OK, now I'm stumped. I've read here after searching that my car should have onboard diagnostics in the form of that little box with the LED. I've been looking for it all over the area of the battery, and I'm at a loss. I'm beginning to think that mine is MIA. Attached are pics of the area; if anyone notices anything I'm missing, please let me know. I do see an 8 pins recepticle that I'm thinking might be my solution (with a scanner). Please let me know if my thinking is correct. Also, there seems to be a ground strap or something unhooked (also in the pics); I'm assuming that this should simply be grounded out, right? Thank you in advance.

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1989 300E 144K

That is early connector..you need a tool to get those codes.

Always state the model/yr on 124 b/c there are several different systems during production. I will assume you are talking of the 300e in the Sig...

http://www.geocities.com/MotorCity/Downs/1039/mercedes/cs1000_mb.pdf

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A Dalton

Yes, it is my 89. I found these schematics on another post (they might even be from you!). Is this something I can use? The scanner looks to be quite expensive, and if this will work instead, I could put the money somewhere else...

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1989 300E 144K

Yeah,,that's mine.

RadioShack..$10 at the most.

Just make sure you get the 12v led [ w/built-in resistor]..

Then go to the site I posted for you and look up the codes and plugs for your chassis..

Simple and cheap.

Post the codes when you get them..I just might know what they indicate

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A Dalton

Thank you so much!

As an update, I think you might have seen my other post a week or so back about my temp sensor. There wasn't really any change. I found that I had a blown fuse on my OVP, and replaced that. ABS light went out, idle dropped in drive (not in park, though), and cued up the Check Engine light. Finally! Now, it's very hard to start without lots of accelorator pumping, and misses pretty bad when driving. I removed that fuse, so that it was easier to start. And now, I want to do a scan so that I can fix this headache.

Please check out this post:

300E Cold start issues

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1989 300E 144K

Also, just confirm on this tool:

When testing, I hook the red (pin 16) to the + on my battery; the black (pin1) to the - on the battery, and the "any other color" to the each terminal (one at a time) on the diagnostics box, right? Then, when I press the button, it should flash my numbers? Thanks for your help; this is a completely different beast from what I'm used to (the good old, MECHANICAL om617)!

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1989 300E 144K

Those pin # are just there b/c that was a Post for the later 16 pin DM [ e320 systems]...so . disregard those and just make the tool ..the important part is the COLORS Red+/Blk-/ and odd to the requires modules pin designation [ post I gave you]

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A Dalton

Thanks! I'm going to try to get these parts tonight or tomorrow morning. I will post my findings!

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1989 300E 144K

there are only 2 things that'll trip the check engine light....the O2 sensor is one and the fuel filler cap can do it....believe me...nothing else will trip that light short of a short.....assuming coolant and oil are up to spek and the car is running at all....i'd replace the O2 sensor anyway...good luck

Yes the LED was a california spec deal as per the owners manual alot like my 400E does not have a CEL. I also agree with Cliffmac on the reason it is throwing a code, except also adjust your duty cycle after replacing the O2 sensor.

How do I adjust duty cycle, just disconnect the battery for a little while after replacing?

Also, to Arthur. I've made the tool, but when I plug in the terminals at the test box, the LED simply lights solid. I've wired it as the diagram states, assuming that the wire for the test terminal is just spliced in between the switch and the LED. Is this correct, or is the ground supposed to run THROUGH the test terminal? To elaborate: I have the + side of the LED running to battery pos, one end of the switch going to ground (- on battery, or teminal 1 on test box), and in between, 1 splice that runs to the corresponding terminal on test box. Does this sound right? Thanks,

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1989 300E 144K

The test terminal has to be from the chart I sent you to.

Test the tool:

On the bat , place the red on + and the odd on -
Led should lite

Red on + and Blk on -
Led should lite ONLY when sw is ON

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A Dalton

OK. I got it to work (I wasn't holding the button for several seconds first...). I have a code on terminal 6 (supplemental restraint, code is 8), but when I tried to get to the fuel diagnostics socket (2), it is empty. Just an empty hole, no post. 6 and 7 are the only terminals with posts in them (DOH!). I'm not seeing any wires laying around that were pushed out (or fell out, or whatever). Is there any other means of diagnosing? Or am I stuck with a halfassed diagnostics box? Thanks!

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1989 300E 144K

That chassis should have a CIS system socket at pin 3 [ not 2], unless it is Fed version.

See if there is a yellow Emmissions sticker under hood stating Cal Emmissions.

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A Dalton

The only yellow sticker I see is on the airbox, but it is faded to where you can't read it. I did check socket three (not two, please read that as a typo), but it is just an empty hole.

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1989 300E 144K