Is this a crazy theory? SL600 - PeachParts Mercedes-Benz Forum

stsintx · #1 02-03-2006, 09:52 AM

On my 94 SL600, I get ASR light on sometimes,
This is how it goes in every couple of days, I start the car in the morning and hear ABS/ASR pump run for like 10 15 seconds, then shuts off. within couple of minutes it starts and shuts off again, this happens usually 3 to 4 time, and then ASR light comes on and pump doesnt start anymore. Each and everytime after this incident I get code 22 "Pressure switch leakage" from socket 6 (ABS/ASR control module).

I have replaced the brake fluid, and checked all the hydraulic lines and didnt find any leaks whatsoever. After replaceing the brake fluid it did help a little bit but not too much. I followed alldatadiy instructions and tested the Wiring that goes between the control module and ABS/ASR pump, everthing is in accordance with specified values. I have tested the Hydraulic system and pressure values are also satisfying. Last option is replacing the ABS/ASR pump to see if it makes a difference.

On the other hand, I felt that while this incident is happening, I feel the brake pedal gets slightly firmer like Brake booster is filled with air. Or when you turn the engine off brake pedal gets firmer, its almost like that, its not that firm but I can feel a little firmness. Also, while this incident is in progress it usually lasts 1 to 5 minutes, Engine idle is erratic, like there is a vacuum leak or something like that.

My theory is, I am guessing there is a valve or something which controls the vacuum system. when it malfunctions it causes an erratic idle and causes the brake booster fill with air. and when I apply brake pedal, system recognizes that there is not enough pressure and turns the ABS/ASR pump on to pressurize the system. However, after cycling couple of times system is still not pressurized enough, then the control module thinks there is a hydraulic leak somewhere and turns on ASR MIL light and turns off ABS/ASR pump.

Does this make any sense! does this theory at least sound logical?

Arthur Dalton · #2 02-03-2006, 11:07 AM

try bleeding the pump...there is a port there for such.

stsintx · #3 02-03-2006, 01:03 PM

I have bled the pump and even checked for the PSI and everything is in specified values.

#4 02-03-2006, 01:15 PM

the wiring harnesses on this model (and many other mercedes) are notorious problem causers. i have seen the harness on the 600 throttle actuators cause simmilar issues like you are having, i would suggest that you physically inspect all engine harnesses for heat damage. specifically the harnesses to each throttle actuator. cut them gently with a razor and look for damage inside. be warned however if these units are bad they can cost thousands each. also if they are defective cutting them open to inspect may compound your problems and not allow the car to be driven. you could start your inspection at the main engine harness if is damaged, you can usually bet the actuators and air mass meter harnesses are as well. all can be a very costly repair.

stsintx · #5 02-03-2006, 01:42 PM

Thanks for the advise Carson, however, ETA s are rebuilt by me, last month vehicle was in limp home and there was 20 different errors now they are all gone after rewiring, wire between the control module and ABS/ASR pump checked out ok I dont have any problems with wires at all, no cracks nothing at all and consistancy is pretty good.

I was thinking maybe the item number 101 in the picture below, has something to do with idle and pressure switch error.

#6 02-03-2006, 02:15 PM

Quote:

Originally Posted by stsintx

Thanks for the advise Carson, however, ETA s are rebuilt by me, last month vehicle was in limp home and there was 20 different errors now they are all gone after rewiring, wire between the control module and ABS/ASR pump checked out ok I dont have any problems with wires at all, no cracks nothing at all and consistancy is pretty good.

I was thinking maybe the item number 101 in the picture below, has something to do with idle and pressure switch error.

the booster hose? that sound probable, do you think it has a leak? or the valve is bad?

stsintx · #7 02-03-2006, 02:34 PM

I am guessing, either hose or the valve has a problem, because when ASR light comes on, brake pedal gets pretty stiff, like vacuum line is not sucking the air from booster and engine idle is erratic.

SD300 · #8 02-03-2006, 02:47 PM

Run a tee off the vac line, gently route her outside the hood and tied vac gauge to wiper blade, so u can see the vac when driving her.
Tee off where the vac line goes into the brake booster.

Hope that gave u more to check on.

stsintx · #9 02-03-2006, 03:00 PM

yeah, i should give this a try, it happens mostly mornings so I should hook it up and then start the car lets see. only problem is finding a tee that fits there.

Also I forgot to add, when I started the engine this morning, I heard the Pump running, it was going to give me that ASR light again, pump ran for 10 seconds and stopped. within 10 seconds It starrted running again, and I decided to higher the RPM and kept it around 2000rpm for like 15 seconds. Then pump stopped and didnt run again brake pedal became a little softer and ASR light didnt show up, so this is really directing me to a vacuum problem, what do you all think?

Arthur Dalton · #10 02-03-2006, 03:04 PM

Should be a check valve between the booster and the intake... I would try cleaning/replacing that first..

stsintx · #11 02-03-2006, 03:10 PM

I am guessing the check valve also,when i turn off the engine if its not holding the back pressure of the intake, It might fill up the brake booster with air, maybe thats why I am getting this stiff pedal in the mornings and after a while vacuum line sucks all the air and everything goes back to normal.

Arthur Dalton · #12 02-03-2006, 03:18 PM

They list a gasket for the vac fitting at the booster... might want to take a peak at that too............

stsintx · #13 02-03-2006, 05:33 PM

I pulled out the vacuum hose and cleaned it with carb cleaner and some degreaser, its a T shaped hose and it has two check valves on it, right bank check valve works fine but left cylinder bank was clogged a little bit tried to clean it, put it back on the car, in the morning I will start the car and see if there is any change.

Gasket seemed ok.

Gilly · #14 02-03-2006, 05:41 PM

Without a manual, little fuzzy on this, but here's something to consider: When the car is started cold, the AIR pump runs for maybe 2 minutes (kinda standard thing), then shuts off. A few minutes later, the pump should run again (for maybe 5 seconds or so) as the computer checks to see if the AIR pump works (looks at the O2 sensor). So given the symptoms, I wonder if something may be goofed up in either the wiring or vacuum pipe routing? There is also a divert valve involved which uses an electrical switch-over valve for the divert valve. Most of these things (vacuum piping and switchover valve wiring) can easily be plugged in to the wrong thing (switch over valves for the divert valve and EGR valve for example can be mixed up electrically and vacuum lines, other possiblities exist I'm sure)
Gilly

stsintx · #15 02-04-2006, 09:59 AM

Thanks for the advise gilly, this morning when engine was cold I started the car, heard both air and ABS/ASR pump run. ABS/ASR pump stopped after 10 seconds. Air pump kept running, after like 20 30 seconds I heard the ASR/ABS pump run again for another 5-7 seconds, then it stoped. I put the car in reverse and moved out of my garage as soon as brake pedal applied for a second I felt the pedal kicking like ABS system was active, I didnt mind and kept on driving, brake pedal feels a little firmer than yesterday, I guess cleaning out the Brake booster vacuum line wasnt a good idea. However, so far I didnt hear the pump running again and ASR didnt show up yet. I will test the car for couple of days and let you all know. Maybe I should just go ahead and spend $150 and get this new vacuum line, maybe it makes a difference. Weird problem but I am really concerned that this has something to do with vacuum system. Maybe a clogged pipe is causing the firmness or airpump is not enough at startups.

by the way I stopped at the local auto store to get a T to hook it up between booster and check valve to see values while car is running but unable to locate a Tee that fits to brake booster vacuum hose, I was reading that pressure should be somewhere around 0.70 or 0.80 psi and when I turn the engine off it should be around 0.8psi an shouldnt go below that is this true?