ASD Triangular light not illuminated
 

I started a post on this, but the issue and troubleshooting has expanded, so I am summarizing in this post with the hope of getting additional thoughts. The original post is at: http://www.peachparts.com/shopforum/diesel-discussion/332525-asd-troubleshooting-partial-success.html, and was getting assistance from 200t on another forum, and that post (in 124 forum but with som diagrams) is at: Must ASD Lamp light up? - Benzworld.org - Mercedes-Benz Discussion Forum.

Here is summary:
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.

This experience should be helpful to others, so I really wanted to document and work it to closure.

Thanks!

Even though didn't get a code from ASD test, I continued troubleshooting with factory process for testing module connectors ... found something weird very quickly ... the front wheel speed sensors are supposed to read zero V at the module interface block (read with meter between the specific points) when not turning, and 4V when you spin the wheel by hand. I got zero on left front and then 4V when spun, but on right front, I got 8.15V both stopped and spinning.

Again, I have no codes from the ASD module - is this something it would not recognize? Is the 4V signal developed by the ABS for the ASD system or do both ABS and ASD simply get the signals in parallel with one another? If in parallel would the ABS see this difference as a fault?

Quick research on passive wheel speed sensors says they should put out 50-700 milli V ...so, ABS must be developing the signal for the ASD?

Was able to trick the ASD solenoid into operation - with car on lift I used floor jack to immobilize one of the rear wheels to prevent turning - jumpered terminals 8 and 10 and put in neutral - got some lockup by spinning one of the wheels - then had someone turn on key to start position without engaging started - no change in lockup and could still spin the wheel. Helper started engine while wheel was being turned and the differential locked up immediately. Basic test to confirm ASD solenoid is working.

Spent afternoon troubleshooting using 35-516 protocols starting on page 669, going through every script except for the ones that required ABS testing routines (some interact with ASD system) - 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). It should be approximately 4 VDC. Left wheel sensor reads 4 VDC per spec.

I didn't find any open circuits in wires or connectors - until got back to the ASD triangular light bulb base ... I had tested 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 - different manufacturer but same markings for wattage and base) 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 per normal.

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.

George,
Let me stir the pot a little. I go into "limp home" every morning and no lights come on. However when I start up, both lights illuminate. When I break the rear end loose going around a corner, the triangle lights. Why doesn't it light when I go into 'limp home"?
Is this a German plot because of WWII?
Anziani

Anziani,

Not sure what mode limp home is ... are you talking about an engine management limp home or transmission limp home ...in either case, not sure how ASD operates within constraints of limp home. And, to be clear, you are talking about ASD?

"Limp home" is the system that forces the driver to push the gas pedal to the floor for any acceleration. It occurs with failures in various components in the system. I only know of engine limp home. Have never heard of transmission limp home. There are volumes of posts on limp home, the Benz curse of the '90s.
The harness, the ETA, different sized wheels, bad brake light switch, bad ASR computer, bad E-Gas controller, etc. will contribute. :overlord:
Anziani

Anziani ...did you resolve your issue? Do you have ASR or ASD? ASD won't cause limp home mode ...don't know about ASR ...sounds like something bigger going on.

George,
Apparently I have ASR even though it doesn't have a silk screened logo. The ABS unit has a black box so that seems to be the determinator. Yesterday was an example. It is cold here (at the moment). When I left the house it was about 36F. I let the car warm up for 5 minutes and took off. I went into limp home about 3 times before it finally reset. I then drove 200 miles, had a meeting and headed back home. Three blocks from the house it went into limp home twice. There is NO lamp lit but I know the triangle lamp works because I can break the rear end loose and it lights.
This latest limp home with a warm engine has me really spooked.
Anziani

Anziani, I don't think I can help ...the limp home mode may not be related to the ASR...but to some other issue ...what little knowledge I gainedmis related to the ASD system and niter actions with ABS.