mention that discribes the indepth fix talks about the car learning idol and full throttle again after the wire fix. I pasted your post on this e-mail will try it after you reply. Thanks you made my day with your recommendation to cut the wires.

Dale
Corpus Christi, Texas USA


In the meantime, as a quick solution, I disabled the ASR by cutting 3 wires in the wiring loom just before it plugs into the ASR (and ABS) computer, after pulling back the insulation. I got the idea from another member's post about installing the RENNTech ASR defeat switch. The switch is installed by cutting the same wires, and flicking the switch, connects and disconnects the wires as required. In my car they were blue/white, brown/blue, and brown/yellow wires.

***********************************************************

I disabled the ASR on my daily car about 10 days ago, and it drives perfectly in every way including idle and acceleration.

The ASR (and ABS) computer is in a plastic box with many other computers, under the hood, in front of the passenger windscreen. The lid is held by 5 small bolts. I have a right hand drive car (Australia), but I looked at a dealers left hand drive parts manual, and it is in front of the passenger compartment also. Maybe another forum member can post a diagram of the computer compartment layout, so you can identify the correct computer. Disconnect the one plug that attaches to the computer, and pull back the insulation without tearing it. Identify the coloured wires I described from about 20 wires. I cut the 3 wires about 4 cms from the plug so there is enough length
to resolder them later if you want to. Then pull the insulation back in place and put everything back.

Allan

[Tyler_P360]

Had similar issues a while back, so much useful info here that could have helped me, thanks guys