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Old 08-03-2001, 12:16 PM
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ECM/ECU completely shot????

I have a 1995 Mercedes S420. The check engine light is on. The car is running fine. The dealer claims (after charging $80 to check it) that the whole ECM is bad and needs to be replaced because it is not reading the information coming from the injection system. They called it a "hard fail", I thought the car would be in limp mode if there was any hard fail. Anyone got any advice on this? The part alone is $2100 at the dealership, and I have a hard time accepting that its bad to start with. Thanks, pardon me if I broke any rules of etiquette, I am brand new to this forum.

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Old 08-03-2001, 03:20 PM
David C Klasse's Avatar
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Join Date: Jan 2001
Location: Mission Hills in the City of San Diego
Posts: 2,352
Go to an independent mechanic, preferably one that specializes in Mercedes and see what they can come up with. The dealer will rip you off! Probably a load of BS anyway! Good luck.
2006 E350 w/ 155k miles (Daily Driver)

1993 300E 3.2L Sedan w/ close to about 300k miles
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1989 300E with 289,000 miles (had for <1 yr while in HI)
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Old 08-04-2001, 09:34 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
If they are wanting to replace the LH controller, they could be correct. There was a Service Information bulletin on this subject where the adaptation parameters were too tight inside the controller. When hot weather hit, the contoller would take the engine to the lean or rich stop.
Donnie Drummonds
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Old 08-04-2001, 10:05 PM
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Join Date: Feb 2001
Location: SE PA
Posts: 63
I agree with David C Klasse. Even if the dealer is right, you'll have the confidence that comes with an independent second opinion. Add the option of looking for a good used one at a fraction of the dealer cost and plugging it in yourself and the outlay for diagnosis at a second shop looks like a pretty good deal.
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Old 08-05-2001, 10:23 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I would really like a technical discussion on the code 19 issue. Donnie jump in here.

I don't know if that is the issue here, but I just dealt with a 600SEL (1992) that had just come from the dealer who wanted to put two new controllers onto it for the code 19 issue.

I'm going to write down what I did and what I found and see what comments it draws:

The car came in first with the customer waiting. The customer has had the car some months after purchasing from a local wholesaler, who is accepting my costs to deal with the MIL light after not accepting the dealer suggestion. I reset the code 19 on the diagnostic module. There are no codes on either LH module. After a couple weeks the car is scheduled in for the diagnostics that we knew would eventually be necessary.

I checked and the situation had returned. With my scanner I viewed actual values. The O2 sensors were very slow and one of them would stop and go open loop after a short idling period. I replaced both sensors. This fixed the problem with open loop. I also had been watching the adaptation values. The car came in with lower partial adaptation at .87, upper partial was .91 After resetting the code and the adaptation values (to 1.00 it took two days of driving before the values reset themselves back to slightly higher settings (since the O2 sensors were replaced).

Reading a bunch and talking on some tech sites I became aware that I could reset and relearn the car on my dyno in about five minutes once I set the load right and got the technique. Basically I reset the adaptation to the 1.00 and then ran the car at 1600-2200rpm and 40-80kg/hr load. Then I would run the thing to 3500-4500 rpm with 150-300kg/hr load. This would set the lower and upper partial adaptations. These readings I repeated numerous times and consistently got .87LP (lower partial) and .92 UP on the LH1 bank and .91LP and .93UP on the LH2 bank. I reversed the AMMs (air mass meters) side to side and the readings reversed. I ordered a new AMM (didn't know that they were offered rebuilt or I would have gotten both as the list price was only $215 for the MB rebuilt unit).

When I got the new unit in the values went to .94LP and .94UP (on the new one) and .92LP and .93UP (on the better old one).

The car left Friday with a $600 bill to the wholesaler. Only time will tell if I provided a lasting repair.

The issue here is that the early controller has only the ability to change the base mixture by about 15% from base calculation: .85 to about 1.15. The new controllers have changed the capability to maybe as high as .68 to 1.32. These figures are semi alluded to in a WIS article GF07.xx can't remember the rest; I have it bookmarked on my WIS.

I also found something interesting talking to one of the techs. In WIS that article will appear on a list if one types: GF07% into the document number slot. This will give a list of all GF type documents in group 07.

Sorry for the length of this post and the fact that it may be too technical. Donnie brought up the subject and we will have to talk some of this in private but I am still interested in opinions and comments.

If the darn things weren't so expensive I would say that the new controllers are the best answer even if they aren't really solving the problem just compensating for it. This sounds like a good thing for MB to subsidize with a rebuild program, especially if the hardware doesn't need much changing.

BTW the runs on the dyno consistently got worse as the car heated up (which it does much more than on the road where it gets more air - the car never got above 200 on the road, but got to 220 in testing before we took a break).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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