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94 s420 98 s420
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Discussion Starter #1
just trying to understand my car ( 94 s420 )a little better. While having the hood opened the other day i noticed there was a tiny rectangle relay looking on the left of the engine. it had a cap so i popped it off and found a reset button and what looked like an led light right next to the reset. what is this push button for?

Also while the engine was off i heard this pump noise under the hood, i traced this noise and it came from this little canister, on the right of the engine, near the diagnostic plug. Why did it go on and was curious as to what it was?

This is the first time that i own a car and not have any kind of a shop manual. kinda leaves you in the dark. Thanks
 

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1997 S600 (sold)
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4,660 Posts
Sorry, I'm not familiar with the S420 engine compartment, but

for as close to a manual as you can get, there is www.alldatadiy.com. Not a bad deal for US$25 per year. I've found it pretty good for my S600. The factory W140 CD ROM is available from various places now, too. I believe it's close to $200 at Mercedes dealership parts counters. I think someone here, jhodck or something like that, has them cheap. He just posted recently.

Brett
 

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1995 S600 (sold)
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1,127 Posts
I believe the LED is the built in fault code reader. I was told that W140's 94 and earlier had this feature. My 95 does not have this. I think the push button activates the code reader, as well as clears the codes. Pressing the button for four seconds with the ignition on retrieves fault codes. The LED will flash a code, ie 15 blinks. 15 corresponds to a fault code. Pressing the button for 9 seconds clears the faults. I'm also not sure how to isolate the different systems. Maybe a combination of pins have to be jumped? We really need to hear from someone who knows for sure. Check out Jim F's webpage. It's got a lot of good info.

http://pages.prodigy.net/jforgione/MB_S500.html
 

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92 500SEL to 01 E320T current 2014 lexus LS460
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Caliber motors in CA sold me mine, $158 +ship, there was someone showing it for less, but I can not vouch for it This was genuine MB from MB. The CD is copy protected and a DVD, you need a later version computer WIN98 or better Adobe...
 

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94 s420 98 s420
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539 Posts
Discussion Starter #5
Thanks for the link pcmaher, I pressed this push button and i received 19 blinks, would you happen to have what this read out is. also since i have this led, does this take place of that home made reader you did? How come the newer models dont come with this built in code reader or reset button, thanks for replying and ive been watching your harness project, nice work,its great info with clear pictures, thanks.
 

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1997 S600 (sold)
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4,660 Posts
Newer cars (well all cars sold as of Jan 96 in the US) have OBD II system.

ODB II (or OBD 2) = on-board diagnostics 2.

This is a government mandated diagnostic system required of all cars sold in the US as of Jan 1996. Mostly the system monitors emissions related components to force manufacturers to reduce emissions. It also forces consumers to comply to some extent as well, since an emissions system fault will light up the check engine light, and a lit-up light is an automatic fail in emissions testing. OBD 2 has a standard set of fault codes (same for all manufacturers), while there are a couple of different communications protocols that are used to read out information (fault codes, for example) from the car's computer. No more goofy blinking light. You get a code number on a screan when codes are read.

Many manufacturers have piggy backed a number of propietary diagnostics systems on top of the universal OBD 2 computer infrastructure. Fault codes for these systems are different and are manufacturer specific.

Brett
 

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94 s420 98 s420
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Discussion Starter #7
I had a 93 Cadillac Eldorado and i was able to retrieve the codes by pressing the warm and off button on the heater/ac control unit. It was very easy to do, and gave you active/history/snapshots of previous or current problems. Is my 94 benz considred to have an OBD2 or is this blinking light an outdated system. Also would you know what 19 blinks mean or where i can find refrence codes. I had the shop manual for the caddilac and every code was in there. If i had too much freon it would set a code and stop the ac from operating, resetting the codes was just as easy all done from your dash with a few buttons. The hood was ice heavy on the benz yesterday and fell on my head trying to fiddle with this reset button[B)] . However after buying this s class I would never want to drive another car, true love. until ofcourse i find out 19 blinks mean its a $3k fix.:)
 

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1995 S600 (sold)
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Brett did a fine job, as usual, of explaining OBD. Yes, your built-in LED takes the place of my home-built unit. Why newer cars don't have this LED, I can only guess at. Perhaps the OBD systems got more sophisticated, and required a more comprehensive method of conveying codes. It is really nice to be able to hook up a scanner, and simply read the fault on the scanner's display. I will see if I can find out what 19 blinks means. My manual is at home. I'll let you know what I find out.

p.s. I spliced my new home-made harnesses in the car last night. I notice an improvement in idle smoothness. I feel much better knowing that the wires are all good.
 

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92 500SEL to 01 E320T current 2014 lexus LS460
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Check Jims page he might have codes (*15 something about fuel injectors)
http://pages.prodigy.net/jforgione/MB_S500.html
 

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94 s420 98 s420
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Discussion Starter #10
I searched jims site and from my understanding hes selling the codes and other info on a cd.
 

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1995 S600 (sold)
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bass1175, I tried looking up what code 19 means in my manual. There are several different systems that have a code 19. What I don't understand is how the LED blinks convey which system has the stored codes. Maybe someone out there can assist?
 

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94 s420 98 s420
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Discussion Starter #12
I wondered the same thing pcmaher, what system is this code related to. How many possiblities does your manual show? I was on jims site today and he has step by step instructions on how to trouble shoot your A/C from the climate control and retrieve trouble codes.
his site is really helpful, he has all the climate control codes listed. with his steps i was able to tell outside temp, evaporator temp (usefull in the summer with the ac on)and that i have 0 pressure for refrigerant. Iam learning along and thanks to you and others who sent me links and tried to help out. check out jims link on this topic.


http://pages.prodigy.net/jforgione/MB_AAC.html
 

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92 500SEL to 01 E320T current 2014 lexus LS460
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As I recall, it does not go into diagnostics, I dont know what the CD has but I would think it would be the diagnostic chain along with component analysis. I looked at categoy (5), and 15 was some injector issues, and 19 was wide open throttle sensor.
 

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2002 s500, 2004 S500 fourmatic
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The fun begins!

If your fault codes are the same as mine, you could be into a new computer, but anyways.

The short description is that the built-in LED registers the DM module only. You need to do some research as there are a number of sub systems available to interigate(SP?) using a hand held tester that further define the problems.

I had the same problem and in the 95 W140 (420) it translates into "Fuel injector open/short circuit or self adaptation in LH/SFI control module (N3/1) at limit." Open/short easy enough to determine but if the adaptation is outside spec, you could need

(1) a new LH/SFI (I think) computer. (I can't remember is this is correct, but MB's solution is to replace the whole computer.)
(2) or other component in the LH/SFI system (ouch)

Check out Jim's web site as he sells a replacement prom for the computer that extends the limits of correction so that the existing computer if working correctly will continue to correct without sending an error to the DM.

By the way, any of these individual components are expensive. (I got lucky, Jim's chip solved the adaptation problem, but I'm probably looking at replacing MAS or something in the future.)

Tower
 

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600SEL, 300TE
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I have a similar problem of getting a DTC 19 on my 600 SEL. I think the fault in in the computer module 3/3 being at the limit. A previous reply in this thread says that Jim Forgione's site has a fix for this problem but I couldn't open his website. How can I contact him?
 

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85 300SL Euro,97 SL320,95 S420,07 S550
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I tried with the link I have book marked it looks like his website is down.
 

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94 s420 98 s420
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Discussion Starter #17
I delete this code and it comes back once every two months or so. I believe the problem for me is a bad wiring harness causing some wires to short,I dont notice any difference in performance but maybe a slightly rougher idle then normal, barely noticable. Iam almost sure mine ia a bad wiring harness. Fixing this very soon.
 

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93 BENZ 400 SEL
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425 Posts
Try this lnk for Jims site. I just went there and it is working :). It also has his Email link at bottom of page

http://pages.prodigy.net/jforgione/MB_S500.html

Have fun PGP
 

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Jim's prodigy site was down but is back up and running. I was able to contact him and have ordered new EPROMs for my two LH/SFI fuel control modules which will extend the self adjusting limit form the original +/- 15% to a new limit of +/-32%.
 
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