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Discussion Starter #1 (Edited)
If you get into tuning your MS43 DME you will most likely want the ability to flash your ECU on the bench. (without plugging it into the car) It's convenient, especially for Full 512kb DME flashes, which would otherwise be a two-person job.

I spent a few days learning how to build my own cable, and I thought I'd share how to do that here. A lot of credit to the forums, especially to cwarel here on E46Fanatics, who posted a video (shown below) along with resources I used for building my cable.

What you will need
  • DME harness from a scrap car with MS43 DME
  • 12V Power Supply or Car Battery (Reliable. I used a PC PSU.)
  • Soldering/Crimping Tools & Knowledge, Basic Electrical Knowledge
  • Female OBD2 Connector (I used this one. I’ve found them as cheap as $0.99)
  • Wires for Connecting Harnesses
  • [Optional] Continuity Meter / Voltmeter (For figuring out which pin is which, this will help a lot!)
How to build your bench harness (Schematic Below)
  1. Take a look at your OBD2 harness and figure out which wires correspond to Pins 4, 7 & 16. A continuity meter will help here. Pin 4 is Ground, 7 is K-line, 16 is Battery Positive.
  2. Grab the DME harness you removed from the scrap car and disassemble it. Keep Plugs 1 & 4. Remove Plugs 2, 3 & 5.
  3. Take look at Plug 4 from the DME harness. Figure out which wires go to pin 32 (K-Line) and pin 26 (Battery Power). On every e46 I’ve seen K-Line (P32) is white with purple stripes and Battery Power (P26) is green with purple stripes. This DOES NOT mean that your car will have the same colors: Double-check or risk a bricked DME.
  4. Take look at Plug 1 from the DME harness. Figure out which wires go to pins 1, 7 & 8 (Battery Power) and pins 4, 5 & 6 (Chassis Ground).
  5. Grab your soldering iron or electrical crimps, we will be making a lot of connections. Make sure your connections are good. If these come loose during a flash, you may end up with a bricked DME.
  6. Connect together all your Battery Power leads (Pin 16 from you OBD2, Pins 1, 7 & 8 from DME Plug 1, and Pin 26 from DME Plug 4, and the +12VDC Lead)
  7. [Optional] I put a switch on the line going to the positive DME pins to emulation ignition for use with JMGarage Flasher, but it is not necessary (as seen in schematic)
  8. Connect together all your Chassis ground leads (Pin 4 from you OBD2, Pins 4, 5 & 6 from DME Plug 1, and the -12VDC Lead)
  9. Connect together all your K-Line leads (Pin 7 from you OBD2, Pin 3 from DME Plug 1 and Pin 32 from DME Plug 4)
  10. Shrink wrap / tape all of your connections to prevent shorts
Now you have a cable you can use to bench flash your DME! No more fumbling around in the car!

How to use your cable
  1. Plug in your power supply or connect battery (12VDC Leads)
  2. Plug your DME into the harness you built
  3. Connect your configured K-DCAN Cable to your PC
  4. Plug your K-DCAN Cable into your bench harness
  5. If you put in a switch, turn it on to emulate switching on the ignition. Without it, the DME will behave as if the ignition is on all the time
  6. Use Galleto, JMGarage Flasher, or Chipster MSS5x Flasher as you normally would
Wiring Schematic


Additional Resources / Troubleshooting
Notes!!!
  • As always, I am not liable if you mess up your DME using this guide. Please take precaution to avoid screwing things up.
  • PLEASE, for the love of god, use a RELIABLE Power Supply with enough amperage to power the DME. (See “What you will need”) If your PSU fails during a flash you could very easily end up with a bricked DME. This is more important than even the quality of your solder/crimp joints.
  • It’s helpful to flash a DME from the Junkers for your tuning purposes. Any Siemens MS43 ECU works, part numbers don’t really matter. This way you’ll have a “known good” DME with stock firmware is you mess up.
  • If your are just tuning your DME you DO NOT have to put your ECU into boot mode. Opening up your DME increases your risk on bricking (destroying) your DME. Only open your DME any put it in boot mode when using JMGarage Flasher.
 

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Thanks for the diy. I posted it in the ms43 tuning thread a while back but that got lost with the thousands of posts. You don't need a 5A power supply, my power supply from harbor freight outputs about 1A and does the job just fine. I've probably done 30+ flashes
 

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Discussion Starter #3
Thanks, I'll go ahead and update that now, I can remember where i stumbled across that amperage rating. I thought better safe than sorry.
 

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Looking for options for a cheap portable power supply for this. Any suggestions?
 

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Looking for options for a cheap portable power supply for this. Any suggestions?
I've been using this for all of my projects but for DME flashing, you can just use a harbor freight battery charger
 
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