R129 CEL Diagnostic Trouble Codes & Procedures (1990-1995) - Mercedes-Benz Forum

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Old 06-14-2006, 12:37 AM   #1 (permalink)
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R129 CEL Diagnostic Trouble Codes & Procedures (1990-1995)

Could anyone give a short "how to do" on the diagnostic system for the old SL's?
I've tried the search function, but can't find anything explaining how to do it with what tool and a codelist.

Thanks in advance...
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Old 06-14-2006, 01:29 PM   #2 (permalink)
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The procedure described here works for all systems with diagnostics on the R129 through model-year 1995 except for the SRS (airbag) for '94 and '95. On some of the systems from '94 and '95 it will not retrieve as much information as an advanced scan tool would.

Each system's diagnostic output signal is wired to a specific socket of the car's main "diagnostic connector", X11/4. An additional pair of sockets in the connector provide battery voltage and chassis ground for convenience. Early cars with continuous-fuel injection have 16 sockets (picture), while later models have 38 sockets. The sockets are numbered for easy identification. When you make connections to any of the you should know that all circuits have protected outputs and nothing can be damaged by mistakes.

Codes are read sequentially one at a time. That is, you trigger the system you are checking to issue a code, you read the code, you trigger another code, and so on. With the key on and engine off, you trigger a code by electrically shorting the system's particular diagnostic socket to ground for 2 to 4 seconds using a wire. A second or two after the wire is removed, a series of electrical pulses will occur at the socket. The number of pulses corresponds to the number of a code.

There are numerous ways to view the pulses for counting and getting codes. The simplest method is to connect a 99-cent LED from Radio Shack (P/N 276-209, pictured) between battery voltage and the socket of the system being checked (the one you ground for 2 to 4 seconds to get a code) and watch it blink in sync with the pulses. A pair of banana plugs is nice for this. Be sure to have the polarity of the LED correct -- if it is wrong, you won't damage anything, but the LED won't ever turn on. In the special case of reading top controller codes on cars made through 12/93, you don't even need the LED -- just watch the top control switch on the console flash. This is possible because one side of the lamp inside the switch is wired to the diagnostic socket for the top control system.

Once you have read all of the codes you can erase them. They are erased individually one at a time. To do this, read a code, wait a few seconds, and then short the diagnostic socket to ground for 6 to 8 seconds.

For a list of diagnostic codes see post #3 below.

For diagnosing convertible top problems I believe it is best to read/erase all codes and then operate the top. When the problem occurs, continue holding the top control switch until it flashes or 80 seconds elapse -- whichever occurs first. Then read the freshly stored codes.
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Last edited by bobterry99; 06-20-2009 at 06:30 AM.
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Old 04-23-2007, 07:42 AM   #3 (permalink)
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Quote:
Originally Posted by edutain1
Thanks again Bobterry for this, I would like a set of the error codes, how should I go about getting them?
The codes are listed in a manual I have for a Baum diagnostic scanner. This is what I have been emailing to people and now realize I can attach to a thread (here). For troubleshooting procedures that follow the codes you should have either the Mercedes WIS software that can be bought from an eBay seller in the U.K. for about $10, or the R129 Tech DVD available from MBUSA for $75.
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Old 11-26-2008, 04:55 AM   #4 (permalink)
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hi i tryed but no luck i made a jumpwire between 1 and 10 2-4 sec the lamp was on i disconected the the jumpwire i got blinking ligth but the count was more then 40 then i tryed one more time same result
the hard top is on but i hade to do it manualy (the locking)
the car was fine two weeks ago now nothing is working its crasy when i lock the door the back rest goes forward so i had to remove the braker
the engeien fans dont work
the soft top dont work
roll bar same story

please help
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Old 06-29-2009, 07:46 AM   #5 (permalink)
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Quote:
Originally Posted by bobterry99 View Post
The procedure described here works for all systems with diagnostics on the R129 through model-year 1995 except for the SRS (airbag) for '94 and '95. On some of the systems from '94 and '95 it will not retrieve as much information as an advanced scan tool would.

Each system's diagnostic output signal is wired to a specific socket of the car's main "diagnostic connector", X11/4. An additional pair of sockets in the connector provide battery voltage and chassis ground for convenience. Early cars with continuous-fuel injection have 16 sockets (picture), while later models have 38 sockets. The sockets are numbered for easy identification. When you make connections to any of the you should know that all circuits have protected outputs and nothing can be damaged by mistakes.

Codes are read sequentially one at a time. That is, you trigger the system you are checking to issue a code, you read the code, you trigger another code, and so on. With the key on and engine off, you trigger a code by electrically shorting the system's particular diagnostic socket to ground for 2 to 4 seconds using a wire. A second or two after the wire is removed, a series of electrical pulses will occur at the socket. The number of pulses corresponds to the number of a code.

There are numerous ways to view the pulses for counting and getting codes. The simplest method is to connect a 99-cent LED from Radio Shack (P/N 276-209, pictured) between battery voltage and the socket of the system being checked (the one you ground for 2 to 4 seconds to get a code) and watch it blink in sync with the pulses. A pair of banana plugs is nice for this. Be sure to have the polarity of the LED correct -- if it is wrong, you won't damage anything, but the LED won't ever turn on. In the special case of reading top controller codes on cars made through 12/93, you don't even need the LED -- just watch the top control switch on the console flash. This is possible because one side of the lamp inside the switch is wired to the diagnostic socket for the top control system.

Once you have read all of the codes you can erase them. They are erased individually one at a time. To do this, read a code, wait a few seconds, and then short the diagnostic socket to ground for 6 to 8 seconds.

For a list of diagnostic codes see post #3 below.

For diagnosing convertible top problems I believe it is best to read/erase all codes and then operate the top. When the problem occurs, continue holding the top control switch until it flashes or 80 seconds elapse -- whichever occurs first. Then read the freshly stored codes.
Thanks for sharing the info with us. I'm new at the code thing and my sound like a dumb question but do the codes read out on the dash?
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Old 06-29-2009, 09:02 AM   #6 (permalink)
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Quote:
Originally Posted by boxco44 View Post
...do the codes read out on the dash?
Roll bar codes can be read by counting flashes of the malfunction lamp in the instrument cluster for '90-'95 cars, and top controller codes can be read by counting flashes of the lamp in the control switch for '90-'93 cars. All other codes require an LED, test lamp, etc.

Quote:
Originally Posted by bosnarrov View Post
hi i tryed but no luck i made a jumpwire between 1 and 10 2-4 sec the lamp was on i disconected the the jumpwire i got blinking ligth but the count was more then 40 then i tryed one more time same result
the hard top is on but i hade to do it manualy (the locking)
the car was fine two weeks ago now nothing is working its crasy when i lock the door the back rest goes forward so i had to remove the braker
the engeien fans dont work
the soft top dont work
roll bar same story
Late reply to an old post...

You should not have a blink count higher that 30, as only codes 1-30 are defined.
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Last edited by bobterry99; 06-29-2009 at 09:07 AM.
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Old 06-29-2009, 09:22 AM   #7 (permalink)
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thanks a bunch

Quote:
Originally Posted by boxco44 View Post
Thanks for sharing the info with us. I'm new at the code thing and my sound like a dumb question but do the codes read out on the dash?
i will be getting codes to day. Have not been able to drive my baby for the last six months
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Old 06-29-2009, 01:43 PM   #8 (permalink)
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hallo. i now its an old link but i try anyway. i am working on my sl now, read out fault codes on the roof, got code 23. RB controle module (crash deployment). tried to read out on the roll bar. jumped 1 to 7. the lamp was just lighting when i jumped but didnt blink after. is there a way to erase this code or is the RB module defect? the belt retractor on the passenger side is always retracted when you buckle up. the car has been crashed and fixed. Someone who got a clue?
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Old 07-22-2009, 06:20 PM   #9 (permalink)
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Date registered: Dec 2006
Vehicle: 1991 500 SL
Location: Prevost, Quebec
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code reading

I read the code on my 500sl 1991 and I have two questions about it, on socket 7 (roll bar) and on socket 12 ( Infrared remote control locking) I have two steady light when I plug in ( no flashes), and on socket 6 (supplental restaint system/ air bag) I have a light who stay on for about two second and come off, and no flash after. Anyone have a idea of what going on.
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Old 07-25-2009, 03:29 AM   #10 (permalink)
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If the LED lights but does not flash a code, there are two possible problems I can think of. First, the LED is not connected between #16 and the diagnostic socket being checked for codes. Second, a good contact is not being made continuously between the socket being checked and chassis ground for 3 seconds to trigger a read. If these criteria are being met, then possibly the diagnostic port of the relevant module is faulty.

Quote:
Originally Posted by Norwaysl300/24 View Post
the belt retractor on the passenger side is always retracted when you buckle up. the car has been crashed and fixed. Someone who got a clue?
I will guess that the seat belt's emergency tensioning device activated in the crash. If this is the case, then the seat belt must be replaced. If that is not the case, then the bowden cable that connects the seat belt buckle to the belt's take-up reel is likely jammed.

I have a good used one to sell, but I imagine it would be expensive to send to Europe.
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