12 Volts or Bust



Today I want to talk about 2001-2004 Harleys and their adventurous 12v Flash flavor features. Why? Because ya'll keep excitedly calling me about it. All the time. I hear the enthusiasm in your voice when you tell me the "ECM is fried" or "the fuel pump doesn't come on anymore" or, my favorite, "you broke it".  I can barely get in a question as you are so eager to tell me about your experience! It's obviously the most interesting topic ever.

If you don't have a clue about what I am talking about, that's ok. Keep reading. Chances are that you are just lucky... so far. Let's get at it!



From 2001 to sometime in 2004, Harley Delphi EFI ECMs (Engine/Electronic Control Module have an PIN 1 labeled: "12v FLASH" or "ALDL & FLASH PIN"



The way it works is simple! Apply 12v to that pin on the ECM when programing (ie flashing)! 

Where to get 12v? Bam. PIN 4 on the DATA LINK. Take that pins supply of volts straight back to ECM Pin 1. 



Easy 12v. Engineering brilliance. And that's what everyone did. What's the term... "Fool-Proof", right? 



HD ECUs had a few other oddities back then. One synergizes perfectly with this 12v "feature". Perfectly terrible. If the ECM fails in any part of its programming cycle, it locks up. No more communication with tools. No grounding of the system relay (fuel pump). No ECM functions at all. Nada. Yikes.



The first generation of Delphi ECM programming was pretty cool. Lots of NEW tech from HD. The move away from Marelli EFI to Delphi was, in my opinion, a huge win. In the transition, they forgot something. Or worse, they didn't foresee its need. The early Delphi ECMs had no programming to store/report a VIN! All these toddler motorcycles, running around with their names tattooed on their foreheads and they couldn't even tell you what it was. Super cute!

Took a year, maybe two, but HD decided that was best to re-educate the ECMs. It was time to flash/update and get them their much earned identity. With all their critical cables distributed, digital tech polished, technicians briefed, HD Corp sent out the battle-cry: it was time for ECM updates with every service



Here's the deal. That ECM PIN 1 needs 12 volts. Not 11.1v or 10.9v. Nope. 12 volts. A super-duper healthy motorcycle MIGHT manage to get 12v to the data port. You know: "healthy" like brand new. Like what the engineers at HD would have tested these ECM updates on. 

These speed machines have been courting love with the road. They've loosened up. Engines have in the sun without sunscreen. Wires and connectors had snow fights. Those old headlights suck down juice like a child home with the babysitter. By the time philanthropic PIN 4 at the DATA LINK gets to supplying PIN 1 with EVERYTHING ITS GOT, there is a really good chance its already at 11v or less.

 I have 11v.

And what happens when you try to flash with less than 12 volts on ECM PIN1?



I wasn't there. I can only tell you how I imagine it. I imagine that over the course of a few months, hundreds of new-ish motorcycles were hooked up at dealers and updated. Maybe more. Many probably worked great! But a lot surely failed.  Now, people didn't have the same understandings we do today. This was ~2003. Blackberry was the king of fancy technology across all the land. "Apple" was still just a tasty fruit to most people. EFI systems and ECMs aren't "new" in the auto-industry in this era, but it was fairly new to HD. Without a doubt in my mind, I can confidently say that it was possible that lots of locked up ECMs were labeled "BAD" and sent in for analysis... maybe. I bet someone in Milwaukee receiving felt like it was Christmas, opening all those packages! 


I.T. 101 

Keep in mind its 2003.. ish. What do you do when something electronic stops working? For everyone that thought "Call tech support", we are not friends anymore. Most people try to turn it off and on again. Or, in the case of the ECM, unplug it and plug it back in.


That's how you fix the lock up. No joke. You just unplug the ECM, to remove all power completely, and plug the ECM back in. 

Back to "Gotcha-Christmas" in Milwaukee. All these ECMs show up... and they all work fine. Every single one is perfect. They flash flawlessly with the test equipment. The ECMs were unplugged by the technicians, likely cursed at, packaged, shipped, and plugged back in; in that process, the problem disappeared. What would you do?



I know what HD did. Come late 2004, models shipped a few grams lighter, and a slightly different ECM. 





  1. 2001-2004 HD Delphi ECMs need 12v on PIN 1 of the ECM when flashing.
  2. The supply to ECM PIN 1 is gathered from DATA PORT PIN 4 and sent via DATA PORT PIN 1.
  3. DATA PORT PIN 4 is never at 12v.
  4. Unplugging voltage hogs (headlight, amps, wideband o2s) can get DATA PORT PIN 4 to 12v.
  5. If 12v is NOT received and the ECM locks up, unplug the ECM and plug it in.
  6. This was an adventure for HD. 
  7. The adventures were handed down to you. At least a few of you every week, based on our conversations.


 Thanks for reading!

 Chad @ TechnoResearch

1 comment

  • I’m a victim of this. Great humor of what I can imagine are irate customers with a simple problem.

    Joe Petersen

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