Reading Codes
 

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?

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..

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?

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 ..

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

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

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???

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"?

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..

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...

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.

Willy, just came across your . . .
 

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??

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?

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.

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

The Palm Scanner [PS] fills the void . . .
 

between the high end stuff, AST Retriever and the LED/Sw combo (biuld it yourself) DIYer tool.

The Retreiver costs $2300 making it, to my mind, a high price tool. Would love to have one since it can do LIVE data, reading the S/A (self adaptation), firing/mis-firing, O2, MAF data, etc.

The PS just reads and resets codes from 1988 thru 2002. It does not do what any LIVE data. I'm sure the SnapOn device probably does that but not familiar with it.

Actually, the newest/latest versions have added such goodies as a 'scope' which you would appreciate. Then you could "see" the misfire. But if it is failing (even intermittantly), the Retreiver would catch it in the LIVE data mode. But for me, the price is just too high.

I would stay away from just OBD scanners as Steve suggests; if it can give Mercedes type codes and OBD, then ok.

I've use the PS and it's a good tool taking its limitiations in mind. The PS is great deal for the price (send me an email). Depends on what you NEED to do.

OK, I got it built... but I just noticed I got the wrong connectors put on the ends. I thought the tiny 3/32 Mono phone plugs would fit into the holes of the 38 pin (X11/4) diagnostic connector.. I was wrong.

I just noticed that on the module that has the LED display, there is a spot that I can tie into the #1 and #3. I tested it and it has just under 12 volts, so that must be tied directoy to the X11/4. I can use the banana plugs for those.

I'll have to figure out how to get the 3rd plug (yellow) into the x11/4... maybe I can use something thin like a paper clip and then use an alligator clip (in place of yellow) to grab the clip.

Let me rephrase my last question.

Can I use banana clips for + (red) and - (black) and connect them to the X11/21 (LED connector) #3 and #1 respectively? This is not the X11/4 38 pin connector.

Also, what do you recommend I use for the yellow (test) connector that gets plugged into the X11/4 connector? (ie... #23 for testing Alarm DTCs). The only though I had was to stick a staightened out paper clip in the hole and use an alligator clip on the test wire.

Sorry, I didn't reply because. . .
 

you planned 'attack' looks ok to me. Pin #1 (ground) and Pin#3 (12V) will be just 'dandy' to use.

Need to get a pin that will fit nicely into the holes without damaging the pin. Check some surplus electronic houses in your area and look for some old pins from military connectors. You should be able to find one that will fit nicely.

But if a paperclip works, then use it. Would suggest that you solder it and then use a bit of shrink sleeving, so just the tip is exposed; just enough to stick into the pin under test.

I've build Jim's LED/switch for my 1994 C280 with the 38 pin connector. I used male pins from an RS-232 connector. They fit the 38 pin diagnostic connector in the C280. They are available at Radio Shack, as are the other parts.

As previoulsly suggested, solder and heat shrink the pin to wire junction.

I did have a problem with reading some codes, the voltage at the pin was not +12 volts, but varied from +9 to +10 volts. Couldn't get a code read from those pins, but the rest worked OK.

I was able to read and clear the codes and solve several problems. My mechanic even came up with the same codes when he corrected the problem.

Jim and Gene,

Thanks!

The RS232 pins are an EXCELLENT IDEA! As a computer geek, I'm surprised I did not think of that earlier. Thanks again.

Jim,

Based on your website, below are 10 different "systems " that I check codes for. Each one uses a different pin on the X11/4. Is this true? Are these all available to my 94 E420 (California)? Any others that I'm missing?


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
Automatic Air Conditioner [A/C] Operational Check and Diagnostics DTCs

F1 Fuse
 

I can't seem to find 0.1 amp fuse for circuit. I am using 0.25amp. Can somebody verify that if it is ok to use .25amp fuse for the led box.

thanks

The newer design I used did not have an inline fuse.... so I did not add one. I might have if I could have found the right fuse. Also, Radio Shack sells 12volt LEDs now, so there is no need for the resistor.

I believe that's correct. . .
 

I even know the pin numbers without looking then up!!

Distributor Ignition Module [DI] DTCs = 17
Diagnostic Module [DM] DTCs = 19
Hot Wire, Sequential Fuel Injection Module [LH-SFI] DTCs = 4
Base Module [BM] DTCs = 8
Electronic Accelerator/Cruise Cntrl/Idle Speed Cntrl Module [EA/CC/ISC] DTCs = 7
Anti-lock Brake System w/ Acceleration Slip Regulation Control Module [ABS/ASR] DTCs = 6
Supplemental Restraint System [SRS] DTCs = 30
Anti-Theft Alarm System [ATA] DTCs = 23
->Convenience Features [CF] DTCs = 21 but not your car<-
Automatic Air Conditioner [A/C] Operational Check and Diagnostics DTCs = 16

Thanks Jim,

I'll have to make sure that those map the same to my car... I think it's in alldata... but you're probably right.

Oh yea.. by the way... the built in LED blinks along with the the one in the unit I built... so I really don't need the LED... I could just use a diode.

I have quite a few codes. Will have to look them up.

Pin 6 -- 13,25,26
Pin 7 -- 7, 11
Pin 8 -- 9, 10, 11, 12, 13
Pin 30 -- 4

Now I know that 30 is the SRS.. and 4 probably comes up because I recently took out the passenger air bag when I replaced my aspriator motor.

I have the convenience feature in my car.. why can't I get codes from that module?

Here's what my DTC Manual says for your DTCs.

Pin 6: ABS
13 - Brake Lamp Switch
25 - Left front vehicle speed sensors
26 - Right front vehicle speed sensors

Pin 7: EA
7 - CAN data bus signal from EA, ABS, LH-SFI control module faulty
11- Closed Throttle recognition signal to engine control module, LH-SFI. Fuel safety shut-off to engine control module, LH-SFI

Pin 8: Base Module
9 - Voltage supply for LH-SFI control module interrupted
10 - Same as above plus voltage supply for fuel-injectors interrupted
11 - Voltage supply for accessory equipment control module interrupted.
12 - Voltage supply for ABS or ABS/ASR or ASD control modules interrupted.
13 - NOT USED ???

Pin 30: SRS
4 - Right front ETR squib

Interesting codes! I quess you had no codes in the other modules since you didn't post any other module?

The SRS is a DIGITAL module so surprised you got codes from it.

Convience Features are reserved for the '140' car, so don't know what that pin is??? Are you sure it's '30'??

How's your wiring harness???

I would reset all of the codes and then see what comes back in a few days.

Jim,

Those were the only pins that returned a code.

I started putting together a worksheet of codes. First page has all of the readable pin locations and subsequent pages have codes for each pin.

I'm making my list using your site and comparing it to what alldata shows. I guess i'll check my CDs as well. There indeed are some subtle differences between your codes (which I assume are for the 140) and the 124. I'll be more than happy to send you the excel spreadsheet once I'm done.

Yes, I did get a 4 from Pin 30. And, it make sense... as I did take out my airbag recently to change the aspirator motor.

Again, my 94 E420 does indeed have the convenience feature module (I believe below the rear seat on driver side).... so why would I not be able to get codes out of it? Are codes only generated out of that module for a 140?

Also, I wonder if speed sensors codes are being generated because I replaced my wheels/tires with slightly larger ones?

BTW... harness was replaced in January , 2001

I will reset all of the codes and try again in a few days.

FUN STUFF FOLKS!!!

I just checked my 38 pin connector. Many of the pins don't have any contacts in them. Here are the 13 that do:

1,2,3,4,6,7,8,13,14,16,17,19,30

1-Ground
2-Voltage, circuit 87 or circuit 15z
3-Voltage, circuit 30
4-LH sequential multiport fuel injection, Engines 104,119
6-Anti-lock brake system, Electronic traction system, Acceleration slip regulation, Electronic stability program
7-Electronic accelerator, Cruise control/idle speed control
8-Base module, Brake assist
13-TNA-signal (gasoline), LH-SFI engines
14-On-off ratio, Engine 119 LH-SFI, Engine 120 LH-SFI (right)
16-Air conditioning, Models 124, 140, 202, 208, 210
17-Distributor ignition, Engines 104, 119, Engine 120 (right)
19-Diagnostic module (USA)
30-Airbag/ETR (SRS)

Of those (excluding 1-3 which are ground and voltages), only 2 have no matching DTC table (13 and 14). Does anyone know those are monitored?

Also interesting is that I don't have a pin in 23 which is supposed to monitor the Anti-Theft Alarm System. Any clues?

OK, According to ALLDATA (well.. a posted Mercedes Service Bulletin), looks like #14 is used for lambda reading.

When I hooked up my DIY LED reader's test plug to #14 (with black in #1 and red in #3), the LED lit up without even pushing the button. This tells me that it was an active ground. Needless to say, I did not push the button, as I was afraid of shorting something out.

Still trying to find out what #13 is used for. Anyone? Description is TNA-signal (gasoline), LH-SFI engines. I get no return signal with my DIY LED tool.

I thought that you had . . .
 

done a pin mapping of X11/4 and that's why you said your car had CF (pin 21). So I quess you hadn't.

See my page, MENU#4 re Lambda testing. I have the M0039 meter and use it measure the car's lambda. But you can accomplish this testing with any meter that has duty cycle. Others have used a Fluke meter: do a search and you'll find alot of info on it.

Jim,

Again, my vehicle has a convenience module as I have one-touch window rolldown and all window rollup on door locking (while holding key). Evidently, though, it is not readable on my car as there is no contact at pin #21. So, that issue is now closed.

As you suggested, I read your article #4 but am still unsure how lambda is read on my vehicle,

I don't believe I have an X11 in my car. I do have a duty cycle capable multimeter. Can I assume that Lambda is read using pins #13 "TNA" and #14 "On-Off Ratio" from the X11/4? If so, which probe goes to which pin?

Once I verify this, I should be able to use the info on your #4 page.

Thanks!

Check your email for a. . .
 

data 'sheet' on the X11 connector and M0039 Lambda tester. If you have an X11, it should be located near the DI module on the left fender.

Pin 2 (grnd), Pin 3 (O2 sensor) and pin 6 (12V) are the needed signals. So a Fluke w/ d/c should work ok!

Thanks Jim,

I know this is stupid, but how do you connect a multimeter to 3 pins?

I'm at work now (on a Unix Box) so I can't open the attachment at the moment.

Suppose I dont have an X11.. what then? Can I use the duty cycle multimeter to measure lambda using pins 13 and 14? Is there a 3rd pin need?

To measure Lamdba using a . . .
 

multimeter (MM), connect the MM 'minus' (blk) lead to ground and the 'plus' (red) to pin #3 (O2 sensor) for the X11 connector.

For the X11/4 connector, pin 14 to MM 'plus' and pin 1 to MM 'minus'.

The other pins are there for the Mercedes HHT or the M0039 which needs 12V and Ground to power it.

OK, I'll test it out today.

So the only question left is ... What is pins #13 "TNA" for and how is it read?

I plan to document all of this info.... although this thread will still be here.

OK,

Using multimeter with Duty cycle setting, connected black to pin 1 and red to pin 13. Air off and ignition on (engine off). Got 49.9%. THen started engine and tested at idle. Got 49.9% again.

Good! Now, let the engine . ..
 

warm up and you should see an 'oscillating' 50% duty cycle showing the 'lambda' system is active.

Looks good!

Jim,

Car was at full temp when tests were performed. I had just gotten back from work and kept the engine running while I went in to get my multimeter.... So it was well over 80degC.

Also... FYI...
Anyone out there have info on PIN 13?

Thanks

Just built LED Test Box and...
 

it works GREAT!

I tested all the modules available for my car in the 38-pin socket and didn't get DTCs (all came back with 1 flash). However when testing pin 30 (SRS module) the LED behaved weird:
Plugged Black in Pin#1, Red in pin#3 for Gnd and power respectively. Yellow in socket pin #30 (SRS) and pressed PB for 2-3 secs LED is ON and released PB. LED stayed on for about 1 sec then went OFF. No status reported... Not sure what that means? Any ideas?

The SRS system in . . .
 

your car is digital, so need a scanner to properly read the codes in that system.

Good deal on the rest of the car!

Uhh Digital...
 

makes perfect sense! Thanks Jim.

As I said earlier, I did get a code on SRS Pin #30. The code seemed to indicate that the passenger air bag had been unplugged. I had taken it our recently to replace the aspirator motor. Now, after clearing the code, I get a single light blink.

??
 

Why would you get a status reading from your SRS and I can't? Your E420 is 94 and mine is 95... would that be the reason? I believe JimF mentions in his site the LED box works for up to 94 models (Analog)...

I really don't think that there is a difference in the computers between the 94 and 95... but I'm no expert. You seem to be getting back some feedback per your earlier message (1 blink), so I don't really see where you have a problem.

Maybe wasn't clear...
 

Willy, maybe I wasn't clear when I described the LED behavior when testing SRS module (pin-30). Normal behavior for the LED to go ON as soon as you press PB for 2-3 seconds to initiate the test. Then it should go OFF when you release PB and then LED will blink with DTC status number. What I experienced is that the LED “stayed” ON after I released PB without any delays and then went OFF.

Got it.

I find that I have to hold mine for about 4 seconds before reading codes.

Who knows... maybe there was a change between model years... but I really doubt it.

I tested for codes last night after a long weekend trip and no codes have popped up. #30 works just like all of the others.

Willy

For extra help..
 

here is a picture of the X11/4 38-pin Diag Socket with active pins for my '95 E420 similar to what Willy found on his '94 E420. Also see more pictures below for related items.

Great picture!
 

Can't quite read the insert box. Do you have it in a more legible form?? Will post it on my page if ok.

Re SRS: It's a digital system in both '94 and '95 for 129s, 140s and 124s according to my sources.

Jim,

Yea, I'd like to get to the bottom of the SRS pin. I swear I got a code #4 on that pin.

I have a much clearer picture Jim but...
 

.. due to forum's file attachment limitations i had to cut down the resolution/size (~50k). I'll email you the photo file tomorrow (~110k) to post to your site with pleasure.