ASD troubleshooting - partial success - PeachParts Mercedes-Benz Forum

stephenson · #1 12-27-2012, 10:37 PM

Finally got back to the ASD issue - after several years of other distractions.

The rectangular warning lamp was lit during start sequence and after start - didn't go out. So, Pulled codes using homemade tester and by jumping #5 to ground to read the flashes on the warning lamp - right front wheel sensor was shown as faulty so pulled it and degunked the tip where there was a lot of brake dust buildup, did same with left wheel and the differential speed sensor.

Reset the code and tested codes after a couple of days of driving. Got none. However, the yellow triangular lamp never lit - I spun rear end around on a gravel area near road and watched for the lamp to light, but never did ...is there some way to tell seat of pants if the ASD is working? Shouldn't it flash as the rear wheel lose traction?

Some of threads indicate the triangular lamp should be lit during start sequence - mine is NOT - I don't recall it ever being lit during start - could it simply be bulb? If there is no other indication in feel, is there anything else I am missing or should I just pull cluster and check the bulb (I've done cluster before and hate it :-))

biopete · #2 12-27-2012, 11:19 PM

Check that bulb. It should light with key turned on and definitely flash when spinning out in gravel. What about if you hit the switch? It should stay on. Maybe there is a fuse for it?

stephenson · #3 12-27-2012, 11:29 PM

BioPete,

My 350 SDL doesn't have a switch ... Ya think the triangle bulb should be lit during startup sequence regardless of other potential malfunctions? I was going down this path, as well ...just don't have enough info to conclude that.

Dr. Sternschnuppe · #4 12-28-2012, 10:14 AM

Is the "ASD" lamp flashing up when ignition is on?

stephenson · #5 12-28-2012, 10:28 AM

Dr S,

Rectangular "ASD" light on bottom row right lights during start sequence with key on, but goes out when engine starts. Triangular light does not light during start sequence, or when rear tires spin on gravel.

Dr. Sternschnuppe · #6 12-28-2012, 01:10 PM

Check connection between the ECU and the "triangular" lamp, electronic components of the "triangular" lamp system, also check bulb. If all is working properly, the electronic control unit of the ASD is damaged.

stephenson · #7 12-28-2012, 02:42 PM

So, removed the cluster and checked bulb continuity ...both large background light bulbs were about 5.3 ohms and tiny ASD bulb was about 21.5 ohms (I can't tell if bulb is a part of the base assembly or if is replaceable) ...will start working way back to the ASD control unit ...I pried control unit apart, no points or contacts of any kind and it did not look burned.

Light tunnels were dis colored pretty badly so will spray them white and reinstall after metering for break in wiring.

stephenson · #8 12-28-2012, 05:29 PM

Applied 12v to ASD bulb and checks out fine ...when on start sequence all I get is 3.5 v between two of the three light pins ..

Painted light tubes and reinstalled cluster ...way brighter ...bulbs looked OK so just used over.

stephenson · #9 12-29-2012, 12:34 PM

So, at am impasse - built in test for ASD says there are no faults ...malfunction light comes on during start sequence and then goes out (normal), but triangular ASD operations light does not come on during start sequence nor does it illuminate with rear wheels spinning around a corner from a stop.

What else can I test? The ASD module under hood ...anyone have test procedure for it? Anyone have one I could test with, or purchase (assuming cost benefit makes sense :-))?

stephenson · #10 12-30-2012, 08:27 PM

So - thinking about the triangular light - does it mean (1) the ASD system is working (sensors provide data to computer and computer tells solenoid to port fluid and the solenoid moves and ports fluid), or (2) the sensors provided data to the computer and it senses differential speed?

In (1) how does the solenoid circuit work? Does it feed a signal back to the computer and tell it turn on the triangular light?

I bled hydraulic fluid from all the lines at the solenoid and pressure reservoir near the right rear of car ... looked clean. How does one troubleshoot this device - or, do you simply pull it and take apart to ensure solenoid is working and the fluid is being ported?

Thanks!

stephenson · #11 12-31-2012, 10:14 AM

I'm gonna keep at this, I think ...

So, during line-fluid check yesterday, the engine was running, so there should have been significant pressure on at least one of the lines, right? The one coming from the reservoir? And, the ASD uses the power steering pump to create pressure for actuation via the solenoid porting fluid?

OK - I rebuilt the power steering pump in 2007 and it has operated flawlessly since then ... could I have screwed up the pump rebuild in a manner that would allow power steering to work fine, but not the ASD?

Putting it all together because I don't think there was any real pressure from any of the lines .. what operating pressure should there be? Enough to squirt out of just drain out quickly (all I got when i cracked the line).

stephenson · #12 01-08-2013, 06:59 PM

Well, today things got better .... finally.

Today I removed the RF wheel sensor, and carefully examined it, the wiring from the sensor to the grommet at the wheel liner, the knuckle where the sensor is attached, and the tone ring. Not finding anything unusual, I carefully cleaned the sensor, sanded the outside of it lightly with very fine sandpaper, including between the two tips on the end of the sensor, sanded the base plate where the sensor attaches, sanded the inside of the sensor mounting plate, sanded the inside of the sensor receiving tunnel, carefully cleaned around the base of the tip of the sensor with a small tipped awl, inserted the awl through the access tunnel and used the tip to clean every tooth in the tone ring, then sprayed everything with brake cleaner, using compressed air to completely remove any disturbed material.

I then tested the output of the RF wheel sensor and found it, again, to be 8.15 VDC with ignition on, but when spinning the wheel at 1/s it now at 4 VDC (the spec number)! The LF wheel always tested 4 VDC with wheel spinning, but always tested at zero (0) when the wheel was not spinning.

Put it all back together and everything worked per spec – the ASD triangular light illuminated during start sequence, the ABS did no actuate during stops, the ASD triangular light illuminated when I accelerated and spun the wheels on a gravel/dirt road and then went out per spec.

A good exercise in troubleshooting!

Dr. Sternschnuppe · #13 01-10-2013, 10:43 AM

Grats!!!