Reading Codes - PeachParts Mercedes-Benz Forum

wjm · #1 08-04-2003, 03:38 PM

Folks,

A few posts recently has gotten me to wonder about this issue.

In my vehicle (94 E420) I can read codes that are stored in my vehicle. I assume that codes are stored whenever the Check Engine light is on.. and no code when it is off.

According to JimF's site (https://www.k6jrf.com/MB_S500.html),

there are many modules that send out codes (all have different sets):

Distributor Ignition Module [DI] DTCs
Diagnostic Module [DM] DTCs
Hot Wire, Sequential Fuel Injection Module [LH-SFI] DTCs
Base Module [BM] DTCs
Electronic Accelerator/Cruise Cntrl/Idle Speed Cntrl Module [EA/CC/ISC] DTCs
Anti-lock Brake System w/ Acceleration Slip Regulation Control Module [ABS/ASR] DTCs
Supplemental Restraint System [SRS] DTCs
Anti-Theft Alarm System [ATA] DTCs
Convenience Features [CF] DTCs

My assumption is that the little push button and LED in my engine compartment (I think it's called X/11) only reports out codes from the Diagnostic Module. Is this correct?

This car is not ODBII compatible as it is a pre 96 vehicle. Without spending $$$ on an elaborate reader, is there a way to check for codes in other modules?

I have read posts about a Craftsman Digital Volt Meter that can be used to read codes and other data from the vehicle. Can someone elaborate?

Arthur Dalton · #2 08-04-2003, 04:14 PM

CE lamp is activated by DM only... access is with built-in led/sw.
All other modules are accessed with a home-made led tool.
[which is nothing more than a copy of the built-in led circuitry, but with its own leads]
see archieves for tool ..the are several ways to make one for about $5..
You can then go into the other pins on the diagnostic plug for specific code storage..

wjm · #3 08-04-2003, 04:25 PM

When you mean "home brew", do you mean what JimF has documented on the bottom of this page:

https://www.k6jrf.com/MB_S500.html

Are there instructions on how to use one of these once you build it?

Also, what exactly is it that you can do with the Sears / Craftsman DVM that everyone talks about?

Arthur Dalton · #4 08-04-2003, 04:36 PM

The Sears meter you read about is popular here cuz it has both Duty cycle and Freq. cababilities for the earlier duty cycle systems..
but you have a Flash system and that only requires a 12 volt led and sw circuit.

That one will work...there are others ..

wjm · #5 08-05-2003, 09:42 AM

But how do I read codes from the Alarm (ATA) system or the convenience system? If those systems (or others) are generating codes, I would NEVER know about them, as the check engine light would never be turned on for those.

According to Steve Brotherton's DIY article: http://www.peachparts.com/Wikka/EngineControls

Quote:

This process of reading codes for these early systems works up to 1994 for all systems, and later on some systems. Basically, it will work up to OBD II systems, and applies to all systems, not just engine management systems. The code retrieval method is very simple. The communications take place over a single line on the appropriate diagnostic connector. On the car I used (a 1991 300TE), the connector (X11/4) is located next to the battery, next to the right side hood hinge.

The KE controller is accessed on data terminal #3. With the key on, engine off, self-diagnostics is activated by grounding the #3 pin for two to four seconds. Once this takes place, the control unit transmits the codes by itself, grounding the #3 terminal. (Remember that all systems work the same; all you need is a directory of which pins to activate and the code table to interpret.)

So, all I'm looking for are instructions on how to read codes for all of the other modules.. either using a DVM with duty cycle or building one of these LED things.

I'm sure that the following pictures from JimF's site hold some clues.

https://www.k6jrf.com/MB_S500.html

Arthur Dalton · #6 08-05-2003, 09:50 AM

The led simply has 3 leads .. one goes to bat +, one to - , and the other goes to the designated pin # on the diagnostic connector for which system you want to get the codes on...

There are four different connectors .. which one do you have???

wjm · #7 08-05-2003, 10:09 AM

Ahhhhh.... now I get what you are saying... I should read more carefully.

My car has the the button and LED. I believe that it is called "X11/21"
It also has connector (X11/4) as shown below.

So, you're saying that if you make the 3 wire LED, you plug one to battery +, one to battery -, and the other to the correct plug in the "X11/4"?

How does the led tool work once it's built... do you simply plug it in as I said and turn the ignition key to "on"?

Arthur Dalton · #8 08-05-2003, 10:22 AM

Correct..
You had me confused as you have all the info right there ..
As stated, The led tool is simply a portable led/sw replica of the one you have on the car..
so, if you look at the 38 pin connector and the chart ID , you can see that the tools +[pos/red] goes to pin 3 for power,
the - [ neg/black] to pin 1 for ground, and now the test pin goes to whatever pin/module you want to get the codes from..
[Many guy just put alligator clips on the tools pos/neg and just go to the battery for powering the tool, as they use them on different systems]
The procedure is the same as the built-in LED/SW..
thats all...
then you go to the code ID chart for that particular module/code meaning.....

Duty cucle is not for this system..

wjm · #9 08-05-2003, 10:28 AM

Awesome. Thanks.

Since my battery is in the trunk, I'll have to use 1, 3 and other.

I'll post back when I get it built. Again, I'm assuming that once you get it built and plugged in correctly, you simply put the ignition key to "on" with engine off and light will blink if you have a code... right?

Arthur Dalton · #10 08-05-2003, 10:38 AM

Quote:

Originally posted by wjm
Awesome. Thanks.

Since my battery is in the trunk, I'll have to use 1, 3 and other.

I'll post back when I get it built. Again, I'm assuming that once you get it built and plugged in correctly, you simply put the ignition key to "on" with engine off and light will blink if you have a code... right?

yes . 1/3 for power .. I put that there cuz I know your bat. is in trunk...

As to light the led . it does not just work.. you have to press the sw and hold for 2-3 sec., just like the built-in one [ this is code initiation signal to the module]...just remember, code retrieve is the SAME procedure as for the the built-in procedure... you are just expanding to other pins over the built-in led.
Nothing else is different...SAMe retieve, SAME Clear procedues..

RS has a led with a built-in resistor [ part# 276-209] that will allow you to eliminate the dropping resistor in the earlier tool
schematic..if you have trouble with the schematic, email me for a pictoral diagram with RS part #s...

wjm · #11 08-05-2003, 10:46 AM

Thanks.

Yes, the only schematics I have is the one from JimF's site (below). I think it's the older one. I'll PM you my email addr.

JimF · #12 08-05-2003, 11:40 AM

post and thought I'd reply so as to see what happens.

Just be careful when you plug in the "TEST" lead: no shakey hands needed!!

The instructions apply for all pins being tested: 2 - 4 secs to "interrogate" and 7 - 9 secs to "clear" codes. Remember that you need to clear EACH code: so after reading the codes and writing them down, you must go back and start the re-read cycle but this time resetting EACH one individually by holding the pb down for 7 - 9 secs within 10secs after reading the DTC. Clear??

wjm · #13 08-05-2003, 12:10 PM

Jim,

I understand that this works just like the built in LED. I do remember, though, that you may need to turn off the ignition between code clears for it to work (this is from memory.. so I'll have to check).

Also, what can happen if I plug the test LED in the wrong #? Any damage that can occur? If so, can you post (for sake of completeness here) which #s correspond to available DTCs?

JimF · #14 08-05-2003, 03:35 PM

I do remember, though, that you may need to turn off the ignition between code clears for it to work (this is from memory.. so I'll have to check). Turn of the ignition for 10 secs or so. Then continue to read and erase. Now I use a scanner so it does ALL of the codes at once.

Also, what can happen if I plug the test LED in the wrong #? Not much, wouldn't worry about it.

Any damage that can occur? Maye shorting two pins where one is ground probably would do some damage.

If so, can you post (for sake of completeness here) which #s correspond to available DTCs? You car should have the same systems (pin population) as mine. You can tell by looking to see if there's a female pin and noting its pin number. Then compare that to the function list to see what it is.

#15 08-05-2003, 05:22 PM

Jim,
I read your write up on the palm scanner, is that the scanner you are currently using?

I have not used a scanner before. I have a 97 s420 that has the individual electronic ignition modules on the spark plugs. Will the scanner be able to tell me which one is bad if one should fail?

I'm trying to decide which scanner to buy. I read a thread by Steve about the SnapOn MT2500 scanner. He said that the MT2500 will give you about 75% of the information about a car as compared to some other OBDII scanners that only give you 10%.

Having tested the Palm scanner what are your thoughts?

Thanks,
Tom

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