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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Used ABS control units are on eBay for a substitution test....and they're cheap. I know you don't have a 4Matic but since the 4Matic brain talks to the ABS unit, many times the 4matic light being on is related to a faulty ABS unit. My point is.....don't assumed your ABS unit is above reproach.

Kevin
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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I agree - the only thing left is the electronic ABS control unit. In some ways, it's not a surprise since the modules in these cars have reached the age where things like cracked/crystallized solder joints and dried out electrolytic capacities are causing them to start failing.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Absolutely and older German electronics are full of 'cold solder' joints. Sometimes that is all to revive them....re-soldering.

The whole world of 80's & early 90's electronics was packed with leaking electrolytic Japanese capacitors. Those little blue bastards........

Kevin
 

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Discussion Starter #24
Status update:
I received a replacement ABS ECU and plugged it into the car in place of the original one (located behind the battery) and no change.
The ABS light is still illuminated on the dash cluster after starting the car.
I am at a complete loss as to what to do next.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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You need someone to diagnose the entire ABS 'unit' itself......I think, at this point.

Not replace, but diagnostic verification that it's 100% You can start with the FSM and see what they say about diagnostics and servicing the ABS system.
.
Kevin
 

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Discussion Starter #26
See an earlier posting in this thread. I have already taken the car to a local MB specialist shop where they used a factory ABS diagnostic tool that plugs into the harness in place of the ABS ECU to test the system.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Well, according to them, they thought there was an intermittent problem with a relay inside the ABS pump unit. I'm not convinced they were 'experts' with respect to your car's ABS system. But you're asking us to diagnose and unseen car with no hands on and no tools....good luck with that.........unless someone chimes in that had the exact same problem. There's always the possibility......

Kevin
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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That is a bummer!

A few more thoughts . . .

Hydraulic Unit: As I read the thread, the one thing that has not been replaced is the hydraulic unit. Did the dealer say they tested the resistance of the wheel control solenoids when they had it on the test harness? The resistance of each one should be 0.7-1.7 ohms. I believe that the ECU "tests" (although it is not clear if this test happens at start up or at 3MPH) for an open solenoid and so if you have a bad solenoid, that would trigger an ABS light. Did they verify that the pump motor runs? A similar test may also performed on the return pump motor, so a bad (open) motor could also cause an ABS light.

ABS Harness: You may have an open connection in the ABS harness (although not likely if the dealer conducted all of the tests the service harness will support). It may sound dumb, but try wiggling the harness at each of the connectors while someone monitors the ABS light. If it flickers/goes out, there is an issue with the harness.
 

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Discussion Starter #29
This is the type of ABS factory scan tool they used:

MERCEDES ABS TESTER W126 W124 W201 (link to ebay listing for same tool)

They did say the wheel sensors were definitely within spec.

BTW, it was not a MB dealer. It was a local MB specialty shop that has many years of experience working on MB cars and are well respected in this area.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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They did say the wheel sensors were definitely within spec.

BTW, it was not a MB dealer. It was a local MB specialty shop that has many years of experience working on MB cars and are well respected in this area.


Right, but they didn't fix it. Somebody good on these cars isn't going to let it just leave unsolved. Maybe you gave him monetary limits....we don't know.

Kevin
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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This is the type of ABS factory scan tool they used:

MERCEDES ABS TESTER W126 W124 W201 (link to ebay listing for same tool)

They did say the wheel sensors were definitely within spec.

BTW, it was not a MB dealer. It was a local MB specialty shop that has many years of experience working on MB cars and are well respected in this area.
Yes, that is the correct tester (I wouldn't mind having one, but not for that much coin). And with that that should have been able to verify the wheel control solenoid resistance along with testing the operation of the pump. Did they do that?
 

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I've never been inside the ABS or even under the plastic cover. Flooby do you think it might be possible to isolate each solenoid and substitute a resistor to bypass each one individually to see if one is causing the light to go on?
 

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Discussion Starter #33
Another strange thing about this car (again a 1993 300TE w/3.2L M104 motor) is that the end of the ABS harness that is supposed to plug into the top of the ABS ECU does not actually fit the ECU socket correctly. The original ECU that is in the car and the replacement ECU I got the other day have a tooth at the engagement end of the plug like this:

2634969


But the end of the harness that is supposed to plug into this part of the ECU has no matching slot to engage with this tooth.

2634970


So in order to get the harness to actually plug into the ECU I have to undo the two screws that hold this aluminum piece onto the ECU and remove it so the toothed piece is not there.

2634971


I have called two different MB dealers to ask if the part number on the ECU matches with what my VIN number shows the car should have and they have confirmed the ECU (the original one and the replacement one) are correct for the car.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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We have a poor search feature for past threads.....but some yrs ago a member went inside the ABS pump unit itself and found dried up grease and a number of ills. It's kind of illogical to think that these units would go on forever without some sort of rehab. However, his problem was not the ABS trouble light as I remember it.

I have to think your problem is more electrical/electronic in nature.......but I wouldn't rule out the pump unit itself just yet.

Kevin
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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The connector issue is definitely not right. Has your car always had the ABS light on or did this come on recently? Is there a part number on the ABS harness itself? Perhaps it was replaced and the incorrect harness was installed.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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I've never been inside the ABS or even under the plastic cover. Flooby do you think it might be possible to isolate each solenoid and substitute a resistor to bypass each one individually to see if one is causing the light to go on?
I think that would be difficult to do. I think it is best to just measure the resistance of the solenoids in-situ.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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The connector issue is definitely not right. Has your car always had the ABS light on or did this come on recently? Is there a part number on the ABS harness itself? Perhaps it was replaced and the incorrect harness was installed.
There's merit in this statement....PO's have a bad habit of swapping out things from JY's and then flipping the cars. He could very well have the incorrect harness.

I went back and reread the OP's first post. The car was in dry storage a long time from another owner. It would appear that the ABS light has been on since he purchased the car.

Kevin
 

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Discussion Starter #38
Is there a way that I can jump some of the relay pins under the cover of the ABS pump to see if the pump functions?
 
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