ASD problem on '94 E300D
 

We have a problem with the ASD light on a 1994 E300D . It's the trianglular light with exclamation point in the middle of the speedometer. It goes on at precisely 55 mph and stays on at higher speeds but goes off when speed drops below 55 mph again. We tried tires, the ABS/ASD Computer, the ASD control Module, the rear speed sensor, the over load voltage relay and also temporarily bypassing the brake switch. Any Ideas?
Thanks, Bubba

First off, sorry for resurrecting such an old thread.

My 1995 E300D is doing the same exact thing, but usually around 62-66 mph. The ASD light comes on when I spin the tires on grass, but the rear never locks. The car sat for about 2 years because of a blown motor, but is back on the road now.

I have tried doing the diagnostic test on the diagnostic port by the battery, but the light never flashes.

I know that this system is not well known but maybe somebody will know what's going on with my car.

Thanks

Check your tires are all the same sizes and are all properly inflated. The triangle light doesn't mean there is a fault, it means the system is actively seeing wheel slip and locking the diff, or attempting to lock in the case of a worn diff. This occurring only at higher speeds is b/c at lower speeds it doesn't interpret wheel diameter discrepancies as slip. At high speed there is enough difference that it thinks its slipping and is keeping the system engaged.

If you can confirm that all the tires are the same measured diameter only then would I look at the wheel speed sensors.

The tires are the same size and pressure on all four wheels. I don't think the system locks up at high speeds, I can't feel it. The ASD system is only supposed to work up to 16 MPH anyways. The wheel speed sensors may be corroded from sitting.

The biggest problem I have now is that when I do the diagnostic test I can't get any blinks out of the ASD light. Supposedly I need to put a jumper wire from number 1 to number 5, or just number 5 to any ground and count the number of times the ASD light blinks. Even if there are no problems it is supposed to blink once. It never blinks at all.

Thanks

Make sure you are using a hand-held LED blink code reader, and count the blinks on the LED reader - not the ASD light in the instrument cluster.

I just noticed something odd in the factory docs (attached)... it says you need to pull blink codes with the engine running at idle. If you hadn't done that, give it a try...

:detective:

First thing's first... are you sure there's no air in the system?

I also thought ASD didn't lock the diff over 25 MPH.

-J

ASD locks the diff up to 19mph, above that speed the warning light will signal the driver of a difference between front & rear wheel speeds, but it doesn't lock above 19mph. It functions as a normal limited-slip diff above 19mph. Full details here:

http://www.w124performance.com/docs/mb/other/ASD-ASR-4MATIC.pdf

Note that as the internal clutch pack wears out, the 100% lock will gradually reduce to near zero. Refreshing the clutch pack will restore functionality but it's a big job to take apart the diff to replace the clutches. The clutches are usually shot by 100-150kmi or so, but the lifespan will vary depending on how the car was driven.


:boat:

I opened a bleeder nipple back at the rear diff while the engine was running and the hydraulic oil came right out. If there was any air in there it wasn't much.

When you opened the bleeder did you have the ASD solenoid engaged?

I don't think so. The engine was running so I figured that the PS pump was pumping hydraulic oil around the circuit. But the ASD was not activated.

So I should jack up the back wheels, start the engine, put it in drive to activate the ASD, and then try and bleed it?

Thanks

I'd follow the FSM procedure. You remove the ASD relay, jumper some pins, start the engine, and open the bleeder. I can find the procedure for you later today if you don't have access to it.

-J