Mercedes-Benz Forum banner

ASR issue resolved!

29K views 18 replies 12 participants last post by  mattweisensee 
#1 ·
Well, its taken me 2 years of research but today I solved the problem of my ASR light coming on!.

Some background. 2 years ago I took a corner too quickly in the wet, the ASR activated to correct the problem. All good for another 2mins before the ASR light came on and stayed on. No other issue, just the light.

Since then, whenever the car was started, it would go through normal checks and always after 2 mins the light would come back on; regardless of whether the car moved or not.

analysis I did a lot of research on this site and others. Sensors were not the problem. I removed the ASR unit and tested the connectors for the resistance of each sensor (see in my other posts on this topic the ohms you should see). They were all good. Very unlikely that the sensors (after all they are just coils of wire) will go faulty.

I swapped out the ASR computer, again not the issue.

With a mate we reread the codes on the OBD and this is where I made the first mistake; mine is a 93 SL500 (in Australia) the same as a 94 in USA. I had interpreted the wrong code for pin 6 on the OBD. I had analysed it as a 95 model, not a 93.

So pin 6 error 21 tells of the ASR charge pump being faulty for a 92-93 model. This is where the problem lays; we had not interpreted the code correctly, looking at sensors instead of the charge pump.

Attached the picture of the ASR pump. It is mounted behind the front wheel arch splash guards. In summary now, the ASR charge pump had seized. It was not a problem with water or contaminates, simply age and two different metals working together.

We removed the pump and saw it had not worked for a long time. In my opinion the ASR light had not come on until I activated the ABS unit for skid control because up until then it had maintained adequate pressure with brake fluid.

After the pump was out we pulled the top off the electric motor, separating the pump from the commutator shaft. Cleaned it up, then reassembled.

Fixed after 2 years! at zero cost.

So the important things.

ASR light coming on without the car moving could well speak to ASR charge pump, certainly not sensors.

I subscribed to all data where I sourced the detailed circuit diagrams that helped me identify that the light was activated by a pressure switch in the ABS unit that was operated to OFF after the pump had actually charged.

The ASR pump is a very simple device and likely repaired with TLC , not requiring replacement.

I am a very happy man today ! No problems with my car( at least until the next one). Happy to share what I know about ASR lights!
 

Attachments

See less See more
1
#2 ·
Glad that you have managed to solve the problem.
Did the car go into "Limp Home Mode" when the ASR light came on?

Sort of on topic, I bought a pattern part brake light switch but when fitted the ASR light is permanently lit. I've just bought a genuine MB switch which I'm shortly going to install, so interesting if the ASR light goes out.
 
#6 ·
ASR

Just this week, on consecutive days and just after I pulled out of a junction to turn left and right my ASR light came on and "limp home" mode cut in, quickly switched off the ignition and then back on and it was ok, but will have to start checking things to get to the bottom of it. I have been in touch with the PO who had the ETA rebuilt with a new pot., and he had also changed(with a secondhand unit)the pump behind the splash guard in the wing. I will let you know how it all goes.:)
 
#7 ·
Just after the right codes




Hi,

I also have a 1993 SL in Australia. I purchased this car a few days ago with some known issues. I also have exactly the same symptoms as you mentioned above. I was a little confused about your code table comments? do you have the correct table for use on this car? or able to point me in the right direction?

Thanks in advance,

Lutz
 
#8 ·
Hi Lutz, hope this helps you, page 56 of the code manual should relate to your problem. If you are getting a code 24 that is charge pump. You should be able to hear the pump spin breifly when the ignition is turned on.
 

Attachments

#11 ·
Pump location different

I have been having exactly the same symptoms described here in post #1. I looked three different times under the fender well cover and could not find the ASR pressure pump. I finally started tracing lines off the ABS unit and found my pump attached below the brake master cylinder under the hood. Mine is a MY 94 SL made in 6-93. I took the pump apart and cleaned it as described and now my ASR has started working. Just though I would let people know of an alternate location to look.
 
#13 ·
Alternate location for ASR

I have been having exactly the same symptoms described here in post #1. I looked three different times under the fender well cover and could not find the ASR pressure pump. I finally started tracing lines off the ABS unit and found my pump attached below the brake master cylinder under the hood. Mine is a MY 94 SL made in 6-93. I took the pump apart and cleaned it as described and now my ASR has started working. Just though I would let people know of an alternate location to look.
Just looked there, Mine might be in the same spot, how do you remove it?

Thanks,
Lutz
 
#14 ·
Lutz, it is not under much pressure; 8 pis i recall when charged but it its not working probable none. Take the pipe that feeds from the bake booster first, but be ready to plug it or cap it so that you dont lose brake fluid , gravity will run it out. The pump is mounted on a bracket, easily removed , it is actually held in place by a rubber mount. Mine was behind the inside fender lining on the drivers side. *which is under the Booster. earlier in my thread I had a pic of it
 
#19 ·
Well, its taken me 2 years of research but today I solved the problem of my ASR light coming on!. Some background. 2 years ago I took a corner too quickly in the wet, the ASR activated to correct the problem. All good for another 2mins before the ASR light came on and stayed on. No other issue, just the light. Since then, whenever the car was started, it would go through normal checks and always after 2 mins the light would come back on; regardless of whether the car moved or not. analysis I did a lot of research on this site and others. Sensors were not the problem. I removed the ASR unit and tested the connectors for the resistance of each sensor (see in my other posts on this topic the ohms you should see). They were all good. Very unlikely that the sensors (after all they are just coils of wire) will go faulty. I swapped out the ASR computer, again not the issue. With a mate we reread the codes on the OBD and this is where I made the first mistake; mine is a 93 SL500 (in Australia) the same as a 94 in USA. I had interpreted the wrong code for pin 6 on the OBD. I had analysed it as a 95 model, not a 93. So pin 6 error 21 tells of the ASR charge pump being faulty for a 92-93 model. This is where the problem lays; we had not interpreted the code correctly, looking at sensors instead of the charge pump. Attached the picture of the ASR pump. It is mounted behind the front wheel arch splash guards. In summary now, the ASR charge pump had seized. It was not a problem with water or contaminates, simply age and two different metals working together. We removed the pump and saw it had not worked for a long time. In my opinion the ASR light had not come on until I activated the ABS unit for skid control because up until then it had maintained adequate pressure with brake fluid. After the pump was out we pulled the top off the electric motor, separating the pump from the commutator shaft. Cleaned it up, then reassembled. Fixed after 2 years! at zero cost. So the important things. ASR light coming on without the car moving could well speak to ASR charge pump, certainly not sensors. I subscribed to all data where I sourced the detailed circuit diagrams that helped me identify that the light was activated by a pressure switch in the ABS unit that was operated to OFF after the pump had actually charged. The ASR pump is a very simple device and likely repaired with TLC , not requiring replacement. I am a very happy man today ! No problems with my car( at least until the next one). Happy to share what I know about ASR lights!
I just bought a US model 1995 SL and the ARR light comes on after a couple of minutes. can you provide me with some short cuts on how to remove and reassemble the pump? matt
Lutz, it is not under much pressure; 8 pis i recall when charged but it its not working probable none. Take the pipe that feeds from the bake booster first, but be ready to plug it or cap it so that you dont lose brake fluid , gravity will run it out. The pump is mounted on a bracket, easily removed , it is actually held in place by a rubber mount. Mine was behind the inside fender lining on the drivers side. *which is under the Booster. earlier in my thread I had a pic of it
Driver’s Side? Which country? I’m in US. Left side driver.
 
#16 ·
Thanks KA 707,

My wifes '90 SL500 has the exact same problem. The ASR light comes on after exactly 2 minutes after starting the car. I have timed it for months while trying to determine what that might mean. As it turns out the system is designed to inhibit the ASR light from illuminating for 2 minutes after start if the accumulator (pressure holding tank) is not charged up to full system pressure. When the car is started, if the accumulator pressure is low, the pump begins to pressurize the accumulator. A pressure switch shuts off the pump when proper pressure is reached. If the ASR system uses some of the stored pressure or it leaks down the pump will turn on again to keep the pressure up.

If for any reason the accumulator does not reach full operating pressure within 2 minutes, the system then turns on the ASR light.

I have the Mercedes WIS program with all of the maintenance and parts manuals but even after months of research, I could not find ant reference in the manual to the 2 minute inhibit of the ASR light illumination. When I read your post, it confirmed my suspicions about a low pressure situation in the accumulator.

BTW- On the 1990 SL500, the pump is bolted on underneath the brake master cylinder

Thanks for your post!!
 
#17 ·
Hi all.
I have an R129 500 SL in white with 79k miles.
It does this ASR/ABS thing. Sometimes when I start it and sometimes while driving.
It then seems to become lumpy and over rev, also causes the engine temp gauge to rise ( I don't know if the actual engine reaches those temps or if its just gauge going mad)
I'm not techy at all with cars so no chance of me being able to take asr out and diagnose.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top