They say it should never light up at all? Well then what is it for? LOL.

Mine lights up with the other warning lights when I start the car and then turns off. I have yet to have it come on while driving, but I also have never broken traction while driving. It should come on if ASD activates though, which can only happen at slow speeds with loss of traction.

I did not know the '88's had ASD. I thought they started offering it in '90. Anyway, it sounds like yours is working normally unless I'm misunderstanding you.

 

Thank you so much for your confirmation that the lamp should light up when turning the key.
Unfortunately this does not happen with my ASD lamp.
Before I sent it for repair it was ligthing up from time to time when driving. At last it was lit all the time.
After the repair it never light up anymore, so I think they have removed the cable or something.
Does anyone know how to fault find on it. I heard there is a relay somewhere.
Anyone knows where to look for it?
Anyone knows how to remove the dashboard to check teh wires and bulb?
Thanks,
Henrik

 

Hi
the binnacle just pushes out from behind - or pulls out from the front...

the tools can be made from wire - coat-hangers work!

cheers

 

The ASD system really has two lights. The first light is at the right hand side of the bottom instrument and is marked "ASD". This will come on when you turn the ignition on and then go out. It will only come again if there if a fault is detected in the system. It does not come on to indicate the ASD is engaged.

The second light is a small yellow rectangle with a "!" inside of a triangle. It is located in the top part of the speedometer and it will come on when a speed difference of 2 kms/h is noted between the front and rear wheels indicating a slippery road condition. The ASD will automatically engage if your road speed is less than 25 km/h and disengage at 50 km/h.
Living in the great white north, unlike Chuck, that light comes fairly frequently during or shortly after a snow storm.

ASD was a rather expensive option available in Europe in the 80's (I have an 88 that was imported from Europe) and was never offered in America as a stand alone option except for diesel cars in the early 90's. It was standard as part of the 4matic system.

 

My bad...I forgot about the lower light...lol!

But, that doesn't change my experience too much. Both lights come on with the ignition and I have not seen either come on at any other time. According to my owner's manual, this is how it should work. It adds that only the triangle light should come on if you are moving and wheel spin is detected. If the lower ASD light comes on while the engine is running then the system is malfunctioning.

And london; I park the car in the garage if we get any white stuff. I'm confident in my ability to drive in it and I've driven other Mercedes' in it with surprisingly good results, but unless I absolutely have to go out, I just park and not worry about a thing! I suppose if I were to try hard enough I might be able to break traction in the rain, but since I'm old and slow now, I drive like I'm old and slow! This car is actually really hard to upset in the rain. When I lived in an area with 4 months of ice and snow on the roads, I had a 4WD SUV and a little beater Geo Storm with snow tires. Had I owned the Mercedes at the time, I'm still not sure I would have ventured out in it. I'm just REALLY protective of it...lol!

 

Must ASD Lamp light up? Reply to Thread

Thank you so mcuh all of you. Very valuable answers!
This really taught me how the system should work.
I have never seen my top Triangle light up.
I have only seen the lower ASD light up when it was slippery on the roads.
I might in that case have had fault on the system since I bought the car 2 years ago.
I believe I will start checking the instument dash board ASD lamp by removing it with a modified coat-hanger, to see if the repair shop just removed the wire or lamp in the lower part.
When the lower ASD lamp works with ignition on then I supoose I can start the fault finding using the short-circiut in the box under the motor hood and then count the blinking to learn what other sensors are faulty.
Any other hints are most welcome as I have no experience at all.
/Henrik

 

Was there a resolution to hm's issue?

I've fixed faults shown by code (one of the front wheel sensors) and while underneath pulled and cleaned the diff sensor, as well, even though it wasn't generating a code - only the right front wheel sensor (it and the left sensor were gunked up with brake dust and once zeroed out, the code didn't come back).

Is the module marked "ASD" the only computer involved? If the differential solenoid isn't working, would a code be generated and/or would the actuation simply not work? Or would the triangular light not work if the differential solenoid isn't working?

Yeah, lots of questions!

 

Is the module marked "ASD" the only computer involved?

Sort of. It's fed by the OVP relais. If the OVP relais has a fault, the ASD doesn't work.

If the differential solenoid isn't working, would a code be generated and/or would the actuation simply not work?

In theory, the ASD error warning light (the lower one) should light up. Simple test: Short pin 8 & 10 on the ASD's socket - oil should now flow. Put a hose on the bleed nipple on top of the differential and open the nipple. This also bleeds the ASD at the same time, which would be the next step in finding any faults

Bleeding the system cured my ASD completely

Or would the triangular light not work if the differential solenoid isn't working?

The triangle only lights up, if the ASD is in operation. If the ASD doesn't work, the triangle doesn't light up. It's there to inform the driver about loss of traction on the rear wheels.

 

Right, so the triangular light is illuminated when what happens? The solenoid is actuated? (assumption has to be made somewhere that this is the electrical signal generator, since there isn't a pressure sensor in the feed line?

The only bleed I found was on the side of the valve itself,the bleed bolt being just below and to the left of the solenoid ... is there another one on the top of the differential? (this is the valve assembly behind the fuel tank on the passenger side of the car)

Is it reasonable to just pull the entire ASD valve assembly, take it apart, make sure lines are draining with no blockages and that solenoid moves in response to 12v?

When I cracked the nuts on the lines there was some pressure, but not as much as I though there should have been, fluid poured out but didn't squirt (engine was running) ... this, combined with an early morning thought that I rebuilt the power steering pump in 2007 (has worked great since then) and perhaps I screwed something up since it also provides pressure to the ASD?

 

Right, so the triangular light is illuminated when what happens? The solenoid is actuated? (assumption has to be made somewhere that this is the electrical signal generator, since there isn't a pressure sensor in the feed line?

The triangle lights up, if a difference in wheel RPM between front & rear is detected. The solenoid only activates on speeds below ~18MPH. So yes, elet(ron)icaly. The light also lights up above speeds of 18MPH (that I know for very sure ). So yes and no...

The only bleed I found was on the side of the valve itself,the bleed bolt being just below and to the left of the solenoid ... is there another one on the top of the differential? (this is the valve assembly behind the fuel tank on the passenger side of the car)

IIRC there's a only a pressure-relief on the valve body itself... To release pressure from the pressure sphere (if present) / the system when working on it. The bleeding is done via the nipple ontop the differential (end of the line). It's a bit hard to reach on earlyer cars, on later cars it's facing to the front on the right side of the differential.

Is it reasonable to just pull the entire ASD valve assembly, take it apart, make sure lines are draining with no blockages and that solenoid moves in response to 12v?

When I cracked the nuts on the lines there was some pressure, but not as much as I though there should have been, fluid poured out but didn't squirt (engine was running) ... this, combined with an early morning thought that I rebuilt the power steering pump in 2007 (has worked great since then) and perhaps I screwed something up since it also provides pressure to the ASD?

Try to bleed it first. I wouldn't touch the valve body... Don't know if there's a rebuild kit available. The pump doesn't produce a lot of pressure on idle. If no fluid comes out the bleed nipple, you know the solenoid doesn't work...

 

Thanks, 200T,

Hmmm ... So, an inoperable solenoid will not cause the triangular light to not work or come on during the pre start sequence ...this means the lack of a light must be caused by a failure in the ASD module - assuming no broken wires or failed bulb (I've checked bulb and there is no indication of wire damage). Why wouldn't I get a code if this is the case?

It is possible then that the ASD system could be working without the triangular light being illuminated?

I'll locate the bleed nipple in next day or so ...I should bleed it while idling? I have a lift so I could have wheels up and transmission engaged if this would help during bleed? Could also have someone in car while on lift to apply more throttle ...?

So, you don't think the power steering pump rebuild could be at fault? It has worked great since the rebuild.

 

That's where I'm not sure right now... The ASD has a fault code for a non-working valve - but how this is detected? I don't know... IF the ASD computer detects a faulty valve, the triangle doesn't light up, but the ASD light in the right bottom of the instrument cluster lights up (permanentely).Hmm. Good question!

IIRC the triangle doesn't light up if you turn the ignition key if a fault is present - but I'm not sure right now... Never payed attention, so can't recall right now...

Bleeding as follows:
- remove ASD computer
- start engine
- bridge pin 8 & 10 (valve is now activated)
- bleed system from the nipple on differential until clear fluid comes out (use a transparent hose)

Re: power steering pump... Why not? I assume your car has the dual-pump (4 hoses)?

Any fault codes present in the ASD right now?

Fault code reading:

Bridge pin 1 & 5 on the rectangular diagnosis socket (next to the battery) for half a second. The ASD light starts to blink. Count how many times.

1x - no errors
2x - faulty ASD computer
3x - brake light switch (deactivates ASD valve)
4x - wheel sensor front, left
5x - wheel sensor front, right
6x - rear sensor (in differential)
7x - no input signals for ASD computer at all
8x - valve or brake light switch broken

Use a long cable to do it, or have someone help you, as the fault code is displayed immediately... To reset bridge the cable for about 10 seconds. ASD light goes off, blinks 1x to confirm ('no errors').

 

Bridged 8 and 10 ...applied power and can hear and feel solenoid moving ...bled at idle and got few bubbles so let flow a bit.

Rechecked and have one one flash so no malfunctions ... Except there is no triangle at startup sequence.

Will the test circuit see ALL malfunctions in the ASD module?

Pretty maddening and I don't have a couple of hundred bucks to buy a "what if" used module to test ...if I had full schematic I could get someone to test the module I guess.

 

Hmm. Maybe it's just a broken bulb then? Or did you check that allready?

 

Yes - pulled dash and checked bulb first thing ...summary, then:

Failure indication 1
ASD LIGHT DOES NOT EXTINGUISH AFTER START UP
- traced to code for right front wheel sensor; removed, cleaned and reinstalled both front wheel sensors and the speed sensor on the top of the differential
Result - ASD malfunction light came on during start sequence, then extinguished ...normal operation restored

Failure indication 2
TRIANGULAR LIGHT DOES NOT ILLUMINATE ON START UP OR DURING WHEEL SLIPPAGE
- pulled dash cluster and checked bulb
- checked hydraulic fluid level
- removed cover on ASD module and visually checked solder connections ...no indication of cracking or discoloration, etc
- bridged 8 and 10 connectors in ASD modules, applied power, confirmed solenoid movement by sound and feel, started engine and bled ASD from nipple on top, right side of differential
Results - triangular bulb not operating in any mode, cannot determine if ASD is operating during driving by feel

Anything else to check short of replacing ASD module or having it tested? It doesn't look complicated and the circuit scale is pretty large so should be easy to test (not my area of expertise, though).

Since the built in test system does not show a malfunction, is there one or is something else interrelated in some way that is not apparent. Everything else works fine, including ABS.

 

Ok, try the following. It wont solve the issue with the triangle not lighting up, but it'll show if the ASD works.

Jack up one wheel, start engine (P!) - that wheel should turn by hand with a slight resistance (35% locking abbility of the diff). Now bridge 8 & 10 again. If the ASD is working, the wheel should now me tight (100% locked). The diff should be warm, drive it a bit before you test it.

As for the light - I'm out of ideas... I suspect, there are scenarios the error detection routine doesn't recognise. Maybe trie a different ASD module? Even if all looks Ok...

Or try a different brake light switch. Maybe the contact is faulty and the ASD module 'sees' a permanently depressed brake pedal...!? I imagine this might not be detected by the ASD module as an error? Worth a try. IIRC they'r not expensive at the dealership

 

Great idea - i have it on a lift, so I'll lower it almost to floor, use a floor jack to jack up one of the wheels to keep it from moving, look for partial lockup resistance, jumper 8 and 10 and then apply key power and confirm the solenoid ports fluid to lock it up fully.

Situation 1
- (assumes both rear wheels aren't locked all the time due to solenoid being powered constantly and transparently)
- solenoid opens normally and lockup occurs (have already tested the solenoid so this will confirm if the hydraulic actuation occurs
- still unknown if ASD module is working in response to speed differential
- how can the ASD module be tested to determine if it is working?
- if ASD module can be shown to be working, then only the triangular light/light circuit is faulty

Situation 2
- solenoid opens normally and there is no lockup
- means there is something faulty in the hydraulic portion (but, this would be unrelated to the triangular light so now would have two issues instead of one )

Situation 3
- solenoid doesn't open normally and there is no lockup
- either solenoid is responding differently from previous shorting of 8 and 10 (not expected)
- and, still don't know if hydraulic portion is working, so would need to get solenoid working prior to be able to exonerate hydraulic issue

Best guess of what I should see from the bridging of 8 and 10 test:
- solenoid will operate normally (since have tested it)
- fluid will port (since there was fluid at the bleed)
- wheels will lockup

If all this happens, next test is to see if lockup occurs with the ASD module in place ... I have bene trying to think of a test on the lift, but all of them sound unsafe ...no snow, yet, here, so can't put it on a hill to watch from behind and see what happens from startup to drive to slippage to potential lockup ...

 

Test didnt work ... i have it on lift ... in Park with key off, both wheels turn whenever one wheel is turned by hand. With key on and 8 and 10 shorted, neither wheel will turn. Is this because transmission is locked in Park?

I also did some additional troubleshooting using the factory procedure for checking pin outs ... didn't get far, but found something not right - the manual calls for 4V from speed sensor input on pins corresponding to left and right front wheels (meter reads zero when wheel isn't moving) ... I got zero from left front and then 4V when turning it by hand. However, I got 8.15V from right front whether I was turning it, or not ... is this gonna take me into ABS? Something has to change the rotation speed signal into voltage, right? Does ABS do that for the ASD system? If so, the output from ABS coming to ASD is way off ...?

 

Quick read on passive wheel speed sensors - says they generate between 50-700mV ... so, ABS must take this signal and develop the 4V signal for ASD to use? (spinning by hand)

 

Durrr... I'm a dud I meant 'N', not 'P'... Fingers faster than brain... If both lock up, though - one should at least turn if P is selected. So - this would mean, the ASD is working, mechanically. I found out the hard way, that P is not enough to secure a car if you jack up one rear wheel... :surrender:

Hmm. Sounds like the sensor is not working correctly. Yes, the ASD module/ECU gets the signal from all speed sensors through the ABS ECU.

Hmmm. I'm runing out of ideas... LF sensor seems to behave correctly. RF sounds wrong. Where did you take the measurement? The sensors are magnetic and produce a/the current. The frequency of that current is used to calculate the wheel RPM.

I've read a bit further, and it seems the ASD ECU's logic can only detect NO signal from the speed sensors. Not a wrong one... So you might very well still be looking at a faulty FR sensor.

Hmmm. Complicated. How good is your german? I have the ASD technical bulletin/introduction here. But it doesn't contain any error finding routines, just a general description...

 

Yeah - neutral better

Procedure calls for VAC measurement between ASD plugs 3 and 9 for RF and 5 and 9 for LF...rest of procedure gets into the interaction between ABS and ASD so I guess I'll expand out in testing with multimeter and see what I come up with.

I will pull the RF wheel sensor, again, though and check it ... and if ASD only reports a fault based on "no" signal, then it indeed might still be that sensor ...so, ASD module would attempt to process it, come up with an unknown situation and simply not know what to do? And, I have to keep reminding myself this is related to the triangular light not working ...but, it sounds all interrelated.

German - not so good in this regard - I can order breakfast, coffee and beer, though

I (and anyone else troubleshooting ASD) really appreciate your help on this ...

 

Retried ASD solenoid test ... 8 and10 shorted ... On lift, one rear wheel with floor jack jamming it ...neutral with key off spins with sme resistance re 35 % lock ...key to start position and did not change the spin force ...started car and it locked up instantly. So, yep. ASD solenoid operates electrically and enough hydraulic fluid ports to lock it up.

Rechecked the RF wheel sensor through the ASD box ...still showing 8 VDC vice spec 4 V while spinning wheel 1/s (am assuming this means 1 rev per second). LF is right. 4.

I got about half of the tests done, but have to figure pin outs on the ABS harness to go further.

 

Ok, at least the ASD is operational

Yes, wheel speed 1 revolution per second - approximately. What's with the rear sensor? Does current pass through the brake light switch (it has two connections, one for the lights, one for the ASD)? I think the brake light switch is still a suspect here.

I tested my car yesterday night; no matter what I do, the triangle always lights up on start sequence. Ironically my ASD started to play up also - it doesn't allways detect wheel spin on the rear. AARGGHH!!!

 

It was the right front (RF) vice rear differential with the wrong test output ...it is still twice what is supposed to be.

I pulled the brake switch a week ago and used meter to determine it was working ... Also pulled the dash and checked the bulb ...however, I should have left it out so I could meter between the bulb and ASD sockets per the factory manual.

The triangle is supposed to illuminate during start sequence as test ...it is then supposed to go out immediately ...same for the ASD malfunction light.

 

200T,

Sent you PM to see if you wanted the test procedures doc for 126 ASD.

 

OK - so spent the afternoon troubleshooting using 35-516, going through every script except for the ones that required ABS testing routines - working backwards toward the ASD triangular bulb.

The RF wheel speed sensor is still showing 8.15V at the ASD module block when spinning the wheel once per second (approximately - per the 35-516 testing protocol).

I didn't find any open circuits - until got back to the ASD triangular light bulb base ... went through the wire connector, the small electronics board on the back of the bulb base, etc ... and, the bulb was bad. Odd since it tested fine 10 days ago when I was checking it first ... the Osram 12/1.2 bulbs are pretty common items so I got 4 (marked Philips 12/1.2 instead of Osram 12/1.2) and replaced the others in the cluster while putting it back together.

Connected everything back up and got the triangular light during start sequence and then it went out when the engine started.

Test drive - the ASD triangular came on several times as I exited corners without spinning wheels - sort of a hyper sensitivity to differential wheel movement, maybe? I checked the fluid level and it was no longer on the dipstick so am ordering some more to see if it was hydraulic fluid starved ... grasping as straws.

At least light is now operating per normal start sequence.

More when I get the oil and/or anything else weird happens.

 

Good to hear! And I can confirm that the triangle ALWAYS lights up when turning the key, even if a fault code ('ASD' lamp on) is memorized by the ASD module.

Funnily enough, my ASD starts to play up now... I have a 'knock' coming from the valve, I suspect a faulty pressure sphere. I have a ASD valve without the pressure sphere (later version) - is there any information, if they are interchangeable?