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Old 07-29-1999, 09:00 PM
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I have a '88 W201/190E2.3 and a '90 W124/300E, both originally sold in the mid-atlantic states (i.e., not California cars). I'd like to know if there are any diagnostic connectors (for engine management or A/C or anything else), and if so, how to properly hook up an LED pulse counter and initiate the pulsing -- that is, I have the "plans" to make the LED probe, but I don't know where to plug them in, or how to make the car give the pulses.
In advance, thank you.
Old 07-29-1999, 09:41 PM
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Location: Suwanee, GA, USA
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Both cars do have the pulse code readouts. You should buy the CD roms from the partshop to be able to look at which pins to use and what the code means. To get the code you should ground the pin for 3 seconds and no longer than 5. Then it will send back a ground signal in square wave form. Or pulses.
They are both located close to the battery under the hood.


Old 07-31-1999, 06:25 AM
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Location: southern pines NC
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For under $15 I built my own tester with a LED that you just count the flashes after pushing the button for 2 sec. and erase by pushing the button for 8 sec. after each code is read. The Mercedes Diagnostic Troubleshooting manual has all the listings for the codes.
Old 07-31-1999, 11:22 AM
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Location: Denver, CO, USA
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Would you mind sharing the parts list and circuit diagram for your LED counter. I'd certainly be interested as I'd bet others would be. Thanks.
Old 07-31-1999, 07:35 PM
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JCE JCE is offline
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I second the motion for a schematic/parts list! Thanks.
Old 08-01-1999, 08:51 AM
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Send me an e-mail and I will draw up a schematic and send it as an attachment.

Rod Rolfe
Old 08-01-1999, 09:48 AM
Paul F
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Does this diagnostic hook up apply to an 85 190E also?

Paul F
85 190E
85 Toyota 4X4
Old 08-01-1999, 11:51 AM
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Join Date: Apr 1999
Location: Toronto, ON, Canada
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Do you know if the engine needs to be started in order to get the pulse readout?

Also, can anyone tell me which pin I should ground to get the pulse output and to reset the computer? I already have the O2 sensor replaced, but the car still doesn't seem to get any power back...


[This message has been edited by E. Lee (edited 08-03-1999).]
Old 08-22-1999, 11:29 PM
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Sorry it took so long for a reply -- I've been away on vacation. My thanks to all who responded to my question, and yes, I'll dig up the schematic for the LED probe and post it later. Thanks to all.
Old 08-26-1999, 11:49 PM
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Hi, folks. I finally found the info on wiring your own fault code reader -- here it is (I hope it makes sense). BTW, the original source is from The STAR (the magazine of the MBCA), May/June '95.
Use a ''red'' wire for the 12v.power connection, through a 470-ohm resistor in line with an LED, to 3pt. juncture (i.e., to 2 more wires) :
1) to a yellow wire with a 1-amp fuse to a signal probe.
2) to a black or brown wire, through a n-o (normally open) momentary switch, to a ground connection.
Or, you can buy p/n 126-540-00-44, $40.
The article says to press sw. for 2-4 sec., and count...
Okay, that's the info. Thanks to all for your input.
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